Get the right dimensions for 16:9, 4:3, and other ratios

The job

A platform specifies an aspect ratio and you need real pixels: a YouTube thumbnail at 16:9, a product image at 1:1, a banner at 21:9. Given one side, the calculator returns the other.

Worked example: thumbnail

You want a 16:9 thumbnail 1280 wide. Pick 16:9, enter width 1280 — the result is 720 px tall. Or going the other way: height 1080 in, width 1920 out. The second mode runs the reverse question — “what ratio is 3456 × 2160?” → 8:5.

• Custom ratios accept 16:9, 16x9, or 16/9, including decimals like 1.91:1.
• Non-exact divisions round to the nearest pixel: 16:9 at width 1000 gives 563 px, not 562.5.

Then resize or crop

Once you have the target, resize the image to it (Image resizer) or crop the excess off (Image cropper). Resizing to a different ratio stretches the picture — crop first if the subject must stay undistorted.

Limits

The calculator works in whole pixels and accepts values up to 1,000,000. It answers the geometry only — which pixels to keep is a crop decision it does not make.