Aspect Ratio Calculator
| Common sizes at this ratio | Width | Height |
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Why the shape matters more than the size
An aspect ratio describes proportion, not dimensions. 1920×1080 and 1280×720 are the same shape, so one scales to the other cleanly. Change width and height by different amounts and everything inside stretches — faces widen, circles become ovals, text thickens. Setting one dimension and taking the other from the ratio is what prevents that.
The ratios worth knowing
- 16:9 — video, YouTube, nearly every modern screen.
- 9:16 — vertical video for phones: Reels, Shorts, Stories.
- 1:1 — the square post.
- 4:5 — the taller feed image, which occupies more screen than a square.
- 4:3 — older screens, many camera sensors, most projectors.
- 3:2 — 35mm film and most DSLR sensors.
- 21:9 — cinematic widescreen.
Two things that catch people out
Odd numbers. Many video encoders require both dimensions to be even, and some want multiples of four. If the answer comes out odd, adjust by one pixel rather than letting the encoder decide.
Cropping is not scaling. Making a 16:9 photo into a 1:1 post means cutting parts away, not squeezing. Work out the ratio first, then crop deliberately so you choose what is lost.
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Frequently Asked Questions
The relationship between width and height, independent of size. 16:9 means sixteen units across for every nine down — a 1920×1080 screen and a 3840×2160 screen are both 16:9, and anything you scale between them stays the right shape.
Because the width and height were changed by different amounts. Set one dimension here and take the other from the answer, and the shape is preserved.
Switch to "what ratio is this" and put in the pixel dimensions. The ratio is reduced to its simplest whole numbers, and the nearest well-known ratio is named where there is one.
Because not every size divides evenly. The rounded figure is shown alongside the exact one — round rather than truncate, and check that the result is even if you are encoding video, since many codecs require it.
16:9 for video and most screens, 9:16 for phone-first vertical video, 1:1 for a square post, 4:5 for a taller feed image, 4:3 for older screens and many camera sensors, 21:9 for cinematic widescreen.