Summary

To generate the ratio of two numbers to each other (e.g. 4:3, 16:9, etc.), you can do using division, the GCD function, and concatenation. In the generic form of the formula (above) num1 represents the first number (the antecedent) and num2 represents the second number (the consequent).

In the example, the active cell contains this formula:

=B4/GCD(B4,C4)&":"&C4/GCD(B4,C4)

Note: the GCD function only works with integers.

Generic formula

=num1/GCD(num1,num2)&":"&num2/GCD(num1,num2)

Explanation 

This formula looks complicated, but, at the core, it is quite simple, and created in two parts like so:

= (formula for number1) &":"& (formula for number2)

On the left, the GCD function is used to calculated the greatest common divisor (GCD) of the two numbers. Then the first number is divided by the GCD. On the right, the same operations are performed with the second number.

Next, the result of the right and left operations are joined together using concatenation, with the colon (":") as a separator. So, altogether, we have:

=B4/(GCD(B4,C4)) &":"& C4/GCD(B4,C4)
=1280/(GCD(1280,720)) &":"& 720/GCD(1280,720)
=1280/80 &":"& 720/80
=16 &":"& 9
=16:9

Note that the final result of this formula is a text value.

Related functions

Excel GCD function

GCD Function

The Excel GCD function returns the greatest common divisor of two or more integers. The greatest common divisor is the largest integer that goes into all supplied numbers without a remainder. For example, =GCD(60,36) returns 12.
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Dave Bruns

Hi - I'm Dave Bruns, and I run Exceljet with my wife, Lisa. Our goal is to help you work faster in Excel. We create short videos, and clear examples of formulas, functions, pivot tables, conditional formatting, and charts.

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