Pick a size three ways
Choose an image, then choose how to set the new size. Width and height lets you type exact pixels. Keep proportions is on by default, so changing one side moves the other and the picture does not stretch. Turn it off only when you want a different shape. Percent scales both sides together, so 50 turns a 1200 × 800 image into 600 × 400. Longest edge is handy for websites and email: set it to 1080 and the longer side becomes 1080 pixels while the other side follows.
The result updates as you type. It shows the new dimensions, the file size, and the original beside the resized copy, with a download button.
Check the file, not just the size
Pixel size and file size are different. A smaller image usually makes a smaller file, but format matters too. JPEG and WebP are best for photos and have a quality setting. PNG keeps every pixel exactly, so it can be larger, and it has no quality setting. JPEG fills transparent areas with white.
Related tools
To keep the same dimensions and shrink only the file, use the Image compressor. To cut out part of a picture first, use Crop image. To turn or flip it, use Rotate and flip image.