The three ratio questions
To simplify, divide both terms by their highest common factor. 12 : 18 becomes 2 : 3 because both divide by 6.
To share an amount, add the terms to count the parts, divide the amount by that number, then give each side its share of parts.
To find a missing term in A : B = C : ?, multiply B by C and divide by A.
Worked examples
Simplifying 12 : 18 gives 2 : 3.
Sharing 300 in the ratio 12 : 18 means 30 parts, so one part is 10 and the shares are 120 and 180.
In 12 : 18 = 6 : ?, the missing term is 18 x 6 / 12 = 9.
Ratios written with decimals
A ratio such as 1.5 : 2 is scaled up until both sides are whole numbers, giving 3 : 4.
The decimal form is still shown, so you can see how many of the second term there are for each unit of the first.
Inputs for the ratio calculator
What do you want to do?
Choose simplify, share an amount, or find a missing term. The boxes below change to match.
First term (A)
The left-hand number of the ratio. In 12 : 18, type 12.
Second term (B)
The right-hand number of the ratio. It cannot be negative when you are sharing an amount.
Amount to share
Only shown when sharing. The amount is divided into equal parts and split between the two sides.
Known term (C)
Only shown when finding a missing term. It is the first term of the second ratio, matching A.
CALCULATOR QUESTIONS
Ratio calculator questions
How do I simplify a ratio?
Divide both terms by their highest common factor. For 12 : 18 the highest common factor is 6, giving 2 : 3.
How do I share an amount in a ratio?
Add the terms to count the parts, divide the amount by the number of parts, then multiply by each term. Sharing 300 in 12 : 18 gives 120 and 180.
What does a ratio of 2 : 3 mean?
For every 2 parts given to the first side, the second side gets 3. The whole is split into 5 equal parts.
Can a ratio have a zero term?
Yes, such as 0 : 5, which means the first side gets nothing. A ratio of 0 : 0 has no simplest form.