Aspect Ratio Calculator
Calculate the missing width or height to keep an aspect ratio, and simplify any width:height to its smallest ratio.
Original size
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Aspect ratio
Resize keeping ratio (edit either field)
Common ratios reference
| Ratio | Pixels | Use |
|---|---|---|
| 16:9 | 1920×1080 | HD video, YouTube |
| 16:9 | 3840×2160 | 4K UHD |
| 4:3 | 1024×768 | Classic monitor |
| 64:27 | 2560×1080 | Marketed as 21:9 ultrawide |
| 1:1 | 1080×1080 | Instagram post |
| 9:16 | 1080×1920 | Story / Reels / TikTok |
| 2:3 | 1000×1500 | Pinterest pin |
| A4 | 2480×3508 | Print @ 300 DPI |
Brand palette? Color shades generator · resize images: Image splitter · social crop: Screenshot beautifier.
FAQ
What does it do?
Simplifies positive integer pixel dimensions, scales either side with your chosen rounding mode, and outputs CSS aspect-ratio code.
Example?
1920×1080 → 16:9. New width 1280 → height 720, or enter height to get width.
Is 2560×1080 exactly 21:9?
No. Its exact reduced pixel ratio is 64:27. “21:9” is the common ultrawide marketing name.
Can I resize from height?
Yes — edit either New width or New height; the other dimension updates to keep the ratio.
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