Last updated: 2026-06-28

Aspect Ratio

An aspect ratio expresses the proportional relationship between a frame's width and its height, written as two integers separated by a colon — for example, 16:9 or 4:3. It describes shape without specifying size, so a 1920 × 1080 pixel screen and a 3840 × 2160 pixel screen share the same 16:9 aspect ratio.

How the calculation works

The formula is straightforward:

$\text{height} = \text{width} \times \frac{r_h}{r_w}$

where $r_w$ is the ratio width and $r_h$ is the ratio height. To solve for width from a known height, invert the fraction:

$\text{width} = \text{height} \times \frac{r_w}{r_h}$

Worked example. A 2560-pixel-wide frame at 21:9:

The result is rounded to the nearest integer because pixels are discrete units.

Simplifying a ratio

Any ratio can be reduced to its lowest terms by dividing both components by their greatest common divisor (GCD). For 1920:1080, the GCD is 120:

$\frac{1920}{120} : \frac{1080}{120} = 16:9$

Simplified ratios help identify the underlying proportional relationship when raw pixel counts make it less obvious — for example, 2560:1440 and 3840:2160 both reduce to 16:9.

Common aspect ratios

Letterboxing and pillarboxing

When content with one aspect ratio is displayed on a screen with a different ratio, the player adds bars to preserve proportions:

• Letterboxing — horizontal black bars above and below, used when the content is wider than the display (e.g., a 21:9 film on a 16:9 screen).
• Pillarboxing — vertical black bars on the sides, used when the content is narrower (e.g., a 4:3 broadcast on a 16:9 television).

Knowing the source and target aspect ratios lets you calculate how much screen area the bars will occupy before deciding whether to crop, scale, or reformat the content.

Photography and sensor formats

Camera sensors add a third common family of ratios. Most DSLR and mirrorless cameras use a 3:2 sensor inherited from 35 mm film, while Micro Four Thirds cameras use 4:3. Smartphone cameras typically shoot at 4:3 but often display a 16:9 crop in the viewfinder. When composing a shot, the aspect ratio of the final output medium — print, web, or social platform — determines how much the image may need to be cropped from the sensor's native frame.