Online Tool Store
Aspect Ratio Calculator
Enter an original width and height, then solve for a missing new width or height while keeping the exact same aspect ratio, with the simplified ratio shown. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Original size
New size (leave one blank)
Example shown - enter either the new width or new height, the other is solved automatically.
Aspect ratio
Resulting size
How the aspect ratio calculator works
- Enter your original width and height.
- Enter either a new width or a new height - not both.
- The tool solves the missing dimension so the new size keeps the exact same proportions.
The formula
new height = new width × (original height / original width)
The simplified ratio is found by dividing both the original width and height by their greatest common divisor - for example, 1920 and 1080 share a greatest common divisor of 120, giving 16:9.
FAQ
How do I find a missing dimension?
Enter the original width and height, then enter only the new width or only the new height - the tool solves the missing one so the ratio stays identical.
What does the "aspect ratio" value mean?
It is the original width and height reduced to their simplest whole-number ratio, e.g. 1920×1080 simplifies to 16:9, using the greatest common divisor of both numbers.
Can I use this for print sizes, not just screens?
Yes. The math is unit-agnostic - it works the same for pixels, inches, centimeters, or any other consistent unit.
Why does the result round to whole numbers?
Pixel dimensions must be whole numbers, so the calculated dimension is rounded to the nearest pixel, which can introduce a tiny rounding difference in the exact ratio for unusual sizes.
How we compare
| Feature | Online Tool Store | Manual cross-multiplication | Design software resize panel |
|---|---|---|---|
| Simplified ratio shown automatically | ✓ | ✗ | Sometimes |
| No software install needed | ✓ | ✓ | ✗ |
| Instant, no risk of arithmetic error | ✓ | ✗ | ✓ |
For a quick, error-free proportional resize without opening design software, Aspect Ratio Calculator is the fastest path.