Keep the proportions
Changing only the width or only the height stretches the picture. Keep the aspect ratio locked so the other side changes automatically. Our resize tool does this by default.
Shrink instead of enlarge
Making an image smaller keeps it sharp, because the software throws away pixels. Making it bigger forces the software to invent pixels, which looks blurry. If you need a large image, start from the largest original you have.
Resize first, then compress
If you also need a small file, resize to the pixel size you need first, and then reduce the file size in KB. This gives better quality than compressing a huge image down to a tiny file. See how to reduce image size in KB.
Work from the original
Every time you save a JPG, it loses a little quality. Keep your original file and make each resized version from it.
Pick a sensible format
Use JPG for photos and PNG for graphics or images with transparent areas. If you are unsure, read our JPG vs PNG vs WebP guide.