How to use the aspect ratio calculator
- Enter your original width and height (or tap a preset ratio).
- Type the new width and the height fills in automatically — or type a height to get the width.
- The simplified ratio (like 16:9) is shown, with a visual preview of the shape.
Common aspect ratios
16:9 is standard widescreen video (YouTube, TVs). 9:16 is vertical for Reels, TikTok and Stories. 1:1 is the classic square social post. 4:3 is older displays and many camera photos, 3:2 is standard DSLR photography, and 21:9 is ultrawide cinema. Keeping the ratio constant when resizing is what stops images looking stretched or squashed.
Benefits
- Calculates the matching width or height so images never look stretched.
- One-click presets for 16:9, 4:3, 1:1, 9:16, 21:9 and 3:2.
- Shows the simplified ratio plus a visual shape preview.
- Instant and private.
Limitations to know
- It calculates dimensions — it does not resize the actual file.
- Some ratios produce fractional pixels that need rounding.
- It does not crop or pad an image to a new ratio.
Common mistakes to avoid
- Rounding both dimensions independently and drifting off the true ratio.
- Upscaling far beyond the original size and losing quality.
- Using a landscape ratio for a vertical platform like Reels or Stories.
Alternatives
To actually resize a file use the Image Resizer; to change the shape use the Image Cropper.
Last updated: August 2026 · Reviewed by the AI Toolbox editorial team.
Frequently asked questions
How is the ratio simplified?
By dividing both numbers by their greatest common divisor — so 1920×1080 becomes 16:9.
Why do my dimensions come out as decimals?
Some ratios don't divide evenly. Round to the nearest whole pixel — a 1px difference is imperceptible.
Will this resize my image?
No — it calculates the dimensions. Use our Image Resizer to actually resize a file.
Is anything uploaded?
No — it's a calculation done in your browser.