Aspect ratio calculator
Work out the missing width or height for any ratio, or reduce a pixel size to its ratio — 16:9, 4:3, 4:5, 9:16 and more. Runs locally in your browser.
Type a width or a height — the other side is filled in automatically.
Common aspect ratios and resolutions
| Ratio | Typical resolutions (px) | Used for |
|---|---|---|
| 16:9 | 1280 × 720 · 1920 × 1080 · 2560 × 1440 · 3840 × 2160 | Video, YouTube, monitors, TV |
| 9:16 | 1080 × 1920 · 720 × 1280 | Stories, Reels, TikTok, phone screens |
| 4:3 | 1024 × 768 · 1600 × 1200 · 2048 × 1536 | Older monitors, compact cameras, iPad |
| 3:2 | 1080 × 720 · 3000 × 2000 · 6000 × 4000 | DSLR / full-frame photos, 10 × 15 cm prints |
| 1:1 | 1080 × 1080 · 800 × 800 | Instagram square, profile pictures |
| 4:5 | 1080 × 1350 | Instagram portrait feed post |
| 1.91:1 | 1200 × 630 · 1080 × 566 | Facebook / Open Graph link images |
| 21:9 | 2560 × 1080 · 3440 × 1440 | Ultra-wide monitors, cinematic |
| 2:3 | 1000 × 1500 | Pinterest pins, portrait prints |
What an aspect ratio is
An aspect ratio describes the proportion between an image’s width and height, written as two numbers separated by a colon. A 16:9 frame is 16 units wide for every 9 units tall — whether that is 1280 × 720 or 3840 × 2160 makes no difference to the shape. The ratio tells you nothing about size or resolution; it only fixes the outline.
That is why the same ratio comes up everywhere: every YouTube video, every modern monitor and every TV shares 16:9, so a thumbnail made at 1280 × 720 scales cleanly to any of them. Getting the ratio right before you resize or crop is what prevents black bars, stretched faces and unexpected cropping on upload.
How the calculator works
Choose a preset or type your own ratio, then enter either a width or a height. The calculator keeps the proportion and fills in the other side, rounding to whole pixels. Under the hood it is a simple cross-multiplication: height = width × (ratio height ÷ ratio width). A 16:9 image that is 1600 px wide is therefore 1600 × 9 ÷ 16 = 900 px tall.
The second mode goes the other way. Enter an existing width and height — say 1440 × 900 — and it reduces them with the greatest common divisor to the simplest ratio (8:5, better known as 16:10), shows the decimal factor (1.6:1) and names the closest standard ratio. That is handy when a photo from a camera or a screenshot needs to fit a platform preset.
Which ratio for which platform
- 16:9 — YouTube videos and thumbnails (1280 × 720), presentation slides, most displays.
- 9:16 — vertical video and stories: TikTok, Instagram Reels and Stories, YouTube Shorts (1080 × 1920).
- 4:5 — Instagram’s tallest feed format (1080 × 1350); it takes up the most screen space in the feed.
- 1:1 — square posts and profile pictures (1080 × 1080).
- 1.91:1 — link previews and Open Graph images for Facebook, LinkedIn and X (1200 × 630).
- 3:2 — the native ratio of most full-frame and APS-C cameras, and of a 10 × 15 cm print.
- 4:3 — compact cameras, iPads and older monitors; also the standard for many phone camera sensors.
When a photo has to appear in several of these, crop it once per ratio rather than letting each platform auto-crop — the social media resizer does that from a single upload.
Resizing vs cropping
Resizing keeps every pixel but changes the count; it cannot change the ratio without distorting the picture. Cropping removes pixels from the edges and is the only way to move from one ratio to another without stretching. In practice you crop to the target ratio first, then resize to the exact pixel size the platform wants. Both tools run locally on imagenimble, so the original never leaves your device.
Privacy by design
All processing happens inside your browser. Your files never reach a server — there is nothing to store, transmit or share.
Learn more in our privacy policyFrequently asked questions
Multiply the width by 9 and divide by 16. For 1920 px that gives 1920 × 9 ÷ 16 = 1080 px. The calculator does this automatically for any ratio.
4:5. Dividing both numbers by their greatest common divisor (270) gives 4:5, the portrait format Instagram uses for feed posts.
16:10 (reduced form 8:5), a slightly taller shape than 16:9 that is common on laptops and productivity monitors.
Only by distorting the image or adding borders (letterboxing). To keep the picture natural, crop to the new ratio and then resize.
No. The calculation runs entirely in your browser; nothing is sent to a server.