Aspect Ratio Calculator
Find the aspect ratio of any width and height, resize an image or video without stretching it, and see the letterbox bars when one ratio has to fit inside another.
Find the ratio
Resize and keep the ratio
≈ marks a listed size that does not reduce to the locked ratio.
Fit or crop one ratio into another
Aspect ratios explained
Common ratios and where they are used
16:9 is the default for TVs, YouTube, laptops and most monitors. 16:10 gives a little extra height and is back on MacBooks and many business laptops. Ultrawide monitors are sold as 21:9, but 2560 × 1080 is really 64:27 and 3440 × 1440 is 43:18. 4:3 is old TVs, iPads and many phone camera sensors, and 3:2 is DSLR photos and Surface screens. Social media leans tall: 9:16 for Reels, TikTok and Shorts, 4:5 for Instagram feed posts, 1:1 for squares. Cinema scope films are about 2.39:1. Print uses paper sizes instead, with A4 at roughly 1:1.414 and 4 × 6 inch photos at 3:2.
Why 1366 × 768 is not exactly 16:9
Type it into the finder and you get 683:384, not 16:9. The 768 rows came from the older 1024 × 768 XGA standard. A true 16:9 width at 768 tall is 1365.3333333333333 pixels, and a panel cannot have a third of a pixel, so makers rounded up to 1366. Some used 1360, which divides by 8 and suited graphics hardware better. Either way the box says 16:9 and the panel is 0.05% off. The same thing happens with 854 × 480 video and with ultrawides labelled 21:9. Nobody will see the difference, but it explains why a calculator says "approximately".
Resizing without stretching
Lock the ratio and type the side you know. The other side is that length multiplied or divided so the pair stays on the ratio, even when the answer is a fraction of a pixel. When the nearest whole-pixel pair differs, it is listed under the result with its own integer gcd, not as the locked ratio. Even numbers are a separate pair for video: H.264 and HEVC with 4:2:0 colour need both sides divisible by 2, and some encoders reject odd sizes. A tie on an odd integer uses the higher even number.
Letterbox, pillarbox and crop
When content is wider than the screen, fitting it adds black bars above and below (letterbox). When it is narrower, bars go on the sides (pillarbox). Picture height for a wider frame is screen width divided by the frame ratio, and each bar is half of the leftover screen height. A 2.39:1 film on a 1920 × 1080 screen is 1920 × 803.347280334728, with bars of 138.326359832636 px each. That is about 25.6% of the screen. Fill mode scales until the bars are gone and crops the overflow instead. That is the trade-off behind "zoom" settings on TVs and phones.
Related tools
Check your display's real resolution with the screen resolution test, measure its physical size with what is my screen size, or turn resolution and diagonal into pixel density with the PPI calculator.
Frequently asked questions
How is the simplified ratio worked out?
It is the greatest common divisor of the width and height you typed, and only when both are whole pixels. 1920 and 1080 become 16:9. A fractional pixel has no integer gcd, so the simplified ratio is a dash and the decimal line is width divided by height. Zero, a negative number, or a non-numeric side is a dash, not Infinity or NaN.
Does resizing keep the ratio?
Yes. The side you type stays as typed, and the other side is that length times the ratio, or divided by it. The result can be a fraction of a pixel, and that fraction is what keeps the ratio. The nearest whole-pixel pair is listed under it with its own reduced ratio, because rounding can change the ratio. It is not labeled as the locked ratio when it differs.
Why is 1366 × 768 not 16:9?
1366 and 768 reduce to 683:384. A 16:9 frame that is 768 px tall is 1365.3333333333333 px wide. 1366 is 0.05% wider at the rounding this page uses for that percent. The page calls a match exact only when the ratios agree, not when they are close.
Is the 21:9 preset the fraction 21/9?
No. 21 divided by 9 is about 2.333:1. The ultrawide preset is 64:27, about 2.370:1, which is the real ratio of 2560 × 1080 and 5120 × 2160. Those panels are sold as 21:9. 3440 × 1440 is 43:18. Results name 64:27 rather than calling that size exactly 21:9.
How are letterbox and pillarbox sizes calculated?
Fit mode keeps the frame inside the screen. When the frame is wider, the width matches the screen and the height is the screen width divided by the frame ratio. Each letterbox bar is half of the leftover height. When the frame is narrower, the height matches and each side bar is half of the leftover width. A 2.39:1 frame on 1920 × 1080 is 1920 × 803.347280334728, and each bar is 138.326359832636 px. Fill mode covers the screen and crops the overflow. A near miss is not treated as the same ratio.
What does the even-pixel option change?
It does not replace the exact size. It adds the nearest positive even width and height. A tie on an odd integer uses the higher even number. H.264 and HEVC with 4:2:0 colour need both sides divisible by 2, and some encoders reject odd sizes. The even pair is reduced on its own, and that ratio can differ from the locked one.