Ratio Calculator Calculators
Simplify ratios, scale them up, and solve for a missing value.
Ratio Calculator is a free online tool that simplify ratios, scale them up, and solve for a missing value. It runs entirely in your web browser using plain JavaScript, so files are processed on your own device and never uploaded to a server. There is no sign-up, no file size limit imposed by the site, no watermark and no paid tier.
- Price
- Free — no account, no quota, no watermark
- Category
- Calculators
- Where it runs
- In your browser, on your device
- Files uploaded
- None
- Technology
- plain JavaScript
- Settings
- 3
- Works offline
- Yes, after the first visit
About Ratio Calculator
Simplification divides both sides by their greatest common divisor, which is why 1920:1080 comes back as 16:9. The scaling field solves the proportion a:b = c:d for the missing fourth value — the same arithmetic behind resizing an image, mixing a solution, or scaling a recipe.
How to use it
- Enter a, b and c (scale a to this).
- Results update the moment anything changes.
The 3 settings
| Setting | What it does | Default |
|---|---|---|
| A | A numeric value. | 16 |
| B | A numeric value. | 9 |
| C (scale A to this) | A numeric value. | 1920 |
Under the hood
| Runs on | plain JavaScript — runs the whole thing |
| Controls | A, B, C (scale A to this) |
Questions
Why does my screen resolution not simplify to a familiar ratio?
Some panels are not exactly 16:9. 1366×768, for instance, reduces to 683:384 — very close to 16:9 but not equal, which is why some content shows a hairline letterbox on those screens.
Is the arithmetic exact?
It uses double-precision floating point — about 15 significant figures, far more than the inputs justify. Displayed rounding is cosmetic; the underlying numbers are not rounded between steps, so chained results do not drift.