How to Find Size of Matrix in MATLAB: Syntax and Examples

In MATLAB, use the size function to find the dimensions of a matrix. Calling size(A) returns the number of rows and columns of matrix A as a two-element vector.

Syntax

The basic syntax to find the size of a matrix A is:

• sz = size(A): Returns a vector sz where sz(1) is the number of rows and sz(2) is the number of columns.
• [m, n] = size(A): Returns the number of rows m and columns n separately.

matlab

sz = size(A);
[m, n] = size(A);

Example

This example shows how to find the size of a 3x4 matrix and get the number of rows and columns separately.

matlab

A = [1 2 3 4; 5 6 7 8; 9 10 11 12];
sz = size(A);
[m, n] = size(A);

Output

sz =
     3     4

m =
     3

n =
     4

Common Pitfalls

One common mistake is to assume size(A) returns separate values instead of a vector. Another is mixing up rows and columns when indexing the output.

Wrong way:

rows = size(A)
cols = size(A)

This assigns the full size vector to both variables.

Right way:

[rows, cols] = size(A)

matlab

A = [1 2; 3 4];
rows = size(A); % rows is [2 2], not number of rows
cols = size(A); % cols is also [2 2]

[rows, cols] = size(A); % Correct: rows=2, cols=2

Output

rows =
     2     2

cols =
     2     2

rows =
     2

cols =
     2

Quick Reference

Remember these tips when using size:

• size(A) returns a vector with rows and columns.
• Use [m, n] = size(A) to get rows and columns separately.
• For multi-dimensional arrays, size(A, dim) returns size along dimension dim.

Key Takeaways

Use size(A) to get the dimensions of matrix A as a vector.

Use [m, n] = size(A) to get rows and columns separately.

Avoid assigning size(A) directly to separate variables without unpacking.

For multi-dimensional arrays, specify the dimension with size(A, dim).

Remember that size works for any array, not just 2D matrices.