Ratio Calculator

What a Ratio Is

A ratio compares two amounts - like 3 cups of flour to 2 cups of sugar, written 3 : 2. It does not say how much you have, only the relationship between the parts: keep 3 parts flour for every 2 parts sugar and the recipe tastes the same whether you make a little or a lot.

That is why a ratio can be simplified like a fraction. 12 : 8 and 3 : 2 describe the same mix, just scaled differently - divide both parts by what they share. And two equal ratios form a proportion ($a : b = c : ?$), which lets you scale up or down and find a missing amount. The split bar under the calculator shows the two parts; in proportion mode both bars split the same way, which is exactly what makes the ratios equal.

How It Works

• Simplify: divide both parts by their greatest common divisor.
• Proportion: in $a : b = c : \,?$, the missing value is $\dfrac{b \times c}{a}$.

How to Use It

1. Choose simplify a ratio or solve a proportion.
2. Enter the parts (a third value c appears for proportions).
3. Read the simplified ratio, or the solved proportion.

Worked Examples

Simplifying:

Ratio	Simplest form
12 : 8	3 : 2
10 : 5	2 : 1
9 : 12	3 : 4
2.5 : 5	1 : 2

Solving a proportion:

Proportion	Missing value
3 : 4 = 9 : ?	12
2 : 5 = 6 : ?	15
5 : 2 = 20 : ?	8

FAQ

How do you simplify a ratio?

Divide both parts by their greatest common divisor. For 12 : 8 the GCD is 4, so it simplifies to 3 : 2.

How do you solve a proportion?

In $a : b = c : ?$, the missing value is $\frac{b \times c}{a}$. For 3 : 4 = 9 : ?, that is $\frac{4 \times 9}{3} = 12$.

Can it simplify ratios with decimals?

Yes. It scales the decimals to whole numbers first, so 2.5 : 5 becomes 1 : 2.

What is a ratio?

A ratio compares two quantities, like 3 : 2. It is closely related to fractions, and equal ratios form a proportion.