diff --git a/NEWS.md b/NEWS.md
index 786eb324232c8..ebfedd111f7de 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -24,6 +24,8 @@ New library functions
 Standard library changes
 ------------------------
 
+* `diagm` and `spdiagm` now accept optional `m,n` initial arguments to specify a size ([#31654]).
+
 #### LinearAlgebra
 
 
diff --git a/stdlib/LinearAlgebra/src/dense.jl b/stdlib/LinearAlgebra/src/dense.jl
index 349ec1457a3e6..949b1a9f06101 100644
--- a/stdlib/LinearAlgebra/src/dense.jl
+++ b/stdlib/LinearAlgebra/src/dense.jl
@@ -246,12 +246,14 @@ julia> diag(A,1)
 diag(A::AbstractMatrix, k::Integer=0) = A[diagind(A,k)]
 
 """
-    diagm(kv::Pair{<:Integer,<:AbstractVector}...; size=nothing)
+    diagm(kv::Pair{<:Integer,<:AbstractVector}...)
+    diagm(m::Integer, n::Integer, kv::Pair{<:Integer,<:AbstractVector}...)
 
 Construct a matrix from `Pair`s of diagonals and vectors.
 Vector `kv.second` will be placed on the `kv.first` diagonal.
-By default (if `size=nothing`), the matrix is square and its size is inferred
-from `kv`, but a non-square size `m`×`n` can be passed as a tuple via `size=(m,n)`.
+By default the matrix is square and its size is inferred
+from `kv`, but a non-square size `m`×`n` (padded with zeros as needed)
+can be specified by passing `m,n` as the first arguments.
 
 `diagm` constructs a full matrix; if you want storage-efficient
 versions with fast arithmetic, see [`Diagonal`](@ref), [`Bidiagonal`](@ref)
@@ -274,8 +276,10 @@ julia> diagm(1 => [1,2,3], -1 => [4,5])
  0  0  0  0
 ```
 """
-function diagm(kv::Pair{<:Integer,<:AbstractVector}...; size::Union{Nothing,Tuple{<:Integer,<:Integer}}=nothing)
-    A = diagm_container(kv...; size=size)
+diagm(kv::Pair{<:Integer,<:AbstractVector}...) = _diagm(nothing, kv...)
+diagm(m::Integer, n::Integer, kv::Pair{<:Integer,<:AbstractVector}...) = _diagm((Int(m),Int(n)), kv...)
+function _diagm(size, kv::Pair{<:Integer,<:AbstractVector}...)
+    A = diagm_container(size, kv...)
     for p in kv
         inds = diagind(A, p.first)
         for (i, val) in enumerate(p.second)
@@ -284,31 +288,32 @@ function diagm(kv::Pair{<:Integer,<:AbstractVector}...; size::Union{Nothing,Tupl
     end
     return A
 end
-function diagm_size(size::Union{Nothing,Tuple{<:Integer,<:Integer}}, kv::Pair{<:Integer,<:AbstractVector}...)
-    if isnothing(size)
-        mnmax = mapreduce(x -> length(x.second) + abs(Int(x.first)), max, kv; init=0)
-        return mnmax, mnmax
-    else
-        mmax = mapreduce(x -> length(x.second) - min(0,Int(x.first)), max, kv; init=0)
-        nmax = mapreduce(x -> length(x.second) + max(0,Int(x.first)), max, kv; init=0)
-        m, n = size
-        (m ≥ mmax && n ≥ nmax) || throw(DimensionMismatch("invalid size=$size"))
-        return m, n
-    end
+function diagm_size(size::Nothing, kv::Pair{<:Integer,<:AbstractVector}...)
+    mnmax = mapreduce(x -> length(x.second) + abs(Int(x.first)), max, kv; init=0)
+    return mnmax, mnmax
+end
+function diagm_size(size::Tuple{Int,Int}, kv::Pair{<:Integer,<:AbstractVector}...)
+    mmax = mapreduce(x -> length(x.second) - min(0,Int(x.first)), max, kv; init=0)
+    nmax = mapreduce(x -> length(x.second) + max(0,Int(x.first)), max, kv; init=0)
+    m, n = size
+    (m ≥ mmax && n ≥ nmax) || throw(DimensionMismatch("invalid size=$size"))
+    return m, n
 end
-function diagm_container(kv::Pair{<:Integer,<:AbstractVector}...; size::Union{Nothing,Tuple{<:Integer,<:Integer}}=nothing)
+function diagm_container(size, kv::Pair{<:Integer,<:AbstractVector}...)
     T = promote_type(map(x -> eltype(x.second), kv)...)
     return zeros(T, diagm_size(size, kv...)...)
 end
-diagm_container(kv::Pair{<:Integer,<:BitVector}...; size::Union{Nothing,Tuple{<:Integer,<:Integer}}=nothing) =
+diagm_container(size, kv::Pair{<:Integer,<:BitVector}...) =
     return falses(diagm_size(size, kv...)...)
 
 """
-    diagm(v::AbstractVector; size=nothing)
+    diagm(v::AbstractVector)
+    diagm(m::Integer, n::Integer, v::AbstractVector)
 
 Construct a matrix with elements of the vector as diagonal elements.
 By default (if `size=nothing`), the matrix is square and its size is given by
-`length(v)`, but a non-square size `m`×`n` can be passed as a tuple via `size=(m,n)`.
+`length(v)`, but a non-square size `m`×`n` can be specified
+by passing `m,n` as the first arguments.
 
 # Examples
 ```jldoctest
@@ -319,7 +324,8 @@ julia> diagm([1,2,3])
  0  0  3
 ```
 """
-diagm(v::AbstractVector; size::Union{Nothing,Tuple{<:Integer,<:Integer}}=nothing) = diagm(0 => v; size=size)
+diagm(v::AbstractVector) = diagm(0 => v)
+diagm(m::Integer, n::Integer, v::AbstractVector) = diagm(m, n, 0 => v)
 
 function tr(A::Matrix{T}) where T
     n = checksquare(A)
diff --git a/stdlib/LinearAlgebra/test/dense.jl b/stdlib/LinearAlgebra/test/dense.jl
index b459356a90f89..6747adf2f55aa 100644
--- a/stdlib/LinearAlgebra/test/dense.jl
+++ b/stdlib/LinearAlgebra/test/dense.jl
@@ -95,13 +95,13 @@ end
     x = [7, 8]
     for m=1:4, n=2:4
         if m < 2 || n < 3
-            @test_throws DimensionMismatch diagm(0 => x,  1 => x, size=(m,n))
-            @test_throws DimensionMismatch diagm(0 => x,  -1 => x, size=(n,m))
+            @test_throws DimensionMismatch diagm(m,n, 0 => x,  1 => x)
+            @test_throws DimensionMismatch diagm(m,n, 0 => x,  -1 => x)
         else
             M = zeros(m,n)
             M[1:2,1:3] = [7 7 0; 0 8 8]
-            @test diagm(0 => x,  1 => x, size=(m,n)) == M
-            @test diagm(0 => x,  -1 => x, size=(n,m)) == M'
+            @test diagm(m,n, 0 => x,  1 => x) == M
+            @test diagm(m,n, 0 => x,  -1 => x) == M'
         end
     end
 end
diff --git a/stdlib/SparseArrays/src/sparsematrix.jl b/stdlib/SparseArrays/src/sparsematrix.jl
index 0bdec26f6b633..0695c134a5c65 100644
--- a/stdlib/SparseArrays/src/sparsematrix.jl
+++ b/stdlib/SparseArrays/src/sparsematrix.jl
@@ -3356,12 +3356,14 @@ function spdiagm_internal(kv::Pair{<:Integer,<:AbstractVector}...)
 end
 
 """
-    spdiagm(kv::Pair{<:Integer,<:AbstractVector}...; size=nothing)
+    spdiagm(kv::Pair{<:Integer,<:AbstractVector}...)
+    spdiagm(m::Integer, n::Ingeger, kv::Pair{<:Integer,<:AbstractVector}...)
 
 Construct a sparse diagonal matrix from `Pair`s of vectors and diagonals.
 Each vector `kv.second` will be placed on the `kv.first` diagonal.  By
 default (if `size=nothing`), the matrix is square and its size is inferred
-from `kv`, but a non-square size `m`×`n` can be passed as a tuple via `size=(m,n)`.
+from `kv`, but a non-square size `m`×`n` (padded with zeros as needed)
+can be specified by passing `m,n` as the first arguments.
 
 # Examples
 ```jldoctest
@@ -3377,7 +3379,9 @@ julia> spdiagm(-1 => [1,2,3,4], 1 => [4,3,2,1])
   [4, 5]  =  1
 ```
 """
-function spdiagm(kv::Pair{<:Integer,<:AbstractVector}...; size::Union{Nothing,Tuple{<:Integer,<:Integer}}=nothing)
+_spdiagm(kv::Pair{<:Integer,<:AbstractVector}...) = _spdiagm(nothing, kv...)
+_spdiagm(m::Integer, n::Integer, kv::Pair{<:Integer,<:AbstractVector}...) = _spdiagm((Int(m),Int(n)), kv...)
+function _spdiagm(size, kv::Pair{<:Integer,<:AbstractVector}...)
     I, J, V = spdiagm_internal(kv...)
     mmax, nmax = dimlub(I), dimlub(J)
     mnmax = max(mmax, nmax)
diff --git a/stdlib/SparseArrays/test/sparse.jl b/stdlib/SparseArrays/test/sparse.jl
index 75be4ba3ddf01..3a8ee5a635bcf 100644
--- a/stdlib/SparseArrays/test/sparse.jl
+++ b/stdlib/SparseArrays/test/sparse.jl
@@ -1587,11 +1587,11 @@ end
     # non-square:
     for m=1:4, n=2:4
         if m < 2 || n < 3
-            @test_throws DimensionMismatch spdiagm(0 => x,  1 => x, size=(m,n))
+            @test_throws DimensionMismatch spdiagm(m,n, 0 => x,  1 => x)
         else
             M = zeros(m,n)
             M[1:2,1:3] = [1 1 0; 0 1 1]
-            @test spdiagm(0 => x,  1 => x, size=(m,n)) == M
+            @test spdiagm(m,n, 0 => x,  1 => x) == M
         end
     end
 end