Work out the size you need first
Resizing works best when you know the destination. A form may state a maximum of 600 pixels wide, a website layout may have a fixed slot, and a print job may need a specific pixel count. Write that number down before you open the tool.
If no size is specified, decide how large the image will actually be displayed. A photo shown in a narrow column does not need camera-resolution pixels, and carrying the full size only makes the file heavier for no visible benefit.
Resize by pixels or by percent
Pixel mode sets the output exactly: enter a width and height and the image is resampled to those numbers. Percent mode scales the current size, so entering 50 percent halves each side and leaves you with a quarter of the original pixels.
The aspect ratio lock keeps the shape of the picture. With the lock on, entering one dimension calculates the other, which is what stops faces and circles from stretching. Turn it off only when a form demands an exact non-matching shape.
- Pixels for an exact target such as 1200 by 630
- Percent for a quick reduction such as 50 percent
- Aspect lock on to keep proportions and avoid distortion
- JPG output for photos, PNG output for transparency
Choose the output format
The tool writes a JPG or a PNG file. JPG suits photographs and keeps the result small, while PNG holds a transparent background instead of filling it with white.
Resizing does not convert the file into something it was not. A JPG stays a JPG unless you choose PNG output, and neither format restores detail that a previous edit already threw away.
Check the numbers on the result
Check the new dimensions after you generate, because a single wrong digit is the difference between a 1200 pixel image and a 120 pixel one. Download only once the numbers match the target you set.
Inputs are accepted up to 25 MB, 16,000 pixels per side, and 48 megapixels. Oversized files are rejected with a message that shows the current width and height, so you can see exactly which limit was hit.
Resize when you want fewer bytes, compress when you want a limit
Fewer pixels almost always means a smaller file, which is why resizing is the first move when an image is too heavy. It is not a guarantee of a specific size, because detail and format still decide how many bytes each pixel costs.
When a form names a hard limit such as 200 KB, follow resizing with compression. The compressor takes the resized image and works toward a maximum you choose, then reports the final size so you can verify it.