Everyday math
Ratio calculator
Simplify a ratio such as 1920:1080, or keep a ratio the same while you resize, for a recipe, a photo, or a map scale.
What this means
- The ratio is 16 : 9.
- Two ratios are equal when A divided by B gives the same number, which is why scaling keeps the shape of a photo or the taste of a recipe.
What if
About this calculator
What this calculator does
It either reduces a ratio to whole numbers with no common factor, or keeps the ratio fixed and solves for a missing fourth value.
How it is calculated
simplify: divide A and B by their greatest common divisor
solve: A / B = C / D, so D = B * C / A
How to read the result
A simplified ratio such as 16 : 9 describes the same shape as 1920 : 1080. A solved D keeps C and D in the same proportion as A and B.
Sources and method
Standard arithmetic with no outside data. The formula is shown under How it is calculated, and unit tests check worked examples, including edge cases.
This page uses arithmetic only, with no outside data.
Questions
What is the ratio of 1920 by 1080?
16 : 9, the common widescreen aspect ratio.
Can ratios use decimals?
Yes. The page scales decimals to whole numbers before simplifying.
How do I scale a recipe?
Use solve mode. A and B are the original amounts of two ingredients, C is the new amount of the first.
Is a ratio the same as a fraction?
Closely related. A : B has the same value as the fraction A / B.