To make an image file smaller, should I resize it or compress it?

The difference in two lines

• Resizing: a 1600 pixel wide image becomes 1000 wide. The pixel count drops from 1,920,000 to 750,000, under 40% of what it was. Every pixel removed is one that never needs storing.
• Compressing: the image stays 1600×1200, but the encoder stores its detail less precisely, so the bytes shrink while the pixel count stays put.

The comparison, measured

Combining the two produced a file under a third of the compress-only result. But that is only worth it if the photo really will be shown at 1000 pixels wide or less. If it will be shown at 1600, shrinking it makes it blurry on screen, and compression alone is the right call.

How to decide

1. Find out the width the image will be shown at: on a product page, in a card, in a message. Your platform's guidance usually says.
2. If your photo is much wider than that, start with the Image resizer and reduce the width, saving the output as PNG so nothing is lost before compression.
3. Put the result into the Image compressor and pick a quality; the tool shows the size before and after.
4. If the dimensions are already right, skip the resizing step and compress directly.

A note on order

Why resize first and compress second, not the other way round? Compression adds small artifacts. Compress first and then resize, and the smaller image carries those artifacts and then needs a fresh encode when saved. Resize and save in a lossless format, then compress once, and the image goes through only one lossy step. The resizer also has its own quality slider, so if you already know the quality you want, you can save at it straight from there.