Aspect Ratio Finder

Find the exact ratio from pixel dimensions

Let W be width and H be height. For whole-number dimensions, calculate g = gcd(W, H). The exact reduced ratio is W ÷ g : H ÷ g. With 1920 × 1080, gcd(1920, 1080) = 120. Dividing both dimensions by 120 gives 16:9.

The decimal value is W ÷ H. Here, 1920 ÷ 1080 = 1.777777…, displayed as 1.7778 when rounded to four decimal places. The colon form preserves the exact integer relationship; the decimal form makes comparison easier.

Separate an exact ratio from the nearest common ratio

A ratio finder should report two different facts. The simplified pair identifies the dimensions exactly. A common-ratio match is a label used for comparison. If W × B equals H × A, the dimensions exactly match A:B. If the products differ, A:B is only a nearby shape.

For 1366 × 768 compared with 16:9, calculate 1366 × 9 = 12,294 and 768 × 16 = 12,288. The products differ by 6, so 1366 × 768 is close to 16:9 but is not exact. Its simplified ratio is 683:384, and its decimal value is about 1.7786.

For 2520 × 1080 compared with 21:9, both cross-products equal 22,680: 2520 × 9 = 22,680 and 1080 × 21 = 22,680. The dimensions simplify to 7:3, which is mathematically equivalent to 21:9. Both labels describe the same exact proportion.

Three-step ratio verification card

1. 1
   Input

   Enter width, height, and an optional DPI for a physical-size check.

2. 2
   Calculate

   Reduce W:H with the greatest common divisor and compare decimal shapes.

3. 3
   Result

   Read the exact ratio, common match, and print dimensions in inches.

Common ratio identification table

The table uses exact arithmetic examples. A decimal displayed with an ellipsis repeats indefinitely. Matching by a rounded decimal alone can hide a small difference, so use cross multiplication to confirm an exact label.

Use DPI after the ratio is identified

DPI does not identify image shape. It converts stored pixels to physical inches. Print width = pixel width ÷ DPI, and print height = pixel height ÷ DPI. A 1920 × 1080 image at 300 DPI measures 1920 ÷ 300 = 6.4 inches by 1080 ÷ 300 = 3.6 inches.

The 16:9 ratio remains unchanged because both axes are divided by the same DPI. At 240 DPI, the same pixels measure 8 × 4.5 inches. The physical size changes, while the pixel pair and aspect ratio stay fixed.

Worked finder examples

For every exact label in the table, cross multiplication produces equal products. The 1366 × 768 row is deliberately labeled near 16:9 because its products differ. This prevents a familiar display name from replacing the exact reduced ratio.