Ratio Calculator
Use this free Ratio Calculator to calculate your Ratio result instantly and accurately.
Proportion A:B = C:D
Result
What is a Ratio Calculator?
A ratio calculator simplifies ratios and solves for missing terms in proportional relationships. It handles ratio comparisons, scaling, and finds unknown values using cross-multiplication.
How to calculate ratios manually (the formula)
To simplify a ratio a:b, divide both parts by their greatest common factor (GCF). To solve for a missing value, set up a/b = c/d and cross-multiply: ad = bc.
Example calculation
Simplify 12:18. The GCF of 12 and 18 is 6. Divide both by 6: 12 ÷ 6 : 18 ÷ 6 = 2:3. To solve x/5 = 8/10, cross-multiply: 10x = 40, so x = 4.
Common mistakes
- Dividing by the wrong number — Always divide both parts of the ratio by the GCF, not just one side.
- Reversing the ratio order — The ratio a:b is not the same as b:a. Keep the order consistent.
- Forgetting to simplify fully — Check that no common factor remains between the two numbers after simplifying.
Frequently asked questions
What is a ratio?
A ratio compares two or more quantities, showing their relative sizes. It is often written as a:b or a/b.
How do you simplify a ratio?
Divide both parts by their greatest common factor (GCF). For example, 6:9 simplifies to 2:3 by dividing both by 3.
How do you solve for a missing value in a ratio?
Set up a proportion a:b = c:d and cross-multiply. If d is unknown, d = bc/a.
Can ratios be expressed as fractions?
Yes. The ratio a:b is equivalent to the fraction a/b. Both compare the first quantity to the second.
What is the difference between a ratio and a proportion?
A ratio compares two quantities. A proportion states that two ratios are equal.
How are ratios used in real life?
Ratios appear in recipes (ingredient proportions), maps (scale ratios), finance (debt-to-income ratio), and many other everyday situations.