Aspect Ratio Calculator

Compute the aspect ratio of any width × height as a clean fraction (16/9, 4/3, 21/9, …). Enter dimensions or pick a preset.

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What Is Aspect Ratio?

The aspect ratio describes the proportional relationship between the width and height of a rectangle. Enter any width and height to get the ratio as a clean fraction, or pick a preset to see standard dimensions for common screens, cameras, and platforms.

How It Works

R=WHR = \frac{W}{H}

The result is simplified to the lowest-integer fraction using the greatest common divisor, so 1920 × 1080 becomes 16/9 rather than 1920/1080.

Common Aspect Ratios

RatioTypical uses
16:9HD TV, 1080p/4K monitors, YouTube, most laptops
4:3Classic CRT TV, older cameras, iPad
21:9Ultrawide monitors, widescreen cinema
1:1Instagram posts, profile pictures
3:2DSLR and mirrorless photos, 35 mm film
9:16TikTok, Instagram Reels, YouTube Shorts

Practical Uses

Video production — Before exporting, confirm your canvas matches your delivery platform. YouTube and Netflix require 16:9; Instagram Reels and TikTok expect 9:16.

Photo printing — A 4×6 print is 3:2; a 5×7 print is roughly 7:5. Knowing the ratio prevents unexpected cropping when ordering prints from a square camera sensor.

Screen design — UI mockups must match the target device. A phone screen is typically 9:16 or 19.5:9 (modern edge-to-edge); a desktop is usually 16:9.

Projector setup — Check whether a projector is 4:3 or 16:9 before placing the screen, or part of the image will be cut off or letterboxed.

Resizing without distortion — Keep the same ratio when scaling: if the original is 1280 × 720 (16:9), scale to any width W and height W × (9/16).

For related tools, see Ratio & Proportion Calculator (scale any two quantities proportionally) and Gear Ratio Calculator (mechanical drive ratios).

Frequently Asked Questions (FAQ)

What does aspect ratio mean?

Aspect ratio is the ratio of width to height, expressed as two integers separated by a colon or slash (e.g., 16:9 or 16/9). It describes shape, not size — a 1080p screen and a 4K screen both have a 16:9 ratio despite having different pixel counts.

Why does 1920 × 1080 give 16:9 and not some other fraction?

1920 / 120 = 16 and 1080 / 120 = 9, so the GCD is 120 and the simplified ratio is exactly 16/9. Most common resolutions are multiples of simple integer ratios by design.

How do I find the height if I know the width and ratio?

Rearrange the formula: $H = W \div R$. For a 1200 px wide image at 16:9, the ratio $R = 16/9$, so $H = 1200 \div (16/9) = 1200 \times (9/16) = 675$ px.

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