Ratio Calculator
Simplify ratios and solve proportions instantly.
How to use
- 1 Enter two whole numbers to see the simplified ratio, its decimal and the divisor used.
- 2 For a proportion, fill three of the a : b = c : d boxes.
- 3 Leave exactly one box blank and the missing value is solved automatically.
- 4 Copy the simplified ratio or the solved answer with one click.
About Ratio Calculator
The Ratio Calculator handles the two everyday jobs people reach for ratios to do: simplifying them and solving proportions.
Type two whole numbers and the simplifier divides both by their greatest common divisor to give the cleanest equivalent ratio — turning 8 : 12 into 2 : 3, or 1920 : 1080 into 16 : 9 — and it also shows the decimal value and the divisor it used so you can see the working.
Negative terms are tidied so the sign sits on the first term, and impossible cases like a zero second term are flagged rather than silently producing nonsense.
The proportion solver answers the classic "fill in the blank" question.
Enter a : b = c : d with exactly one box left empty and it cross-multiplies to find the missing value — perfect for scaling a recipe, resizing an image while keeping its aspect ratio, converting map distances, mixing paint or working out unit pricing.
It guards against division by zero and tells you which term it solved.
Both calculations update live as you type, and everything runs locally in your browser.
Nothing you enter is uploaded, logged or stored, so the tool is fast, private and keeps working without a connection once the page has loaded.
FAQ
How does the simplifier reduce a ratio?
It divides both terms by their greatest common divisor (GCD), which is the largest number that divides both exactly, giving the smallest equivalent whole-number ratio.
How do I solve for a missing term?
Enter three of the four values in a : b = c : d and leave the unknown one blank. The tool cross-multiplies (a×d = b×c) to compute it.
Can it handle decimals in proportions?
Yes. The proportion solver accepts decimal inputs. The simplifier, however, needs whole numbers because ratios are reduced using integer division.