What an aspect ratio is
The aspect ratio of an image or a screen is the relationship between its width and its height, written as two numbers separated by a colon. A 16:9 image is 16 units wide for every 9 units tall, whatever its actual size: 1280 × 720, 1920 × 1080 and 3840 × 2160 are all 16:9. Two pictures with the same ratio can be scaled to each other without cropping or stretching.
The calculator reduces your width and height to the smallest whole numbers (dividing both by their greatest common divisor), and also gives the decimal ratio — width divided by height — which some apps and video editors ask for, such as 1.778 for 16:9 or 2.333 for 21:9.
Common aspect ratios
| Ratio | Decimal | Where you see it |
|---|---|---|
| 1:1 | 1 | square posts, profile pictures |
| 5:4 / 4:5 | 1.25 / 0.8 | 8×10 prints, Instagram portrait posts |
| 4:3 | 1.333 | phone and compact camera photos, iPad |
| 7:5 | 1.4 | 5×7 prints |
| 3:2 | 1.5 | DSLR and mirrorless photos, 4×6 prints |
| 16:10 | 1.6 | many laptop screens |
| 16:9 | 1.778 | HD and 4K video, YouTube, monitors and TVs |
| 2:1 | 2 | wide banners |
| 21:9 | 2.333 | ultrawide monitors, cinema |
| 9:16 | 0.5625 | stories, Reels, TikTok, phone screens held upright |
When your size is not an exact match, the result tells you the nearest of these, so a 1366 × 768 laptop screen is reported as 683:384 with 16:9 as the closest common ratio.
Resize without distortion
The second calculator keeps a ratio while you change the size. Pick a preset (16:9, 4:3, 3:2, 1:1, 21:9 and 5:4, plus the portrait ratios 9:16, 4:5 and 2:3) or type your own ratio — or press “Use the ratio above” to reuse the one you just calculated. Then type a new width to get the matching height, or a new height to get the width. A short table lists common widths for that ratio and flags the ones where the height is not a whole number of pixels, which matters for video encoding.
The formulas are simple: new height = new width × ratio height ÷ ratio width, and new width = new height × ratio width ÷ ratio height.
From numbers to pictures
The calculator works out sizes; the other tools apply them. To see whether a photo is big enough for a print at a given ratio and crop it to 4×6, 5×7 or 8×10, use Photo Print Size; the guide to standard photo print sizes lists the ratio of every common paper size. To get the exact pixel size, ratio and file size of images you already have, use Check Image Size. To fit a picture to a banner or post format without doing the math, the Social Media Image Resizer has presets for LinkedIn, X, YouTube, Instagram and Facebook. Everything runs in your browser and nothing is uploaded.