A ratio expresses the relative sizes of two or more quantities. This calculator supports three operations: simplifying a ratio to its lowest terms, finding an equivalent ratio by scaling, and solving for a missing value in a proportion (a:b = c:d).

1. Select the mode: Simplify, Equivalent, or Missing Value.
2. Enter the known values.
3. For Missing Value, leave one field blank.
4. Click Calculate.

Simplify 6:9 → GCD(6,9)=3 → 2:3
Equivalent to 2:3 with first term 4 → 4:6
Missing: 2:3 = 8:? → ? = (3×8)/2 = 12

Ratios are used in recipes, maps, scale models, finance and many other fields. A simplified ratio is the most useful form because it shows the relationship in the smallest whole numbers. Proportions (a:b = c:d) are used to scale quantities up or down while maintaining the same relationship.

• Confusing ratios with fractions — 2:3 means 2 parts to 3 parts (5 total), not 2 out of 3.
• Leaving more than one field blank in Missing Value mode.

What is a proportion?

A proportion states that two ratios are equal: a:b = c:d. Cross-multiplying gives a×d = b×c, which allows you to solve for any one unknown value.

Can I use decimals?

Yes for Equivalent and Missing Value modes. For Simplify, the calculator rounds to the nearest integer before finding the GCD.