Ratio Calculator

Simplify a ratio to lowest terms, or solve a proportion for a missing value.

Runs in your browser — nothing is sent or saved.

How to use the ratio calculator

  1. Choose to simplify a ratio or solve a proportion.
  2. To simplify, enter the two parts of the ratio.
  3. To solve a proportion, fill in three values and leave one blank.
  4. Read the result, shown in lowest terms.

Simplifying a ratio

A ratio compares two quantities, like 8 to 12. To simplify it, you divide both parts by their greatest common factor, which gives the same ratio in its smallest whole numbers. For 8 to 12 the greatest common factor is 4, so it reduces to 2 to 3. This ratio calculator, a ratio simplifier at heart, does that reduction exactly and also shows equivalent ratios, the ratio to fraction form, and a decimal.

Solving a proportion

A proportion says two ratios are equal, written A : B = C : D. If you know three of the four values, you can solve for the missing one using cross-multiplication: A times D equals B times C. Enter three numbers, leave one blank, and the tool solves it. This is how you scale a recipe, a map distance, or a mixture up or down.

A worked example

Simplify 18 to 24. The greatest common factor of 18 and 24 is 6. Dividing both by 6 gives 3 to 4, so 18 : 24 equals 3 : 4 in lowest terms. As a fraction that is 3/4, and as a decimal 0.75.

FAQ

How do I simplify a ratio?

Divide both parts by their greatest common factor. The tool does this for you and shows the ratio in lowest terms, plus the fraction and decimal forms.

How do I solve a proportion?

Set the two ratios equal, A : B = C : D, then cross-multiply so A times D equals B times C. Enter three of the values and leave the unknown blank, and the tool solves it.

Can I use decimals in a ratio?

Yes. The tool scales decimals to whole numbers before reducing, so 1.5 : 3 simplifies to 1 : 2.

What is the difference between a ratio and a fraction?

A ratio compares two quantities and a fraction is one number, but they are closely linked: the ratio A : B is the same information as the fraction A/B. The tool shows both.

Is my information private?

Yes. Everything is calculated in your browser and nothing you enter is uploaded or saved.