MMULT Function

Summary

MMULT returns the matrix product of two arrays. Instead of multiplying cells one by one in the usual spreadsheet way, it multiplies rows from the first array by columns from the second array and adds those products together.

This is why the function is useful for weighted scores, coordinate work, and matrix checks. It can do a lot in one formula, but the shape of the inputs has to make sense first.

MMULT is useful because matrix multiplication is not the same as cell-by-cell multiplication. It combines rows and columns according to matrix rules, which makes it valuable in advanced models where one block of numbers transforms or summarizes another.

Syntax

=MMULT(array1, array2)

The number of columns in array1 must match the number of rows in array2. Microsoft also notes that MMULT returns #VALUE! when the dimensions do not line up or when the arrays contain text or empty cells.

Arguments

• array1 - Required. The first numeric array.
• array2 - Required. The second numeric array.

MMULT vs Other Multiplication Options

Not every multiplication task needs MMULT. It is best when you actually want matrix behavior, not just basic arithmetic.

Using MMULT

The first thing to check is the dimensions. If the first array is 3x2 and the second array is 2x2, the multiplication works. If the first array is 3x2 and the second is 3x2, it does not. That shape check matters more than the actual numbers when you are starting out.

Once the dimensions line up, MMULT becomes very practical. You can use it for scoring models, for verifying matrix inverses, or for compact formulas that would otherwise take a lot of helper cells. It is also a good example of why matrix formulas feel different from normal Excel formulas. The result is often a whole range, not one cell.

Example 1 - Multiply two 2x2 matrices

This is the standard starting example. Both arrays are square, and the inner dimensions match, so the multiplication is valid.

This is useful because it shows the basic matrix-multiplication setup without extra complications. The learner can focus on the rule that makes the formula work at all.

=MMULT(B2:C3,E2:F3)

Example 2 - Multiply a row by a matrix

A 1x2 row can multiply a 2x2 matrix because the inner dimension is still 2. The result comes back as a 1x2 array.

This helps show that MMULT is not only for square matrices. Different shapes can still work as long as the inside dimensions line up correctly.

=MMULT(B2:C2,E2:F3)

Example 3 - Predict the result size

If the first array is 3x2 and the second is 2x2, the output will be 3x2. Getting comfortable with that pattern makes MMULT much easier to use.

This is one of the most helpful habits in matrix work because it trains the learner to think about output shape before typing the formula.

=MMULT(B2:C4,E2:F3)

Example 4 - Combine MMULT with TRANSPOSE

Sometimes the array shape you need is not already there. TRANSPOSE can flip it so the multiplication works.

This makes the example practical because shape problems are common in real sheets. TRANSPOSE can often fix the layout without changing the source data itself.

=MMULT(TRANSPOSE(B2:B3),B2:B3)

Conclusion Recap

MMULT is easiest to understand when you focus on shape before numbers. This lesson kept showing that the formula only works when the inner dimensions match, so the first real skill is learning to check the matrix sizes before you even type the formula.

Once that part is clear, the examples make the function feel more practical. MMULT can handle weighted scoring, matrix checks, and nested formulas with TRANSPOSE, but the same core rule stays in place every time: the dimensions have to line up.

• Main job: MMULT returns the matrix product of two numeric arrays.
• Key rule: Columns in the first array must match rows in the second array.
• Typical error: #VALUE! shows up when dimensions do not line up or the arrays contain text or blanks.
• Result shape: Rows come from the first array, columns come from the second.
• Helpful partner: TRANSPOSE is often useful when the orientation is wrong.