Ratio Calculator

Solve ratio problems instantly with our free ratio calculator. Find a missing value in a proportion, simplify a ratio to its lowest terms, or scale a ratio up or down — all in one tool. Perfect for students, cooks, builders, and anyone working with proportions.

How Ratios and Proportions Work

A ratio compares two quantities (e.g., 3:4). A proportion states that two ratios are equal: A:B = C:D. To solve for a missing value, use cross-multiplication: A × D = B × C. To simplify a ratio, divide both numbers by their Greatest Common Divisor (GCD).

Real-World Examples

• Scaling a recipe: If 3 cups flour serves 4 people, how much flour for 10 people? 3:4 = ?:10 → 7.5 cups
• Map scale: If 1 inch = 50 miles, how many inches for 175 miles? 1:50 = ?:175 → 3.5 inches
• Simplify 24:36 → GCD is 12 → simplified to 2:3

Frequently Asked Questions

What is a ratio?

A ratio is a comparison of two quantities by division. The ratio 3:5 means "3 for every 5," and can also be written as the fraction 3/5 or 0.6. Ratios are used in recipes, maps, finance, and countless everyday situations.

How do I solve a proportion?

Use cross-multiplication. If A:B = C:D, then A × D = B × C. Rearrange to solve for the unknown. For example: 2:5 = 8:? → 2 × ? = 5 × 8 → ? = 40 ÷ 2 = 20.

How do I simplify a ratio?

Find the Greatest Common Divisor (GCD) of both numbers and divide each by it. For 12:8, GCD is 4, so 12÷4 : 8÷4 = 3:2. The simplified ratio 3:2 represents the same proportion as 12:8.

What is the difference between a ratio and a fraction?

A fraction represents a part of a whole (e.g., ¾ means 3 out of 4 parts). A ratio compares two separate quantities (e.g., 3:4 means 3 of one thing for every 4 of another). They're related but used in different contexts.

What is a 1:1 ratio?

A 1:1 ratio means both quantities are equal — for every 1 unit of one thing, there is 1 unit of the other. In photography, a 1:1 ratio means the image on the sensor is the same size as the subject (macro photography).