Aspect ratio calculator

How to use the calculator

1. Type the width and height, or use an image and its size is read for you. The image stays on your device.
2. See the closest standard ratio, the exact ratio, and how far apart they are.
3. Choose what you need next: a new size, a fit inside a limit, a different shape, or a print size.

How to keep the same aspect ratio when resizing

Multiply the original height by the new width, then divide by the original width:

new height = original height × new width ÷ original width

For example, reducing a 3200 × 1800 image to 1024 pixels wide gives 1800 × 1024 ÷ 3200 = 576, so the new size is 1024 × 576. Under New size, type either side or a percentage and the others follow.

Why some sizes aren’t exact

Images only have whole pixels. A 3000 × 2000 image reduced to 1024 wide should be 682.67 high, which has to become 683. The difference is tiny, but the ratio is no longer exact. When this happens, the calculator tells you how far off it is and offers nearby sizes that keep the ratio exact, such as 1023 × 682 or 1026 × 684.

Common aspect ratios

• 1:1 Square posts and profile pictures.
• 4:5 Portrait posts in social feeds.
• 9:16 Stories, short videos and full-screen phone images.
• 4:3 Many phone cameras, tablets and older screens.
• 3:2 Many DSLR and mirrorless cameras, and 4 × 6 in prints.
• 16:10 Many laptop screens.
• 16:9 Most TVs and monitors, and widescreen video.
• 21:9 Ultrawide monitors. Sizes sold as 21:9 often differ slightly, such as 2560 × 1080.
• A4 paper About 1:1.414. All A-series paper sizes share this shape.

Fit a limit or change the shape

If an upload form says “maximum 1200 × 800”, use Fit a limit to get the largest size that stays inside both numbers. Your image is never enlarged.

A different shape needs a crop, because resizing alone would stretch the picture. Change shape shows the largest crop, how much comes off each side, and how much of the image you lose. A 3200 × 2400 image cropped to 4:5 becomes 1920 × 2400.

Check a print size

Print shows how many pixels a print needs at the DPI you choose. A 30 × 20 cm print at 300 DPI needs 3543 × 2362 pixels. As a rough guide, 300 DPI looks sharp up close, and around 150 DPI is fine for something viewed from a little distance, such as a poster.

Can I use centimetres or inches?

Yes. A ratio is the same in any unit, so choose pixels, millimetres, centimetres, metres, inches or feet. For example, 8.5 × 11 inches is exactly 17:22.