Aspect Ratio Calculator
Give it a ratio and one dimension and it returns the other, or give it two dimensions and it tells you the ratio they already make. When whole pixels cannot hold the ratio exactly it says so, instead of quietly handing you a number that is slightly wrong.
Widescreen / HDExact: whole pixels hold the ratio precisely
Common ratios
Common aspect ratios and their resolutions
The ratio each platform actually expects, with the pixel dimensions people use most. Cropping to the wrong one is what puts black bars down the side.
| Ratio | Decimal | Typical resolution | Where it is used |
|---|---|---|---|
| 16:9 | 1.778 | 1920 × 1080 | YouTube, HD/4K video, most monitors and TVs |
| 9:16 | 0.563 | 1080 × 1920 | TikTok, Reels, Shorts, Stories (vertical video) |
| 1:1 | 1.000 | 1080 × 1080 | Instagram square posts, profile pictures |
| 4:5 | 0.800 | 1080 × 1350 | Instagram portrait, the tallest feed post allowed |
| 4:3 | 1.333 | 1440 × 1080 | Older monitors, iPad, most compact cameras |
| 3:2 | 1.500 | 6000 × 4000 | Digital SLR sensors, 6×4 inch prints |
| 21:9 | 2.333 | 3440 × 1440 | Ultrawide monitors |
| 2.39:1 | 2.390 | 4096 × 1716 | Anamorphic widescreen cinema |
| 1.85:1 | 1.850 | 3996 × 2160 | Standard theatrical widescreen |
| 5:4 | 1.250 | 1280 × 1024 | Legacy displays, 8×10 inch prints |
Common questions
- Why does 21:9 at 1920 pixels wide not come out exact?
- Because 1920 divided by 21 is 91.43, not a whole number. The height works out to 822.857 pixels, which has to be rounded to 823, and 1920 × 823 is no longer quite 21:9. Most calculators round silently. This one flags it and offers the nearest size that does hold the ratio exactly.
- Why does the tool show 7:3 when I typed 21:9?
- They are the same ratio. 21:9 reduces to 7:3 the same way 4/8 reduces to 1/2. The named label (ultrawide, widescreen, square) is matched on the ratio's value, so it still recognises what you meant.
- What does the even-numbers option do?
- It rounds both dimensions to the nearest even number. H.264 and H.265 encode in 2×2 chroma blocks, so an odd width or height makes many encoders fail outright or pad the frame. If you are producing video, leave it on.
- Can I type a decimal like 1.85 instead of a ratio?
- Yes. Cinema ratios are almost always written as decimals such as 1.85, 2.39 and 2.35, so a bare number is read as that value against 1. It is converted to whole numbers properly rather than rounded, so 2.39 becomes 239:100 and the exact sizes it offers really are exact. 16:9, 16/9, 16x9 and 16 9 all work too.
- What ratio should I use for social video?
- 9:16 for vertical feeds and stories, 1:1 for square posts, 16:9 for standard landscape video, and 4:5 for the tallest still image most feeds will show without cropping.
- What is the difference between 21:9 and 2.39:1?
- 21:9 is 2.333:1, a display standard used for ultrawide monitors. 2.39:1 is the anamorphic cinema standard and is slightly wider. They look similar but are not interchangeable. A 2.39:1 master letterboxed onto a 21:9 display still leaves thin bars.
- Can I get the CSS or FFmpeg form?
- Yes. Each result includes a copyable aspect-ratio declaration for CSS and a scale filter argument for FFmpeg, so you can paste the value straight into a stylesheet or a command.
Exact. Ratios are reduced with integer arithmetic, and where a target dimension is not a whole number of pixels the tool says so rather than rounding silently. A half-pixel is a real cause of blurry output.