Resize images online - pixels, percent and ready-made sizes

Aspect ratio is width divided by height - most cameras shoot 3:2, phones 4:3. With “Keep aspect ratio” on, the missing dimension is calculated as:

new height = new width × (original height ÷ original width)

Example: a 4000×3000 px photo resized to 1920 px wide becomes 1920 × (3000 ÷ 4000) = 1440 px tall. If you enter both width and height (say 1000×1000), the image fits inside that box: 1000×750 px. Turn the option off and the picture is stretched to the exact numbers, which distorts it.

Platforms change their recommendations from time to time, so double-check before a paid campaign.

Presets have a fixed shape, so you decide what happens when the photo has a different ratio:

• Crop fills the whole frame and trims the edges evenly. A 4000×3000 photo turned into 1080×1080 keeps the central 3000×3000 area.
• Fit with background shows the whole photo: the same image becomes 1080×810 with 135 px bars of your chosen color above and below.
• Stretch hits the exact size but distorts proportions - rarely a good idea.

For print, what matters is pixels per inch: pixels = inches × DPI. A4 (8.27×11.69 in) at 300 DPI is 2480×3508 px; a 4×6 in photo print needs 1200×1800 px. Posters viewed from a distance look fine at 150 DPI.

JPG and WebP output uses a quality of 85% by default (adjustable from 10 to 100%). “Do not enlarge smaller images” is on by default, because upscaling only adds blur. If you need a smaller file rather than smaller dimensions, try the image compressor.