diff --git a/CHANGELOG.md b/CHANGELOG.md
index 36eb4dbbea3b..5cb720fb984c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,7 +13,8 @@
 - `[jest-haste-map]` [**BREAKING**] Remove name from hash in `HasteMap.getCacheFilePath` ([#7218](https://github.com/facebook/jest/pull/7218))
 - `[babel-preset-jest]` [**BREAKING**] Export a function instead of an object for Babel 7 compatibility ([#7203](https://github.com/facebook/jest/pull/7203))
 - `[jest-haste-map]` [**BREAKING**] Expose relative paths when getting the file iterator ([#7321](https://github.com/facebook/jest/pull/7321))
-- `[jest-cli]` Print version ending in `-dev` when running a local Jest clone
+- `[jest-haste-map]` Add `hasteFS.getSize(path)` ([#7580](https://github.com/facebook/jest/pull/7580))
+- `[jest-cli]` Print version ending in `-dev` when running a local Jest clone ([#7582](https://github.com/facebook/jest/pull/7582))
 - `[jest-cli]` Add Support for `globalSetup` and `globalTeardown` in projects ([#6865](https://github.com/facebook/jest/pull/6865))
 - `[jest-runtime]` Add `extraGlobals` to config to load extra global variables into the execution vm ([#7454](https://github.com/facebook/jest/pull/7454))
 - `[jest-util]` Export `specialChars` containing Unicode characters and ANSI escapes for console output ([#7532](https://github.com/facebook/jest/pull/7532))
diff --git a/e2e/__tests__/haste_map_size.test.js b/e2e/__tests__/haste_map_size.test.js
new file mode 100644
index 000000000000..3dff41ae1035
--- /dev/null
+++ b/e2e/__tests__/haste_map_size.test.js
@@ -0,0 +1,60 @@
+/**
+ * Copyright (c) 2018-present, Facebook, Inc. All rights reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+'use strict';
+
+import os from 'os';
+import path from 'path';
+import HasteMap from 'jest-haste-map';
+import {cleanup, writeFiles} from '../Utils';
+
+const DIR = path.resolve(os.tmpdir(), 'haste_map_size');
+
+beforeEach(() => {
+  cleanup(DIR);
+  writeFiles(DIR, {
+    'file.js': '"abc"',
+  });
+});
+afterEach(() => cleanup(DIR));
+
+const options = {
+  extensions: ['js'],
+  forceNodeFilesystemAPI: true,
+  ignorePattern: / ^/,
+  maxWorkers: 2,
+  mocksPattern: '',
+  name: 'tmp',
+  platforms: [],
+  retainAllFiles: true,
+  rootDir: DIR,
+  roots: [DIR],
+  useWatchman: false,
+  watch: false,
+};
+
+test('reports the correct file size', async () => {
+  const hasteMap = new HasteMap(options);
+  const hasteFS = (await hasteMap.build()).hasteFS;
+  expect(hasteFS.getSize(path.join(DIR, 'file.js'))).toBe(5);
+});
+
+test('updates the file size when a file changes', async () => {
+  const hasteMap = new HasteMap({...options, watch: true});
+  await hasteMap.build();
+
+  writeFiles(DIR, {
+    'file.js': '"asdf"',
+  });
+  const {hasteFS} = await new Promise(resolve =>
+    hasteMap.once('change', resolve),
+  );
+  hasteMap.end();
+  expect(hasteFS.getSize(path.join(DIR, 'file.js'))).toBe(6);
+});
diff --git a/packages/jest-cli/src/TestSequencer.js b/packages/jest-cli/src/TestSequencer.js
index a48d24d2cfcb..fe51829fa58c 100644
--- a/packages/jest-cli/src/TestSequencer.js
+++ b/packages/jest-cli/src/TestSequencer.js
@@ -69,8 +69,8 @@ export default class TestSequencer {
   // fastest results.
   sort(tests: Array<Test>): Array<Test> {
     const stats = {};
-    const fileSize = test =>
-      stats[test.path] || (stats[test.path] = fs.statSync(test.path).size);
+    const fileSize = ({path, context: {hasteFS}}) =>
+      stats[path] || (stats[path] = hasteFS.getSize(path) || 0);
     const hasFailed = (cache, test) =>
       cache[test.path] && cache[test.path][0] === FAIL;
     const time = (cache, test) => cache[test.path] && cache[test.path][1];
diff --git a/packages/jest-cli/src/__tests__/test_sequencer.test.js b/packages/jest-cli/src/__tests__/test_sequencer.test.js
index fc03b111d053..95c8000c3191 100644
--- a/packages/jest-cli/src/__tests__/test_sequencer.test.js
+++ b/packages/jest-cli/src/__tests__/test_sequencer.test.js
@@ -23,6 +23,9 @@ const context = {
     cacheDirectory: '/cache',
     name: 'test',
   },
+  hasteFS: {
+    getSize: path => path.length,
+  },
 };
 
 const secondContext = {
@@ -31,6 +34,9 @@ const secondContext = {
     cacheDirectory: '/cache2',
     name: 'test2',
   },
+  hasteFS: {
+    getSize: path => path.length,
+  },
 };
 
 const toTests = paths =>
@@ -45,7 +51,6 @@ beforeEach(() => {
 
   fs.readFileSync = jest.fn(() => '{}');
   fs.existsSync = () => true;
-  fs.statSync = jest.fn(filePath => ({size: filePath.length}));
   fs.writeFileSync = jest.fn();
 });
 
diff --git a/packages/jest-haste-map/src/HasteFS.js b/packages/jest-haste-map/src/HasteFS.js
index c80432dd47e4..617ef744850e 100644
--- a/packages/jest-haste-map/src/HasteFS.js
+++ b/packages/jest-haste-map/src/HasteFS.js
@@ -28,6 +28,11 @@ export default class HasteFS {
     return (fileMetadata && fileMetadata[H.ID]) || null;
   }
 
+  getSize(file: Path): ?number {
+    const fileMetadata = this._getFileData(file);
+    return (fileMetadata && fileMetadata[H.SIZE]) || null;
+  }
+
   getDependencies(file: Path): ?Array<string> {
     const fileMetadata = this._getFileData(file);
     return (fileMetadata && fileMetadata[H.DEPENDENCIES]) || null;
diff --git a/packages/jest-haste-map/src/__tests__/index.test.js b/packages/jest-haste-map/src/__tests__/index.test.js
index d97892877cbd..50a95c8182ec 100644
--- a/packages/jest-haste-map/src/__tests__/index.test.js
+++ b/packages/jest-haste-map/src/__tests__/index.test.js
@@ -51,7 +51,7 @@ jest.mock('../crawlers/watchman', () =>
         if (list[file]) {
           const hash = computeSha1 ? mockHashContents(list[file]) : null;
 
-          data.files.set(relativeFilePath, ['', 32, 0, [], hash]);
+          data.files.set(relativeFilePath, ['', 32, 42, 0, [], hash]);
         } else {
           data.files.delete(relativeFilePath);
         }
@@ -337,14 +337,15 @@ describe('HasteMap', () => {
 
       expect(data.files).toEqual(
         createMap({
-          'fruits/Banana.js': ['Banana', 32, 1, ['Strawberry'], null],
-          'fruits/Pear.js': ['Pear', 32, 1, ['Banana', 'Strawberry'], null],
-          'fruits/Strawberry.js': ['Strawberry', 32, 1, [], null],
-          'fruits/__mocks__/Pear.js': ['', 32, 1, ['Melon'], null],
+          'fruits/Banana.js': ['Banana', 32, 42, 1, ['Strawberry'], null],
+          'fruits/Pear.js': ['Pear', 32, 42, 1, ['Banana', 'Strawberry'], null],
+          'fruits/Strawberry.js': ['Strawberry', 32, 42, 1, [], null],
+          'fruits/__mocks__/Pear.js': ['', 32, 42, 1, ['Melon'], null],
           // node modules
           'fruits/node_modules/fbjs/lib/flatMap.js': [
             'flatMap',
             32,
+            42,
             1,
             [],
             null,
@@ -352,11 +353,12 @@ describe('HasteMap', () => {
           'fruits/node_modules/react/React.js': [
             'React',
             32,
+            42,
             1,
             ['Component'],
             null,
           ],
-          'vegetables/Melon.js': ['Melon', 32, 1, [], null],
+          'vegetables/Melon.js': ['Melon', 32, 42, 1, [], null],
         }),
       );
 
@@ -405,11 +407,18 @@ describe('HasteMap', () => {
 
           // The node crawler returns "null" for the SHA-1.
           data.files = createMap({
-            'fruits/Banana.js': ['Banana', 32, 0, ['Strawberry'], null],
-            'fruits/Pear.js': ['Pear', 32, 0, ['Banana', 'Strawberry'], null],
-            'fruits/Strawberry.js': ['Strawberry', 32, 0, [], null],
-            'fruits/__mocks__/Pear.js': ['', 32, 0, ['Melon'], null],
-            'vegetables/Melon.js': ['Melon', 32, 0, [], null],
+            'fruits/Banana.js': ['Banana', 32, 42, 0, ['Strawberry'], null],
+            'fruits/Pear.js': [
+              'Pear',
+              32,
+              42,
+              0,
+              ['Banana', 'Strawberry'],
+              null,
+            ],
+            'fruits/Strawberry.js': ['Strawberry', 32, 42, 0, [], null],
+            'fruits/__mocks__/Pear.js': ['', 32, 42, 0, ['Melon'], null],
+            'vegetables/Melon.js': ['Melon', 32, 42, 0, [], null],
           });
 
           return Promise.resolve(data);
@@ -430,6 +439,7 @@ describe('HasteMap', () => {
             'fruits/Banana.js': [
               'Banana',
               32,
+              42,
               1,
               ['Strawberry'],
               '7772b628e422e8cf59c526be4bb9f44c0898e3d1',
@@ -437,6 +447,7 @@ describe('HasteMap', () => {
             'fruits/Pear.js': [
               'Pear',
               32,
+              42,
               1,
               ['Banana', 'Strawberry'],
               '89d0c2cc11dcc5e1df50b8af04ab1b597acfba2f',
@@ -444,6 +455,7 @@ describe('HasteMap', () => {
             'fruits/Strawberry.js': [
               'Strawberry',
               32,
+              42,
               1,
               [],
               'e8aa38e232b3795f062f1d777731d9240c0f8c25',
@@ -451,6 +463,7 @@ describe('HasteMap', () => {
             'fruits/__mocks__/Pear.js': [
               '',
               32,
+              42,
               1,
               ['Melon'],
               '8d40afbb6e2dc78e1ba383b6d02cafad35cceef2',
@@ -458,6 +471,7 @@ describe('HasteMap', () => {
             'vegetables/Melon.js': [
               'Melon',
               32,
+              42,
               1,
               [],
               'f16ccf6f2334ceff2ddb47628a2c5f2d748198ca',
@@ -507,6 +521,7 @@ describe('HasteMap', () => {
       expect(data.files.get('fruits/node_modules/fbjs/fbjs.js')).toEqual([
         '',
         32,
+        42,
         0,
         [],
         null,
@@ -604,6 +619,7 @@ describe('HasteMap', () => {
             'fruits/Strawberry.android.js': [
               'Strawberry',
               32,
+              42,
               1,
               ['Blackberry'],
               null,
@@ -611,11 +627,12 @@ describe('HasteMap', () => {
             'fruits/Strawberry.ios.js': [
               'Strawberry',
               32,
+              42,
               1,
               ['Raspberry'],
               null,
             ],
-            'fruits/Strawberry.js': ['Strawberry', 32, 1, ['Banana'], null],
+            'fruits/Strawberry.js': ['Strawberry', 32, 42, 1, ['Banana'], null],
           }),
         );
 
@@ -702,7 +719,14 @@ describe('HasteMap', () => {
             expect(useBuitinsInContext(data.clocks)).toEqual(mockClocks);
 
             const files = new Map(initialData.files);
-            files.set('fruits/Banana.js', ['Banana', 32, 1, ['Kiwi'], null]);
+            files.set('fruits/Banana.js', [
+              'Banana',
+              32,
+              42,
+              1,
+              ['Kiwi'],
+              null,
+            ]);
 
             expect(useBuitinsInContext(data.files)).toEqual(files);
 
@@ -962,7 +986,7 @@ describe('HasteMap', () => {
     watchman.mockImplementation(options =>
       mockImpl(options).then(() => {
         const {data} = options;
-        data.files.set('fruits/invalid/file.js', ['', 34, 0, []]);
+        data.files.set('fruits/invalid/file.js', ['', 34, 44, 0, []]);
         return data;
       }),
     );
@@ -1060,7 +1084,7 @@ describe('HasteMap', () => {
     node.mockImplementation(options => {
       const {data} = options;
       data.files = createMap({
-        'fruits/Banana.js': ['', 32, 0, [], null],
+        'fruits/Banana.js': ['', 32, 42, 0, [], null],
       });
       return Promise.resolve(data);
     });
@@ -1073,7 +1097,7 @@ describe('HasteMap', () => {
 
         expect(data.files).toEqual(
           createMap({
-            'fruits/Banana.js': ['Banana', 32, 1, ['Strawberry'], null],
+            'fruits/Banana.js': ['Banana', 32, 42, 1, ['Strawberry'], null],
           }),
         );
 
@@ -1091,7 +1115,7 @@ describe('HasteMap', () => {
     node.mockImplementation(options => {
       const {data} = options;
       data.files = createMap({
-        'fruits/Banana.js': ['', 32, 0, [], null],
+        'fruits/Banana.js': ['', 32, 42, 0, [], null],
       });
       return Promise.resolve(data);
     });
@@ -1104,7 +1128,7 @@ describe('HasteMap', () => {
 
         expect(data.files).toEqual(
           createMap({
-            'fruits/Banana.js': ['Banana', 32, 1, ['Strawberry'], null],
+            'fruits/Banana.js': ['Banana', 32, 42, 1, ['Strawberry'], null],
           }),
         );
       });
@@ -1184,11 +1208,13 @@ describe('HasteMap', () => {
     const MOCK_STAT_FILE = {
       isDirectory: () => false,
       mtime: {getTime: () => 45},
+      size: 55,
     };
 
     const MOCK_STAT_FOLDER = {
       isDirectory: () => true,
       mtime: {getTime: () => 45},
+      size: 55,
     };
 
     hm_it('handles several change events at once', async hm => {
diff --git a/packages/jest-haste-map/src/constants.js b/packages/jest-haste-map/src/constants.js
index 11ab681ab814..6bbe7c4fb52e 100644
--- a/packages/jest-haste-map/src/constants.js
+++ b/packages/jest-haste-map/src/constants.js
@@ -20,9 +20,10 @@ export default {
   /* file map attributes */
   ID: 0,
   MTIME: 1,
-  VISITED: 2,
-  DEPENDENCIES: 3,
-  SHA1: 4,
+  SIZE: 2,
+  VISITED: 3,
+  DEPENDENCIES: 4,
+  SHA1: 5,
 
   /* module map attributes */
   PATH: 0,
diff --git a/packages/jest-haste-map/src/crawlers/__tests__/node.test.js b/packages/jest-haste-map/src/crawlers/__tests__/node.test.js
index a1e95e66b210..e38f5a003c2f 100644
--- a/packages/jest-haste-map/src/crawlers/__tests__/node.test.js
+++ b/packages/jest-haste-map/src/crawlers/__tests__/node.test.js
@@ -33,6 +33,7 @@ jest.mock('child_process', () => ({
 
 jest.mock('fs', () => {
   let mtime = 32;
+  const size = 42;
   const stat = (path, callback) => {
     setTimeout(
       () =>
@@ -48,6 +49,7 @@ jest.mock('fs', () => {
               return mtime++;
             },
           },
+          size,
         }),
       0,
     );
@@ -131,9 +133,9 @@ describe('node crawler', () => {
 
       expect(data.files).toEqual(
         createMap({
-          'fruits/strawberry.js': ['', 32, 0, [], null],
-          'fruits/tomato.js': ['', 33, 0, [], null],
-          'vegetables/melon.json': ['', 34, 0, [], null],
+          'fruits/strawberry.js': ['', 32, 42, 0, [], null],
+          'fruits/tomato.js': ['', 33, 42, 0, [], null],
+          'vegetables/melon.json': ['', 34, 42, 0, [], null],
         }),
       );
     });
@@ -147,9 +149,9 @@ describe('node crawler', () => {
     nodeCrawl = require('../node').default;
 
     // In this test sample, strawberry is changed and tomato is unchanged
-    const tomato = ['', 33, 1, [], null];
+    const tomato = ['', 33, 42, 1, [], null];
     const files = createMap({
-      'fruits/strawberry.js': ['', 30, 1, [], null],
+      'fruits/strawberry.js': ['', 30, 40, 1, [], null],
       'fruits/tomato.js': tomato,
     });
 
@@ -162,7 +164,7 @@ describe('node crawler', () => {
     }).then(data => {
       expect(data.files).toEqual(
         createMap({
-          'fruits/strawberry.js': ['', 32, 0, [], null],
+          'fruits/strawberry.js': ['', 32, 42, 0, [], null],
           'fruits/tomato.js': tomato,
         }),
       );
@@ -188,8 +190,8 @@ describe('node crawler', () => {
     }).then(data => {
       expect(data.files).toEqual(
         createMap({
-          'fruits/directory/strawberry.js': ['', 33, 0, [], null],
-          'fruits/tomato.js': ['', 32, 0, [], null],
+          'fruits/directory/strawberry.js': ['', 33, 42, 0, [], null],
+          'fruits/tomato.js': ['', 32, 42, 0, [], null],
         }),
       );
     });
@@ -211,8 +213,8 @@ describe('node crawler', () => {
     }).then(data => {
       expect(data.files).toEqual(
         createMap({
-          'fruits/directory/strawberry.js': ['', 33, 0, [], null],
-          'fruits/tomato.js': ['', 32, 0, [], null],
+          'fruits/directory/strawberry.js': ['', 33, 42, 0, [], null],
+          'fruits/tomato.js': ['', 32, 42, 0, [], null],
         }),
       );
     });
diff --git a/packages/jest-haste-map/src/crawlers/__tests__/watchman.test.js b/packages/jest-haste-map/src/crawlers/__tests__/watchman.test.js
index b28a4e3c869f..66816173a4da 100644
--- a/packages/jest-haste-map/src/crawlers/__tests__/watchman.test.js
+++ b/packages/jest-haste-map/src/crawlers/__tests__/watchman.test.js
@@ -79,21 +79,25 @@ describe('watchman watch', () => {
               exists: true,
               mtime_ms: {toNumber: () => 30},
               name: 'fruits/strawberry.js',
+              size: 40,
             },
             {
               exists: true,
               mtime_ms: {toNumber: () => 31},
               name: 'fruits/tomato.js',
+              size: 41,
             },
             {
               exists: true,
               mtime_ms: {toNumber: () => 32},
               name: 'fruits/pear.js',
+              size: 42,
             },
             {
               exists: true,
               mtime_ms: {toNumber: () => 33},
               name: 'vegetables/melon.json',
+              size: 43,
             },
           ],
           is_fresh_instance: true,
@@ -104,9 +108,9 @@ describe('watchman watch', () => {
     };
 
     mockFiles = createMap({
-      [MELON_RELATIVE]: ['', 33, 0, [], null],
-      [STRAWBERRY_RELATIVE]: ['', 30, 0, [], null],
-      [TOMATO_RELATIVE]: ['', 31, 0, [], null],
+      [MELON_RELATIVE]: ['', 33, 43, 0, [], null],
+      [STRAWBERRY_RELATIVE]: ['', 30, 40, 0, [], null],
+      [TOMATO_RELATIVE]: ['', 31, 41, 0, [], null],
     });
   });
 
@@ -146,7 +150,7 @@ describe('watchman watch', () => {
         ['anyof', ['dirname', 'fruits'], ['dirname', 'vegetables']],
       ]);
 
-      expect(query[2].fields).toEqual(['name', 'exists', 'mtime_ms']);
+      expect(query[2].fields).toEqual(['name', 'exists', 'mtime_ms', 'size']);
 
       expect(query[2].glob).toEqual([
         'fruits/**/*.js',
@@ -181,6 +185,7 @@ describe('watchman watch', () => {
               exists: true,
               mtime_ms: {toNumber: () => 33},
               name: 'vegetables/durian.zip',
+              size: 43,
             },
           ],
           is_fresh_instance: true,
@@ -206,8 +211,8 @@ describe('watchman watch', () => {
     }).then(data => {
       expect(data.files).toEqual(
         createMap({
-          [path.join(DURIAN_RELATIVE, 'foo.1.js')]: ['', 33, 0, [], null],
-          [path.join(DURIAN_RELATIVE, 'foo.2.js')]: ['', 33, 0, [], null],
+          [path.join(DURIAN_RELATIVE, 'foo.1.js')]: ['', 33, 43, 0, [], null],
+          [path.join(DURIAN_RELATIVE, 'foo.2.js')]: ['', 33, 43, 0, [], null],
         }),
       );
     });
@@ -228,11 +233,13 @@ describe('watchman watch', () => {
               exists: true,
               mtime_ms: {toNumber: () => 42},
               name: 'fruits/kiwi.js',
+              size: 40,
             },
             {
               exists: false,
               mtime_ms: null,
               name: 'fruits/tomato.js',
+              size: 0,
             },
           ],
           is_fresh_instance: false,
@@ -267,9 +274,9 @@ describe('watchman watch', () => {
 
       expect(data.files).toEqual(
         createMap({
-          [KIWI_RELATIVE]: ['', 42, 0, [], null],
-          [MELON_RELATIVE]: ['', 33, 0, [], null],
-          [STRAWBERRY_RELATIVE]: ['', 30, 0, [], null],
+          [KIWI_RELATIVE]: ['', 42, 40, 0, [], null],
+          [MELON_RELATIVE]: ['', 33, 43, 0, [], null],
+          [STRAWBERRY_RELATIVE]: ['', 30, 40, 0, [], null],
         }),
       );
     });
@@ -292,17 +299,20 @@ describe('watchman watch', () => {
               exists: true,
               mtime_ms: {toNumber: () => 42},
               name: 'fruits/kiwi.js',
+              size: 52,
             },
             {
               exists: true,
               mtime_ms: {toNumber: () => 41},
               name: 'fruits/banana.js',
+              size: 51,
             },
             {
               'content.sha1hex': mockTomatoSha1,
               exists: true,
               mtime_ms: {toNumber: () => 76},
               name: 'fruits/tomato.js',
+              size: 41,
             },
           ],
           is_fresh_instance: true,
@@ -312,9 +322,9 @@ describe('watchman watch', () => {
       'watch-project': WATCH_PROJECT_MOCK,
     };
 
-    const mockBananaMetadata = ['Banana', 41, 1, ['Raspberry'], null];
+    const mockBananaMetadata = ['Banana', 41, 51, 1, ['Raspberry'], null];
     mockFiles.set(BANANA_RELATIVE, mockBananaMetadata);
-    const mockTomatoMetadata = ['Tomato', 31, 1, [], mockTomatoSha1];
+    const mockTomatoMetadata = ['Tomato', 31, 41, 1, [], mockTomatoSha1];
     mockFiles.set(TOMATO_RELATIVE, mockTomatoMetadata);
 
     const clocks = createMap({
@@ -344,8 +354,8 @@ describe('watchman watch', () => {
       expect(data.files).toEqual(
         createMap({
           [BANANA_RELATIVE]: mockBananaMetadata,
-          [KIWI_RELATIVE]: ['', 42, 0, [], null],
-          [TOMATO_RELATIVE]: ['Tomato', 76, 1, [], mockTomatoSha1],
+          [KIWI_RELATIVE]: ['', 42, 52, 0, [], null],
+          [TOMATO_RELATIVE]: ['Tomato', 76, 41, 1, [], mockTomatoSha1],
         }),
       );
 
@@ -373,6 +383,7 @@ describe('watchman watch', () => {
               exists: true,
               mtime_ms: {toNumber: () => 42},
               name: 'kiwi.js',
+              size: 52,
             },
           ],
           is_fresh_instance: false,
@@ -385,6 +396,7 @@ describe('watchman watch', () => {
               exists: true,
               mtime_ms: {toNumber: () => 33},
               name: 'melon.json',
+              size: 43,
             },
           ],
           is_fresh_instance: true,
@@ -425,8 +437,8 @@ describe('watchman watch', () => {
 
       expect(data.files).toEqual(
         createMap({
-          [KIWI_RELATIVE]: ['', 42, 0, [], null],
-          [MELON_RELATIVE]: ['', 33, 0, [], null],
+          [KIWI_RELATIVE]: ['', 42, 52, 0, [], null],
+          [MELON_RELATIVE]: ['', 33, 43, 0, [], null],
         }),
       );
     });
@@ -493,7 +505,7 @@ describe('watchman watch', () => {
         ['anyof', ['suffix', 'js'], ['suffix', 'json']],
       ]);
 
-      expect(query[2].fields).toEqual(['name', 'exists', 'mtime_ms']);
+      expect(query[2].fields).toEqual(['name', 'exists', 'mtime_ms', 'size']);
 
       expect(query[2].glob).toEqual(['**/*.js', '**/*.json']);
 
diff --git a/packages/jest-haste-map/src/crawlers/node.js b/packages/jest-haste-map/src/crawlers/node.js
index e61a06f714e1..d182556dcb12 100644
--- a/packages/jest-haste-map/src/crawlers/node.js
+++ b/packages/jest-haste-map/src/crawlers/node.js
@@ -16,7 +16,9 @@ import {spawn} from 'child_process';
 import H from '../constants';
 import * as fastPath from '../lib/fast_path';
 
-type Callback = (result: Array<[/* id */ string, /* mtime */ number]>) => void;
+type Callback = (
+  result: Array<[/* id */ string, /* mtime */ number, /* size */ number]>,
+) => void;
 
 function find(
   roots: Array<string>,
@@ -51,7 +53,7 @@ function find(
             } else {
               const ext = path.extname(file).substr(1);
               if (extensions.indexOf(ext) !== -1) {
-                result.push([file, stat.mtime.getTime()]);
+                result.push([file, stat.mtime.getTime(), stat.size]);
               }
             }
           }
@@ -114,7 +116,7 @@ function findNative(
       lines.forEach(path => {
         fs.stat(path, (err, stat) => {
           if (!err && stat) {
-            result.push([path, stat.mtime.getTime()]);
+            result.push([path, stat.mtime.getTime(), stat.size]);
           }
           if (--count === 0) {
             callback(result);
@@ -148,12 +150,13 @@ export default function nodeCrawl(
         const filePath = fileData[0];
         const relativeFilePath = fastPath.relative(rootDir, filePath);
         const mtime = fileData[1];
+        const size = fileData[2];
         const existingFile = data.files.get(relativeFilePath);
         if (existingFile && existingFile[H.MTIME] === mtime) {
           files.set(relativeFilePath, existingFile);
         } else {
           // See ../constants.js; SHA-1 will always be null and fulfilled later.
-          files.set(relativeFilePath, ['', mtime, 0, [], null]);
+          files.set(relativeFilePath, ['', mtime, size, 0, [], null]);
         }
       });
       data.files = files;
diff --git a/packages/jest-haste-map/src/crawlers/watchman.js b/packages/jest-haste-map/src/crawlers/watchman.js
index f6b1f5830184..4728c120c320 100644
--- a/packages/jest-haste-map/src/crawlers/watchman.js
+++ b/packages/jest-haste-map/src/crawlers/watchman.js
@@ -29,7 +29,7 @@ function WatchmanError(error: Error): Error {
 export default async function watchmanCrawl(
   options: CrawlerOptions,
 ): Promise<InternalHasteMap> {
-  const fields = ['name', 'exists', 'mtime_ms'];
+  const fields = ['name', 'exists', 'mtime_ms', 'size'];
   const {data, extensions, ignore, rootDir, roots} = options;
   const defaultWatchExpression = [
     'allof',
@@ -173,6 +173,7 @@ export default async function watchmanCrawl(
           typeof fileData.mtime_ms === 'number'
             ? fileData.mtime_ms
             : fileData.mtime_ms.toNumber();
+        const size = fileData.size;
 
         let sha1hex = fileData['content.sha1hex'];
         if (typeof sha1hex !== 'string' || sha1hex.length !== 40) {
@@ -193,7 +194,7 @@ export default async function watchmanCrawl(
           nextData[1] = mtime;
         } else {
           // See ../constants.js
-          nextData = ['', mtime, 0, [], sha1hex];
+          nextData = ['', mtime, size, 0, [], sha1hex];
         }
 
         const mappings = options.mapper ? options.mapper(filePath) : null;
diff --git a/packages/jest-haste-map/src/index.js b/packages/jest-haste-map/src/index.js
index f2b8021a2907..65cfe50d92d2 100644
--- a/packages/jest-haste-map/src/index.js
+++ b/packages/jest-haste-map/src/index.js
@@ -170,6 +170,7 @@ const getWhiteList = (list: ?Array<string>): ?RegExp => {
  * type FileMetaData = {
  *   id: ?string, // used to look up module metadata objects in `map`.
  *   mtime: number, // check for outdated files.
+ *   size: number, // size of the file in bytes.
  *   visited: boolean, // whether the file has been parsed or not.
  *   dependencies: Array<string>, // all relative dependencies of this file.
  *   sha1: ?string, // SHA-1 of the file, if requested via options.
@@ -188,8 +189,8 @@ const getWhiteList = (list: ?Array<string>): ?RegExp => {
  *
  * Note that the data structures described above are conceptual only. The actual
  * implementation uses arrays and constant keys for metadata storage. Instead of
- * `{id: 'flatMap', mtime: 3421, visited: true, dependencies: []}` the real
- * representation is similar to `['flatMap', 3421, 1, []]` to save storage space
+ * `{id: 'flatMap', mtime: 3421, size: 42, visited: true, dependencies: []}` the real
+ * representation is similar to `['flatMap', 3421, 42, 1, []]` to save storage space
  * and reduce parse and write time of a big JSON blob.
  *
  * The HasteMap is created as follows:
@@ -892,7 +893,14 @@ class HasteMap extends EventEmitter {
               stat,
               'since the file exists or changed, it should have stats',
             );
-            const fileMetadata = ['', stat.mtime.getTime(), 0, [], null];
+            const fileMetadata = [
+              '',
+              stat.mtime.getTime(),
+              stat.size,
+              0,
+              [],
+              null,
+            ];
             hasteMap.files.set(relativeFilePath, fileMetadata);
             const promise = this._processFile(
               hasteMap,
diff --git a/types/HasteMap.js b/types/HasteMap.js
index 88815cd8ef2e..6c3d59d8afd9 100644
--- a/types/HasteMap.js
+++ b/types/HasteMap.js
@@ -51,6 +51,7 @@ export type RawModuleMap = {|
 export type FileMetaData = [
   /* id */ string,
   /* mtime */ number,
+  /* size */ number,
   /* visited */ 0 | 1,
   /* dependencies */ Array<string>,
   /* sha1 */ ?string,
@@ -62,8 +63,9 @@ export type ModuleMetaData = [Path, /* type */ number];
 export type HType = {|
   ID: 0,
   MTIME: 1,
-  VISITED: 2,
-  DEPENDENCIES: 3,
+  SIZE: 2,
+  VISITED: 3,
+  DEPENDENCIES: 4,
   PATH: 0,
   TYPE: 1,
   MODULE: 0,
@@ -72,4 +74,4 @@ export type HType = {|
   NATIVE_PLATFORM: 'native',
 |};
 
-export type HTypeValue = 0 | 1 | 2 | 3 | 'g';
+export type HTypeValue = $Values<HType>;