diff --git a/src/common/upload.ts b/src/common/upload.ts
index e28002ad..8c65675d 100644
--- a/src/common/upload.ts
+++ b/src/common/upload.ts
@@ -84,11 +84,13 @@ export class TurboAuthenticatedUploadService
     signal,
   }: TurboFileFactory &
     TurboAbortSignal): Promise<TurboUploadDataItemResponse> {
-    const { signedDataItem, signedDataItemSize } =
+    const { dataItemStreamFactory, dataItemSizeFactory } =
       await this.signer.signDataItem({
         fileStreamFactory,
         fileSizeFactory,
       });
+    const signedDataItem = dataItemStreamFactory();
+    const fileSize = dataItemSizeFactory();
     // TODO: add p-limit constraint or replace with separate upload class
     return this.httpService.post<TurboUploadDataItemResponse>({
       endpoint: `/tx`,
@@ -96,7 +98,7 @@ export class TurboAuthenticatedUploadService
       data: signedDataItem,
       headers: {
         'content-type': 'application/octet-stream',
-        'content-length': `${signedDataItemSize}`,
+        'content-length': `${fileSize}`,
       },
     });
   }
diff --git a/src/node/signer.ts b/src/node/signer.ts
index 3bff6ab4..8c1184a3 100644
--- a/src/node/signer.ts
+++ b/src/node/signer.ts
@@ -20,12 +20,9 @@ import { randomBytes } from 'node:crypto';
 import { Readable } from 'node:stream';
 
 import { JWKInterface } from '../common/jwk.js';
-import { TurboWalletSigner } from '../types.js';
+import { StreamSizeFactory, TurboWalletSigner } from '../types.js';
 import { toB64Url } from '../utils/base64.js';
 
-// TODO: is this deterministic for arweave wallets?
-export const SIGNED_DATA_ITEM_HEADERS_SIZE = 1044;
-
 export class TurboNodeArweaveSigner implements TurboWalletSigner {
   protected privateKey: JWKInterface;
   protected signer: ArweaveSigner; // TODO: replace with internal signer class
@@ -41,17 +38,20 @@ export class TurboNodeArweaveSigner implements TurboWalletSigner {
     fileSizeFactory,
   }: {
     fileStreamFactory: () => Readable;
-    fileSizeFactory: () => number;
+    fileSizeFactory: StreamSizeFactory;
   }): Promise<{
-    signedDataItem: Readable;
-    signedDataItemSize: number;
+    dataItemStreamFactory: () => Readable;
+    dataItemSizeFactory: StreamSizeFactory;
   }> {
     // TODO: replace with our own signer implementation
     const [stream1, stream2] = [fileStreamFactory(), fileStreamFactory()];
     const signedDataItem = await streamSigner(stream1, stream2, this.signer);
+    const signedDataItemSize = this.calculateSignedDataHeadersSize({
+      dataSize: fileSizeFactory(),
+    });
     return {
-      signedDataItem: signedDataItem,
-      signedDataItemSize: fileSizeFactory() + SIGNED_DATA_ITEM_HEADERS_SIZE,
+      dataItemStreamFactory: () => signedDataItem,
+      dataItemSizeFactory: () => signedDataItemSize,
     };
   }
 
@@ -67,4 +67,28 @@ export class TurboNodeArweaveSigner implements TurboWalletSigner {
       'x-signature': toB64Url(Buffer.from(signature)),
     };
   }
+
+  // TODO: make dynamic that accepts anchor and target and tags to return the size of the headers + data
+  // reference https://github.com/ArweaveTeam/arweave-standards/blob/master/ans/ANS-104.md#13-dataitem-format
+  private calculateSignedDataHeadersSize({ dataSize }: { dataSize: number }) {
+    const anchor = 1; // + whatever they provide (max of 33)
+    const target = 1; // + whatever they provide (max of 33)
+    const tags = 0;
+    const signatureLength = 512;
+    const ownerLength = 512;
+    const signatureTypeLength = 2;
+    const numOfTagsLength = 8; // https://github.com/Bundlr-Network/arbundles/blob/master/src/tags.ts#L191-L198
+    const numOfTagsBytesLength = 8;
+    return [
+      anchor,
+      target,
+      tags,
+      signatureLength,
+      ownerLength,
+      signatureTypeLength,
+      numOfTagsLength,
+      numOfTagsBytesLength,
+      dataSize,
+    ].reduce((totalSize, currentSize) => (totalSize += currentSize));
+  }
 }
diff --git a/src/types.ts b/src/types.ts
index 44b124fe..11692acd 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -159,10 +159,7 @@ export interface TurboWalletSigner {
   signDataItem({
     fileStreamFactory,
     fileSizeFactory,
-  }: TurboFileFactory): Promise<{
-    signedDataItem: Readable | Buffer;
-    signedDataItemSize: number;
-  }>;
+  }: TurboFileFactory): Promise<TurboSignedDataItemFactory>;
   generateSignedRequestHeaders(): Promise<TurboSignedRequestHeaders>;
 }
 
diff --git a/src/web/signer.ts b/src/web/signer.ts
index c5b98c0a..6d96774a 100644
--- a/src/web/signer.ts
+++ b/src/web/signer.ts
@@ -40,8 +40,9 @@ export class TurboWebArweaveSigner implements TurboWalletSigner {
     fileStreamFactory: () => ReadableStream;
     fileSizeFactory: StreamSizeFactory;
   }): Promise<{
-    signedDataItem: Buffer;
-    signedDataItemSize: number;
+    // axios only supports Readables, Buffers, or Blobs - so we need to convert the stream to a buffer
+    dataItemStreamFactory: () => Buffer;
+    dataItemSizeFactory: StreamSizeFactory;
   }> {
     // TODO: converts the readable stream to a buffer bc incrementally signing ReadableStreams is not trivial
     const buffer = await readableStreamToBuffer({
@@ -51,8 +52,8 @@ export class TurboWebArweaveSigner implements TurboWalletSigner {
     const signedDataItem = createData(buffer, this.signer);
     await signedDataItem.sign(this.signer);
     return {
-      signedDataItem: signedDataItem.getRaw(),
-      signedDataItemSize: signedDataItem.getRaw().length,
+      dataItemStreamFactory: () => signedDataItem.getRaw(),
+      dataItemSizeFactory: () => signedDataItem.getRaw().length,
     };
   }