How to use the Ratio Calculator
- Choose Solve (find a missing value) or Simplify.
- Enter the ratio A : B.
- For Solve, enter C — the answer is the value that keeps the same ratio.
What does this tool do?
Ratios compare quantities: 3 parts water to 1 part concentrate, a 16:9 screen, or 4 servings scaled to 10. Solving A : B = C : D finds D = B × C ÷ A.
Simplifying divides both sides by their greatest common factor, and handles decimals by scaling them up to whole numbers first (1.5 : 2.5 becomes 3 : 5).
Why use it?
- Scale recipes and mixtures without errors.
- Work out image and video sizes for an aspect ratio.
- Reduce ratios to their simplest form.
Example: resizing an image
A 4 : 3 image needs to be 1,920 pixels wide. Solve 4 : 3 = 1920 : ?. The height is 3 × 1920 ÷ 4 = 1,440 pixels.
The formula
A : B = C : D → D = B × C ÷ A
Simplified A : B = (A ÷ GCF) : (B ÷ GCF)
Privacy
The calculation happens instantly in your browser. The numbers you enter are not sent to our servers or saved. There's no account to create and nothing to install.
Frequently asked questions
Is a ratio the same as a fraction?
They're related but not identical. A ratio of 2 : 3 means 2 parts to 3 parts, so the first part is 2/5 of the total, not 2/3.
Last reviewed by the M2Toolkit team.