Aspect Ratio Calculator

What to work out

Width, pixels

Height, pixels

Result

Aspect ratio16:9
Size1920 × 1080
Nearest standard16:9 (off by 0%)
As a decimal1.7778
Megapixels2.07
Orientationlandscape

Greatest common divisor and nothing harder

Reduces a pixel size to its aspect ratio, finds the nearest standard proportion, and works out the second side when the ratio is fixed in advance.

An aspect ratio is width over height reduced to the smallest whole numbers. 1920 and 1080 both divide by 120 and become the familiar 16:9; 2560 by 1080 gives 64:27, which is marketed as '21:9' even though no true 21:9 exists.

The reverse job comes up more often: the ratio is known, one side is known, and the other has to follow. It is one multiplication, but it is easy to get wrong and the result shows immediately — a stretched image or black bars down the sides.

What this calculator shows

The reduced aspect ratio and its decimal value
The nearest standard proportion and how far off it is
The second side, given a ratio and one dimension

What to keep in mind

The ratio comes from the greatest common divisor, so unusual sizes produce unfamiliar fractions like 683:384.
The nearest standard is matched on the decimal value: a small deviation usually means rounding during a crop.

FAQs

How do I find an image's aspect ratio?

Divide width and height by their greatest common divisor. For 1920 and 1080 that is 120, which gives 16:9.

Which ratios count as standard?

16:9 for video and monitors, 4:3 on older screens and some cameras, 3:2 on interchangeable-lens cameras, 1:1 and 4:5 on social, and 9:16 for vertical video.

What is 21:9?

A marketing name for ultrawide screens. The real proportion is usually 64:27 at 2560 × 1080 or 43:18 at 3440 × 1440 — nothing on sale is exactly 21:9.

Why do black bars appear?

Because the material's ratio does not match the screen's. The player fits the whole frame in and pads the rest rather than stretching the picture.

Worked example

Ordinary Full HD

Input: 1920 × 1080 pixels

Output: 16:9, nearest standard 16:9

Note: Both numbers divide cleanly by 120, so the fraction comes out tidy. For 2560 × 1080 the common divisor is only 40 and the ratio lands on 64:27 — the one sold as 21:9.

Useful links

All tools in Photo & Video

Aspect Ratio Calculator

Result

Related tools

Image Resize Calculator

Screen PPI Calculator

DPI and Print Size Calculator

Useful links