Find the aspect ratio of any size, or the missing width or height, in px, inches or cm
Runs in your browser. Nothing you type is sent anywhere. Updated on 24 Oct 2026.An aspect ratio is the proportion of width to height, written as two whole numbers such as 16:9. Type a width and height for the simplified ratio, or a new width for the matching height: 1920 × 1080 is 16:9, and 1280 wide at 16:9 is 720 high. Inches, cm and pixels at any DPI work. Free; nothing is uploaded.
Type the width and height, or tap a preset such as 16:9, A4 or 4×6 in.
Read the simplified ratio, its decimal form and the nearest standard ratio.
Type a new width or height to get the other side at the same ratio.
Switch the unit to inches, cm or mm and set the DPI to see the size in pixels for print.
Divide the width and the height by their greatest common divisor. For 1920 × 1080 the greatest common divisor is 120, so the ratio is 16:9. Decimal sizes are scaled to whole numbers first: US Letter, 8.5 × 11 inches, becomes 85:110 and then 17:22. The decimal form, width divided by height, is 1.778 for 16:9.
Multiply the new width by the height and divide by the old width: at 16:9, a width of 1280 gives a height of 1280 × 9 ÷ 16 = 720. When the height does not come out whole, the page offers the nearest sizes that keep the ratio exactly, which for 16:9 are widths in steps of 16 pixels.
| Ratio | Common sizes | Typical use |
|---|---|---|
| 16:9 | 1280 × 720, 1920 × 1080, 3840 × 2160 | Video, TVs, laptops |
| 9:16 | 1080 × 1920 | Phone video, stories, reels |
| 4:3 | 1024 × 768, 1600 × 1200 | Older screens, tablets |
| 1:1 | 1080 × 1080 | Square posts, profile pictures |
| 21:9 | 2560 × 1080, 3440 × 1440 | Ultrawide monitors, cinema |
| 1:√2 | A4, 210 × 297 mm | ISO A-series paper |
Every ISO 216 A size has the ratio 1:√2, about 1:1.414, so halving the long side gives the next size with the same shape. A4 is 210 × 297 mm, which simplifies to 70:99, within 0.01% of 1:√2.
One inch is exactly 2.54 cm, and pixels equal inches times the DPI. A 4 × 6 inch photo printed at 300 DPI needs 1200 × 1800 pixels; A4 at 300 DPI is 2480 × 3508. To check whether a photo you already have is big enough, use the Photo Size Calculator; to change a picture's size, use Resize Image.
The aspect ratio of 1920 × 1080 is 16:9. Both sides divide by 120, their greatest common divisor, giving 16 and 9. The same ratio covers 1280 × 720 (HD), 2560 × 1440 (QHD) and 3840 × 2160 (4K UHD), so a video made for one of these sizes scales to the others without black bars.
Multiply the width by 9 and divide by 16. A width of 1280 gives 720, 1600 gives 900 and 1000 gives 562.5, which is not a whole pixel; the nearest exact 16:9 sizes there are 992 × 558 and 1008 × 567. For any other ratio W:H, the height is width × H ÷ W.
Phone-filling stories, reels and TikTok videos use 9:16, usually 1080 × 1920 pixels. Instagram feed posts can be square at 1:1 (1080 × 1080) or portrait at 4:5 (1080 × 1350). YouTube videos are 16:9. Each ratio is a preset on the calculator.
A 4 × 6 inch print at 300 DPI, the usual quality for photos, needs 1200 × 1800 pixels; a 5 × 7 needs 1500 × 2100 and an 8 × 10 needs 2400 × 3000. Multiply each side in inches by the DPI. At 150 DPI half as many pixels are enough for prints viewed from further away.
No. A4 (210 × 297 mm) has the ISO ratio 1:√2, about 1:1.414, while US Letter (8.5 × 11 inches) is 17:22, about 1:1.294. Letter is wider and shorter, so a page designed for one leaves margins on the other. The calculator's paper presets show both ratios side by side.
The size 1366 × 768 simplifies to 683:384, not 16:9: a true 16:9 screen 768 pixels tall would be 1365.33 pixels wide, so makers rounded to 1366. The difference is 0.05%, invisible in practice, and the calculator reports it as close to 16:9 rather than equal.
Formula only: no rates or limits are read from an official source.
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