The Ratio Calculator reduces any two-term ratio to its simplest whole-number form and solves proportions when one value is missing. Switch to Simplify to enter A and B and instantly see A:B reduced by their greatest common divisor, like turning 8:12 into 2:3. Switch to Solve proportion, pick which of the four terms in A:B = C:D is unknown, fill in the other three, and the tool cross-multiplies to find it. It is useful for scaling recipes, converting map scales, mixing ratios, splitting shares, and checking homework or spreadsheet formulas. Built for students, cooks, designers, and anyone who needs a quick, accurate ratio without doing the arithmetic by hand. Everything runs locally — your figures never leave your device.
Features
Simplify any ratio A:B to lowest terms using the greatest common divisor
Solve a proportion A:B = C:D for any one missing term
Choose which of the four proportion terms is unknown with one click
Accepts decimal inputs like 1.5:2 and simplifies them correctly
Clear error messages for invalid, negative, or incomplete input
Copy the simplified ratio or the solved value in one click
Instant recalculation as you type — no submit button needed
Runs entirely in your browser with no numbers sent anywhere
How to use the Ratio Calculator
Choose Simplify ratio or Solve proportion
For Simplify, enter the two ratio terms A and B
For Solve proportion, pick the unknown term and fill in the other three
Read the result and copy it with the copy button
Example
Input
8:12
Output
2:3
Dividing both terms of 8:12 by their greatest common divisor (4) gives the simplified ratio 2:3.
Common errors & troubleshooting
Simplify shows an error even though the numbers look fine. — Both ratio terms must be 0 or greater — negative values are not valid ratio terms, so remove any minus sign.
Solve proportion says to fill in exactly three terms. — A proportion needs three known values to solve for the fourth — pick the unknown term first, then make sure the other three fields all have a number.
The proportion cannot be solved. — This happens when the required denominator is zero, for example solving A:0 = C:D — check that the term you are dividing by is not zero.
A decimal ratio like 1.5:2 doesn't simplify the way expected. — The Ratio Calculator scales decimals to whole numbers before reducing, so 1.5:2 correctly becomes 3:4 — the same ratio, just in integer form.
Frequently asked questions
What does the Ratio Calculator do?
It simplifies a ratio like 8:12 to its lowest terms (2:3) and solves proportions of the form A:B = C:D when one of the four terms is unknown, using cross-multiplication.
How does the Ratio Calculator simplify a ratio?
It finds the greatest common divisor of both terms and divides each term by it, the same method as reducing a fraction, so 8:12 becomes 2:3.
Can the Ratio Calculator solve a proportion for any of the four terms?
Yes. In Solve proportion mode you pick which of A, B, C, or D is unknown, and the calculator finds it from the other three using A × D = B × C.
Does the Ratio Calculator work with decimal ratios?
Yes. Enter decimals like 1.5:2 and the calculator scales both terms to whole numbers before simplifying, so the reduced ratio is still exact.
Is a ratio the same as a fraction?
A ratio A:B and the fraction A/B represent the same relationship. Use the Fraction Calculator if you need to add, subtract, or convert fractions directly.
Are my numbers uploaded when I use the Ratio Calculator?
No. The Ratio Calculator runs entirely in your browser. The values you type are never uploaded and stay on your device.
Related tools
Fraction Calculator — Add, subtract, multiply and divide fractions and simplify the result.
Percentage Calculator — Solve percentage problems: X% of Y, X is what % of Y, and percent change.
GCF Calculator — Find the greatest common factor of two or more integers with the steps.
LCM Calculator — Find the least common multiple of two or more integers with the steps.
Rounding Calculator — Round numbers to decimals, significant figures or the nearest multiple.