Simplify a resolution to its aspect ratio, or scale a known dimension to fit a target ratio.
Calculator verified • Last updated: August 2026
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The simplified ratio describes the shape of the frame, independent of its actual pixel resolution — 1920x1080, 2560x1440, and 3840x2160 are all 16:9.
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Scaling keeps the frame's shape identical to the target ratio while resizing it to fit the one dimension you already know.
An aspect ratio expresses the relationship between a frame's width and height as a simplified pair of integers. Simplifying works by dividing both numbers by their greatest common divisor (GCD) — the largest number that evenly divides both — found with the Euclidean algorithm: repeatedly replace the larger number with the remainder of dividing it by the smaller, until the remainder reaches zero.
$$\text{Ratio} = \frac{W}{\gcd(W, H)} : \frac{H}{\gcd(W, H)}$$
W: width, in pixels.
H: height, in pixels.
gcd(W, H): greatest common divisor of width and height.
A 1920x1080 video frame: the Euclidean algorithm finds gcd(1920, 1080) = 120. Dividing both numbers by 120 gives 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, so the simplified aspect ratio is 16:9 — the standard widescreen ratio used by nearly all modern TVs, monitors, and video formats.
Suppose you need a 16:9 banner and already know it should be 1920 pixels wide. The height is found by multiplying the known width by the ratio of height to width: 1920 times (9 divided by 16) equals 1080 pixels — so the full frame is 1920x1080, matching the target ratio exactly.
16:9 — standard widescreen video and displays (1920x1080, 3840x2160).
4:3 — older television and computer monitors, some classic photo formats (1024x768).
21:9 — ultrawide monitors and cinematic widescreen film.
1:1 — square format, common for social media profile images and grid posts.
9:16 — vertical video, the mobile-first format used by short-form video apps.
Stretching or squashing an image to fit a new ratio without preserving the original proportions distorts everything in the frame — circles become ovals, faces look warped. The correct approach is either cropping to the new ratio or scaling both dimensions together by the same factor, never scaling width and height independently by different amounts.
Rounding a scaled dimension too aggressively (e.g. to the nearest 10) before feeding it into video encoding software can also cause errors, since many codecs require even-numbered width and height values — round to the nearest even number rather than an arbitrary one when the result feeds into video export settings.
Aspect Ratio — the proportional relationship between a frame's width and height, expressed as a simplified ratio like 16:9.
GCD (Greatest Common Divisor) — the largest integer that divides two numbers evenly, used to reduce a resolution to its simplest ratio form.
Letterboxing / Pillarboxing — black bars added above/below (letterbox) or beside (pillarbox) content when its aspect ratio doesn't match the display or frame it's shown in.
Divide both the width and height by their greatest common divisor (GCD). For example, 1920x1080 has a GCD of 120, so dividing both by 120 gives 16:9 — the simplified aspect ratio.
Multiply the known dimension by the ratio of the target's other side to its matching side. For example, to find the height of a 1920px-wide image at 16:9, calculate 1920 x (9 / 16) = 1080.
16:9 is a wider, more rectangular ratio common in modern TVs, monitors, and video (1920x1080, 3840x2160). 4:3 is a nearly-square ratio common in older TVs and some photo formats (1024x768, 640x480). The same diagonal size looks visibly different in area and shape between the two.