Free Aspect Ratio Calculator
Work out ratios and resize keeping proportions.
What is the Aspect Ratio Calculator?
Resize an image or video by eye and you'll almost always stretch or squash it — a face goes wide, a logo goes tall. Keeping the aspect ratio fixed is what stops that, and it's just a bit of arithmetic that's easy to get wrong under deadline.
This aspect ratio calculator finds the exact ratio of any dimensions and computes the matching size when you scale one side, so proportions stay perfect.
Last updated: Aug 13, 2026
What does this tool do?
You enter an original width and height and the tool reduces them to a simplified ratio (like 16:9) and a decimal value.
Then, in the resize section, you type a new width or height and it fills in the other dimension to keep the exact same proportions.
Key features
Simplified ratio
Reduces any size to its lowest terms.
Decimal value
The ratio as a precise number too.
Proportional resize
Enter one side, get the other.
Common presets
16:9, 4:3, 1:1, 21:9 and more.
Instant & private
Runs entirely in your browser.
Example
Common use cases
- Video editors — Keep footage at 16:9 or 21:9.
- Designers — Resize graphics without distortion.
- Photographers — Crop and export at set ratios.
- Developers — Compute responsive image dimensions.
- Social media managers — Fit platform-specific sizes.
- Marketers — Size banners and thumbnails correctly.
- Presenters — Match slides to 16:9 or 4:3.
- Anyone resizing media — Scale without stretching.
Benefits
- It stops images and video from stretching.
- It gives the exact matching dimension every time.
- It reduces any size to a clean ratio.
- Presets cover the ratios you use most.
Tips
- 16:9 is standard for video and most screens.
- 1:1 (square) suits many social feeds; 9:16 for vertical video/stories.
- Round to whole pixels — you can't have a fraction of one.
- Match the ratio to the platform's recommended size.
- Lock the ratio in your editor when dragging to resize.
- Crop to change ratio; scale to keep it.
- For print, remember DPI is separate from aspect ratio.
- Keep source files large and scale down, not up.
Common mistakes to avoid
Resizing without locking the ratio
Fix: Enter one dimension and let the other follow so nothing stretches.
Scaling up small images
Fix: Upscaling blurs — start from a larger source and scale down.
Confusing ratio with resolution
Fix: 1280×720 and 1920×1080 are both 16:9 — ratio is the shape, resolution is the size.
Wrong ratio for the platform
Fix: Check the target's recommended ratio before exporting.
How it works
- 1
Enter original size
Width and height, or pick a preset.
- 2
See the ratio
Simplified ratio and decimal value.
- 3
Resize
Type one new dimension to get the other.
Frequently asked questions
The simplified aspect ratio (like 16:9) and decimal value of a width and height, and the matching dimension when you resize one side.
Enter your original width and height, then type a new width or height — the other value fills in automatically to preserve the ratio.
The simplified aspect ratio (like 16:9) and decimal of a width and height, plus the matching dimension when you resize one side.
Enter your original width and height, then type a new width or height — the other value fills in to preserve the ratio.
Aspect ratio is the shape (16:9); resolution is the pixel size (1920×1080). Many resolutions can share one ratio.
16:9 (widescreen), 4:3 (classic), 1:1 (square), 21:9 (ultrawide) and 9:16 (vertical).
Scaling down is fine; scaling up beyond the source resolution reduces sharpness.
No. The calculation runs entirely in your browser.
Conclusion
An aspect ratio calculator keeps every resize proportional, so images and video never stretch. Pair it with the image resizer to apply the dimensions you work out here.