How do I calculate an aspect ratio?

Divide the width and the height by their greatest common divisor. 1920 and 1080 share 120, which leaves 16 and 9.

What is the aspect ratio of 1920 × 1080?

16:9, the standard for HD video and most screens. 1280 × 720, 2560 × 1440 and 3840 × 2160 are 16:9 too.

What size is a 4:5 image?

1080 × 1350 pixels is the usual size for a portrait post on Instagram. Any size whose width is four fifths of its height has the same shape.

Why does 1366 × 768 not reduce to 16:9?

Because it is not exactly 16:9: it reduces to 683:384, within a quarter of a percent of 16:9. The calculator gives the exact ratio and the common format it comes closest to.

Aspect ratio calculator

Type a width and a height to read their ratio, or pick a format and resize it without distortion.

Simplest ratio
Resize without distortion
Common formats

Width

Height

Common formats

Resize, keeping the shape

New width

New height

Aspect ratio

16:9

1.778 : 1

Matches: 16:9 · exactly
Resized: 1,280 × 720
Aspect ratio: 16:9

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What an aspect ratio is

The ratio of a picture’s width to its height, written as two whole numbers that share no divisor. 1920 × 1080 reduces to 16:9; 1080 × 1350 to 4:5. Two sizes with the same ratio have the same shape, so one scales to the other without stretching or cropping.

Ratio = width ÷ gcd : height ÷ gcd1920 × 1080 → greatest common divisor 120 → 16:9

Resizing without distortion

Keep the ratio and change one side: the other follows. To fit a 16:9 video into a column 1280 pixels wide, its height is 1280 × 9 ÷ 16 = 720.

New height = new width × height ÷ widthNew width = new height × width ÷ height

The formats worth knowing

16:9: HD and 4K video, YouTube, most screens.
4:3: older screens, the iPad, many compact cameras.
3:2: 35 mm photography and most interchangeable-lens cameras.
1:1: square posts and profile pictures.
4:5: portrait posts on Instagram, 1080 × 1350.
9:16: vertical video: Stories, Reels, TikTok, Shorts.
21:9: ultrawide monitors and cinema.
1.91:1: link previews on Facebook and LinkedIn, 1200 × 630.

Sizing type rather than pictures? The CSS clamp() calculator makes a size scale with the screen.

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