Aspect Ratio Calculator Calculators
Scale dimensions while keeping the same proportions.
Aspect Ratio Calculator is a free online tool that scale dimensions while keeping the same proportions. 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
- 4
- Works offline
- Yes, after the first visit
About Aspect Ratio Calculator
The ratio is reduced with the greatest common divisor, so 1920×1080 shows as 16:9 and 3840×2160 shows as the same. Leave either new dimension at zero and it solves for the other, preserving proportions exactly — which is the arithmetic behind every "constrain proportions" checkbox you have ever ticked.
How to use it
- Enter original width, original height and new width.
- Adjust the remaining 1 setting if the defaults do not fit your case.
The 4 settings
| Setting | What it does | Default |
|---|---|---|
| Original width | A numeric value. | 1920 |
| Original height | A numeric value. | 1080 |
| New width | Leave 0 to solve from height. | 1280 |
| New height | A numeric value. | 0 |
Under the hood
| Runs on | plain JavaScript — runs the whole thing |
| Controls | Original width, Original height, New width, New height |
Questions
Why do I get an odd ratio like 683:384?
Because the numbers genuinely do not reduce to anything tidy. 1366×768 is the classic example: marketed as 16:9, actually a fraction off, which is why it sometimes letterboxes.
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.