Our new Aspect Ratio Calculator has two modes and a detail most calculators skip entirely.
- Ratio + one dimension — enter any ratio like 16:9, plus a known
width or height, and get the missing dimension instantly:
otherDim = knownDim × (ratioOther / ratioKnown). - Compare two sizes — paste in two full sizes (say, 1920×1080 and 1280×720) and see both reduced to their simplest ratio via their greatest common divisor, so you know at a glance whether they’re really the same shape. (They are: both reduce to 16:9.)
- Six common ratio presets — 16:9, 4:3, 1:1, 21:9, 3:2, and 9:16, one tap away.
- Paper size presets that are actually correct for where you are — the English page ships US customary sizes (Letter, Legal, Tabloid) because the US is one of the only countries that never adopted the international ISO 216 standard. The Spanish, Italian, and Greek versions of this page ship the ISO A4, A3, and A5 sizes used almost everywhere else instead — a real, honest difference in which paper comes out of the printer, not a cosmetic translation choice.
Fun fact buried in the explainer: A4’s 210×297mm gives a ratio of 297/210 = 1.4142857…, which matches √2 (1.41421356…) to four decimal places — the reason an A-series sheet folded exactly in half produces the next size down at the identical proportions.
Everything computes instantly in your browser; nothing you type is ever sent anywhere.