How do I simplify a ratio?

Divide both sides by their greatest common divisor. For 8:12 the greatest common divisor is 4, so the ratio simplifies to 2:3. The calculator does this for you and handles decimals by scaling them to whole numbers first.

How do I solve A:B = C:? for the missing number?

Cross-multiply: the missing value is B × C ÷ A. So for 2:3 = 10:?, the answer is 3 × 10 ÷ 2 = 15. Enter the three known values in the solve mode and the fourth is filled in.

What does scaling a ratio mean?

Scaling multiplies both sides by the same factor, which keeps the proportion the same while changing the actual amounts. Scaling 2:3 by 4 gives 8:12. It is how you turn a recipe or mix ratio into real quantities for a chosen batch size.

Does this work offline and is anything sent to a server?

The calculation runs entirely in your browser, so nothing you type is sent anywhere, and once the page has loaded it keeps working with no connection. There is no sign-up and no limit on how many calculations you make.

Ratio Calculator

Simplify a ratio to its lowest whole-number terms, solve a proportion like A:B = C:? for the missing value, or scale a ratio up or down by a factor. Type the numbers and read the answer instantly. A free ratio calculator that runs in your browser.

Exact, step-by-step answers
100% free
No sign-up, no app
Instant as you type
Works offline after first load

Read the guide: How to Simplify a Ratio

Simplified ratio

2 : 3

8 : 12 divided by their greatest common divisor

How to use it

1
Choose what to do

Simplify a ratio, solve for a missing term, or scale a ratio. Pick the mode that matches your question.
2
Enter the values

Fill in the two or three numbers for that mode. Decimals are fine for simplifying.
3
Read the result

See the simplified ratio, the missing value, or the scaled ratio, updated as you type.

When it comes in handy

Recipes and mixes

Scale a 2:1 ratio of flour to water up to the batch size you need, keeping the proportion exact.

Maps and models

Solve a scale like 1:50 to find a real-world or model measurement from the other.

Sharing and splits

Simplify a ratio such as 8:12 to 2:3 to see the cleanest way to divide something.

Instant, exact & 100% in your browser

The maths runs right here in your browser, with fractions and whole numbers kept exact rather than rounded along the way. Nothing you type is sent to a server, there is no sign-up and no limit, and once the page has loaded it keeps working even with no connection.

Frequently asked questions

How do I simplify a ratio?: Divide both sides by their greatest common divisor. For 8:12 the greatest common divisor is 4, so the ratio simplifies to 2:3. The calculator does this for you and handles decimals by scaling them to whole numbers first.
How do I solve A:B = C:? for the missing number?: Cross-multiply: the missing value is B × C ÷ A. So for 2:3 = 10:?, the answer is 3 × 10 ÷ 2 = 15. Enter the three known values in the solve mode and the fourth is filled in.
What does scaling a ratio mean?: Scaling multiplies both sides by the same factor, which keeps the proportion the same while changing the actual amounts. Scaling 2:3 by 4 gives 8:12. It is how you turn a recipe or mix ratio into real quantities for a chosen batch size.
Does this work offline and is anything sent to a server?: The calculation runs entirely in your browser, so nothing you type is sent anywhere, and once the page has loaded it keeps working with no connection. There is no sign-up and no limit on how many calculations you make.