Aspect Ratio Calculator

An aspect ratio is the proportional relationship between an image's width and its height, written as W:H. The calculator does two jobs, and both rest on the same piece of school mathematics — the greatest common divisor (GCD).

Simplifying a resolution.To turn a pixel size such as 1920×1080 into a clean ratio, you divide both numbers by their greatest common divisor. Euclid's algorithm finds that divisor by repeated remainder: 1920 = 1080·1 + 840, then 1080 = 840·1 + 240, then 840 = 240·3 + 120, then 240 = 120·2 + 0 — so the GCD is 120. Dividing gives 1920÷120 : 1080÷120 = 16:9. Because this is integer division, the reduced ratio is exact — no rounding error can creep in. The decimal ratio is simply width ÷ height (1.778 here), and orientation follows directly: wider than tall is landscape, taller than wide is portrait, equal is square.

Solving a missing dimension. When you fix a ratio and know one side, the other is a single multiplication. For a known width,height = width × H ÷ W; for a known height,width = height × W ÷ H. Screens use whole pixels, so if the multiplication does not land on an integer the tool shows both the exact fractional value and the rounded pixel value, and warns that the result is not pixel-perfect. A cross-check then recomputes your known side back from the solved side to confirm the ratio is preserved.

Naming the ratio.The reduced decimal is compared against a fixed table of standard ratios. A match within a small tolerance (0.01) is labelled with its common name and source: 16:9 comes from ITU-R BT.709 (HDTV) and BT.2020 (UHDTV); 4:3, 5:4 and 16:10 are VESA display heritage; 1.85:1 (Flat) and 2.39:1 (Scope) are the DCI/SMPTE cinema containers. When the reduced integer ratio matches the standard exactly it is tagged "exact"; when only the decimal matches (for example ultrawide panels that are really 64:27) it is tagged "approx". Finally, the tool lists common resolutions that reduce to the same ratio so you can pick a standard size.

• ITU-R BT.709 — HDTV picture parameters (16:9, 1080p)
• ITU-R BT.2020 — UHDTV parameters (4K/8K, 16:9)
• Digital Cinema Initiatives (DCI) — cinema container ratios (Flat 1.85:1, Scope 2.39:1)
• VESA — display standards (VGA to WQXGA resolutions)
• Euclidean algorithm — the exact GCD reduction method

The named-ratio table and resolution presets were last reconciled against these sources on 2026-07-09. The GCD reduction and dimension-solving maths are standard and version-independent.