Aspect Ratio Calculator

Work out the missing width or height that keeps an image or video at its original aspect ratio, with the ratio simplified.

Type the original size, then whichever new dimension you know. The other one is filled in so nothing gets stretched.

Edit either box — the other follows automatically.

Matching size

—

  • —Simplified ratio
  • —Ratio as a decimal
  • —Common name
  • —Megapixels

How Does It Work?

  1. Enter the original sizeThe width and height of the image, video or screen you are starting from, in pixels. Any units work as long as both use the same one.
  2. Type the new width or the new heightWhichever constraint you have been given. The other box fills in automatically with the value that keeps the shape identical.
  3. Check the ratioThe simplified ratio and its common name confirm you are working with what you thought — 1920 × 1080 is 16:9, and a 4:5 crop is not.

What Is It Used For?

Stretching happens when one dimension is changed and the other is not. Getting the second number right is a single multiplication, but doing it in your head with numbers like 1512 and 2016 invites mistakes, and the consequence — a squashed logo or a distorted face — is obvious to everyone who sees it. This calculator does the multiplication and tells you which standard ratio you are actually working in, which is often the more useful piece of information.

  • Resizing an image to a fixed width without distorting it.
  • Working out the height of an embedded video at a given container width.
  • Checking whether a photo is 3:2 or 4:3 before ordering prints.
  • Preparing artwork for a social platform that demands a specific ratio.
  • Scaling a design mockup up or down while keeping every proportion.

Examples

OriginalNew widthNew heightRatio
1920 × 1080128072016:9
1920 × 108080045016:9
4000 × 3000160012004:3
1080 × 13505406754:5
3000 × 200012008003:2

Frequently Asked Questions

How do I calculate a new height from a new width?

Multiply the new width by the original height, then divide by the original width. For 1920 × 1080 resized to 1280 wide: 1280 × 1080 ÷ 1920 = 720. The calculator does this as you type and rounds to whole pixels.

What does 16:9 actually mean?

It is the width divided by the height, reduced to its simplest whole numbers. 1920 ÷ 1080 simplifies to 16:9 because both divide by 120. Any size with the same ratio — 1280 × 720, 3840 × 2160 — has the identical shape.

Why is my result half a pixel out?

Screens cannot show fractional pixels, so the answer is rounded to the nearest whole number. On unusual ratios that can leave the result a tiny fraction away from perfect; the calculator tells you when that has happened.

Which ratio should I use for social media?

It varies by platform and placement, but 1:1 and 4:5 dominate feed images, 9:16 is the standard for full-screen vertical video, and 16:9 remains the norm for landscape video. Always check the current spec, since these change.

Does this work for print sizes?

Yes — the maths is the same for centimetres or inches as for pixels, as long as both original values use the same unit. Note that common print sizes are not all the same ratio, which is why a 4:3 photo needs cropping to fit a 6 × 4 inch print.

Free. No registration. This tool runs entirely in your browser, so the data you enter stays on your device.

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