How to Use This Tool
Enter any two dimensions to get the exact ratio, then use the lower box to resize while keeping the proportions.
The exact ratio and the named one
Dividing both numbers by their greatest common divisor gives the ratio in lowest terms. Sometimes that matches the familiar name — 1920×1080 really is 16:9. Often it does not: 1280×800 reduces to 8:5, which is the same shape as 16:10, just written smaller.
And some dimensions reduce to nothing recognisable. A phone screen at 2532×1170 is 422:195, because it was designed around a camera cutout rather than a broadcast standard. Naming it "roughly 19.5:9" is a convention, not a measurement.
This matters when you assume a ratio and then scale to it. If your source is 1.9% off 16:9 and you force it into a 16:9 frame, everything stretches by 1.9% in one direction. Nobody consciously notices, and faces look subtly wrong.
Rounding is a real decision
Scale 1920×1080 to a width of 1000 and the height is 562.5. Pixels are whole numbers, so you get 562 or 563, and neither is exactly 16:9. That half-pixel is usually irrelevant — but it is why a resized image sometimes has a one-pixel line of background at an edge, and why tiling several resized images can leave gaps.
Where it must be exact, pick dimensions that divide cleanly. For 16:9 that means multiples of 16 and 9: 1920×1080, 1600×900, 1280×720, 640×360 all work without rounding.
The ratios worth knowing
- 16:9 — video, most screens, YouTube. 1.778.
- 4:3 — older screens, many camera sensors, iPad. 1.333.
- 3:2 — 35mm film and most DSLR sensors. 1.5.
- 1:1 — square, social posts.
- 4:5 — vertical social posts; takes the most feed space without being cropped.
- 9:16 — full-screen vertical video.
- 1.91:1 — Open Graph link previews, 1200×630.
- 2.39:1 — anamorphic cinema widescreen.
A note on non-square pixels
Everything here assumes square pixels, which is true of everything digital you are likely to touch. Older broadcast formats did not: DV PAL is 720×576 pixels displayed as 4:3, so the pixels themselves are rectangular and the storage ratio and display ratio differ. If you are working with legacy video and the shape looks wrong, that is usually why.
