How resizing works
The resizer reads the picture's natural width and height, lets you type new values, and redraws the image onto a new canvas of exactly those dimensions using the browser's built-in scaler. With the lock checked, editing the width sets the height to width divided by the original aspect ratio (rounded to a whole pixel), and editing the height sets the width the same way. Unlock it to enter both values independently, which stretches or squashes the picture. The output is named after your file, like photo-1200x900.jpg.
Worked example
A 4000×3000 photo has an aspect ratio of 4:3. Typing a width of 1200 gives a height of 900. A 4032×3024 iPhone photo reduced to a width of 1080 gives 810. A 1600×900 widescreen image typed as height 450 gives width 800. The memory the browser needs is also lower after resizing: 4000×3000 is 12 million pixels, about 48 MB uncompressed in RGBA, while 1200×900 is 1.08 million pixels, around 4.3 MB.
Which format comes out
| Input type | Output | Notes |
|---|---|---|
| JPG | JPG at 92% quality | Fixed value, no slider |
| WebP | WebP at 92% quality | Alpha kept |
| PNG, GIF, AVIF, SVG or any other | PNG by default | GIF, AVIF and SVG cannot be written back, so a note under the format menu says so. Pick PNG, JPG or WebP. A GIF is resized as its first frame only. |
JPG, PNG and WebP input default to the same format; you can change it with the Output format menu, so a large PNG photo can be resized straight to JPG or WebP. JPG output has a white fill under any transparent area, and lossy output uses a fixed 92% quality. For a precise file-size target, follow up with the compressor.
Limits and common mistakes
- Very large reductions. The tool uses the browser's high-quality smoothing and, for big reductions, scales down in halving steps (for example 4000 to 2000 to 1000 to 500) instead of one jump, which keeps thin lines and text clean. Very fine detail can still soften at extreme ratios.
- Enlarging. Making a 400 px image 1600 px wide gives a softer picture, not new detail.
- Unlocking the ratio by accident. Typing both values with the lock off distorts the picture. The original size is shown above the fields so you can check the proportion.
- Exceeding canvas limits. Browsers cap canvas size, commonly around 16,384 pixels per side or about 268 million pixels in total, and mobile browsers are stricter. The tool refuses sizes beyond 16,384 pixels per side or 100 megapixels in total and tells you why, instead of exporting a blank file. Phones may still fail earlier than that.
- Resizing is not compression. Pixel count and file size are related but not the same. For a precise file-size target use the Image Compressor.
For circular or square avatars, Crop Image is the right companion.