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Aspect Ratio Calculator

Use RatioForge as a fast aspect ratio calculator for images, videos, designs and screen sizes. Enter a width and height to simplify the ratio, or choose a ratio such as 16:9, 9:16, 4:5 or 1:1 and calculate the missing dimension.

By the RatioForge team · Last updated July 2026

Calculator

px
px
Ratio
1920 1080 16:9
Drop an image to read its ratio
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Watch how it works

A quick tour of the calculator — pick a ratio, enter one dimension, and copy the exact width or height you need.

Common aspect ratios

Size / ratioLabelUse-case
16:91920×1080YouTube, TVs, monitors, presentations
9:161080×1920TikTok, Reels, Stories, Shorts
4:51080×1350Instagram portrait feed posts
1:11080×1080Square posts, profile pictures, icons
21:92560×1080Ultrawide monitors and cinematic layouts
3:23000×2000Photography, DSLR and mirrorless cameras
4:31024×768Classic screens, slides and older cameras
2.39:12048×858Anamorphic widescreen cinema

Formula

Worked example. For a 1200 px-wide image at 16:9, height = 1200 × 9 ÷ 16 = 675 px. To simplify an existing size, divide both sides by their greatest common divisor: 1920 and 1080 share a GCD of 120, so 1920×1080 reduces to 16:9.

When to use an aspect ratio calculator

The calculator is useful before exporting a YouTube video, cropping an Instagram post, sizing a website image, preparing a presentation slide or checking an existing file. It works with pixels and proportional dimensions, so the same logic applies whether you are planning a 1920×1080 video, a 1080×1350 portrait image or a custom web container.

Aspect ratio describes the shape of a rectangle, not its quality or file size. A small 1280×720 image and a large 3840×2160 video are both 16:9 because they reduce to the same proportion. That is why ratio comes before resolution: choose the shape first, then choose how many pixels you need.

For content work, the wrong ratio usually creates visible problems. A horizontal image may get cropped in a vertical Story, a square logo can look padded inside a widescreen video, and a web hero image may shift awkwardly across breakpoints. Calculating the ratio before exporting avoids stretching, black bars and accidental crops.

Some visitors only need the missing height for a 1200px-wide image; others want to understand why their video has black bars or why two files with different pixel counts can share one ratio. Calculate and copy your result above, then move into a more specific calculator below when you know your destination platform.

Cropping, black bars and stretching

When a file does not match the shape of its destination, you get one of three outcomes. Black bars appear when the player pads a mismatched ratio — pillarboxing (bars left and right) for a wide clip in a tall frame, and letterboxing (bars top and bottom) for an ultrawide clip in a 16:9 player. Cropping trims the edges to fill the frame, which can cut off a subject. Stretching distorts the image to force a fit. The reliable fix is to calculate the target ratio first and export to it, rather than resizing afterwards.

This is the general-purpose calculator. When you already know the destination, the platform-specific calculators below load the right preset and add platform notes — for example the YouTube, TikTok and Instagram calculators.

Frequently asked questions

Popular calculators for specific ratios and platforms:

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