Simplifying a ratio
Divide both the width and the height by their greatest common divisor (GCD). For 1920 × 1080 the GCD is 120, so the ratio is 1920 ÷ 120 : 1080 ÷ 120 = 16:9. The decimal ratio is 1920 ÷ 1080 = 1.778:1.
Decimal ratios are first scaled to whole numbers, so 1.85:1 becomes 185:100 and then 37:20.
| Ratio | Decimal | Typical use |
|---|---|---|
| 4:3 | 1.333 | Older TVs, many tablets |
| 3:2 | 1.5 | 35 mm photos, some laptops |
| 16:10 | 1.6 | Widescreen monitors |
| 16:9 | 1.778 | HD and 4K video, TVs |
| 64:27 | 2.370 | 2560 × 1080 ultrawide (sold as 21:9) |
| 2.39:1 | 2.39 | Cinema scope |
Resizing without distortion
Keep the ratio by scaling the other side in proportion: height = new width × ratio height ÷ ratio width. At 16:9 a width of 1280 gives 1280 × 9 ÷ 16 = 720 pixels.
Scaling by a percentage multiplies both sides: 50% of 1920 × 1080 is 960 × 540. The pixel count scales by the square of the factor, so half the size has a quarter of the pixels.
About names
A ratio is named only when it is within 2% of a common standard, and approximate matches are marked with ≈. Monitors sold as 21:9 are really 64:27 (2560 × 1080) or 43:18 (3440 × 1440).