A **ratio **is used to compare two numbers. Ratios are useful for understanding how large one value is compared to another.

For example, suppose A = 40 and B = 10.

To calculate the ratio of A to B we can use the following two step process:

**Step 1**: Find the greatest common divisor (the largest integer that will divide each value)

- The largest value that will divide into both 40 and 10 is
**10**.

**Step 2**: Divide each value by the greatest common divisor and write the result as A:B.

- The ratio of 40 to 10 would be written as
**4:1**.

To calculate the ratio between any two numbers in Excel, we can use the following formula:

=A2/GCD(A2, B2)&":"&B2/GCD(A2, B2)

This particular formula calculates the ratio between the value in cell **A2** to the value in cell **B2**, using the **GCD** function in Excel to automatically find the greatest common divisor between the two values.

The following example shows how to use this function in practice.

**Example: Calculate Ratios in Excel**

Suppose we have the following two lists of values in Excel:

Suppose we would like to calculate the ratio of Value 1 to Value 2 in each row.

We can type the following formula into cell **C2**:

=A2/GCD(A2, B2)&":"&B2/GCD(A2, B2)

The following screenshot shows how to use this formula in practice:

It turns out that the greatest common divisor of 12 and 5 is 1. Thus, when we divide each value by 1 we’re simply left with a ratio of **12:5**.

We can copy and paste this formula in cell **C2** down to every remaining cell in column C to calculate the ratio for the two values in each row:

Here’s how to interpret the results:

- The ratio between 12 and 5 is
**12:5**. - The ratio between 40 and 10 is
**4:1**. - The ratio between 20 and 8 is
**5:2**.

And so on.

**Note**: You can find the complete documentation for the **GCD** function in Excel here.

**Additional Resources**

The following tutorials explain how to perform other common tasks in Excel:

Excel: How to Find Unique Values from Multiple Columns

Excel: How to Match Two Columns and Return a Third