Aspect Ratio Calculator

Calculate the aspect ratio of any width and height. Enter a target width to get the scaled height — perfect for video, images, and screen design.

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Enter your values and click Calculate

The aspect ratio of an image, video, or screen is the proportional relationship between its width and height, expressed as two numbers separated by a colon (for example, 16:9 or 4:3). This ratio stays constant when you scale the content up or down, which is why it matters so much for responsive design, video production, and print layouts. A 1920×1080 video and a 1280×720 video both have a 16:9 aspect ratio — the proportion is identical even though the pixel counts differ. This calculator takes any width and height, reduces the ratio to its simplest whole-number form using the greatest common divisor, and optionally computes the correct height for a given target width. Use it when resizing images to avoid distortion, when setting up video exports at a non-native resolution, when designing responsive UI components, or when checking whether an existing asset matches a required aspect ratio.

How It Works

The aspect ratio is calculated by dividing both the width and height by their greatest common divisor (GCD) — the largest integer that divides both numbers evenly. For example, 1920 and 1080 share a GCD of 120, so 1920 ÷ 120 = 16 and 1080 ÷ 120 = 9, yielding the ratio 16:9. The decimal ratio is simply width ÷ height (1920 ÷ 1080 ≈ 1.7778 for 16:9). When a target width is provided, the scaled height is calculated by keeping the ratio constant: target height = target width × (original height ÷ original width). For example, scaling 1920×1080 to a target width of 1280: target height = 1280 × (1080 ÷ 1920) = 1280 × 0.5625 = 720 px. This ensures the scaled image or video fills the frame without distortion.

Examples

Full HD Video
Finding the aspect ratio of a standard 1920×1080 Full HD frame.
Result: 16:9 (decimal ratio 1.7778).
Scale 4K to 1080p
A 3840×2160 (4K) frame scaled to a target width of 1920.
Result: 16:9 — target height at 1920px wide is 1080px.
Portrait Instagram Photo
Checking the ratio of a 1080×1350 portrait post.
Result: 4:5 (decimal ratio 0.8).

Frequently Asked Questions

What does 16:9 mean?
16:9 means the width is 16 units for every 9 units of height. It is the standard aspect ratio for widescreen televisions, YouTube videos, and most modern monitors. At any resolution — 1280×720, 1920×1080, 3840×2160 — the 16:9 ratio holds as long as both dimensions are proportional.
What is the difference between aspect ratio and resolution?
Resolution refers to the total number of pixels (e.g. 1920×1080), while aspect ratio describes only the proportional shape of the frame (e.g. 16:9). Two videos can share the same aspect ratio but have very different resolutions. Resolution affects file size and sharpness; aspect ratio determines the shape of the image.
Why does my scaled height come out slightly off?
Pixel dimensions must be whole numbers, so the calculator rounds the target height to the nearest integer. For most practical uses this rounding is imperceptible. If you need exact pixel-perfect dimensions, choose a target width that divides evenly into the original width, or verify the ratio with the decimal value shown.
What aspect ratio should I use for social media?
Common social media aspect ratios: Instagram square (1:1, e.g. 1080×1080), Instagram portrait (4:5, e.g. 1080×1350), Instagram/YouTube landscape (16:9, e.g. 1920×1080), TikTok/Reels (9:16, e.g. 1080×1920), Twitter/X header (3:1). Always check the current platform guidelines as these specifications change.