How the image resizer works
This tool uses the Canvas API to redraw your image at the exact dimensions you specify. The browser's built-in interpolation handles the scaling, producing smooth results for both upscaling and downscaling operations.
When you enter dimensions in millimeters, the tool converts them to pixels using the DPI (dots per inch) you select. For example, a 50mm × 50mm image at 300 DPI becomes 591 × 591 pixels. This is useful for preparing images for print, ID photos, or documents with specific physical size requirements. The pixel equivalent is shown live beneath the inputs so there's no guesswork.
Output format options
- JPEG — Best for photographs. Smallest file size with adjustable quality. No transparency.
- PNG — Lossless quality, supports transparency. Larger files.
- WebP — Modern format with excellent compression. Not supported by all older software.
Aspect ratio locking
By default, the aspect ratio is locked. When you change the width, the height adjusts proportionally to prevent distortion. Toggle the lock off if you need to set non-proportional dimensions (for example, cropping a landscape photo into a square).
Size limits
Browsers cap how large a canvas can be — mobile Safari is the tightest at roughly 16.7 megapixels. Beyond that limit a canvas silently produces a blank image rather than raising an error, so the tool checks your target dimensions up front and explains the problem instead of handing you an empty file.
Everything runs locally in your browser. The image is drawn to a canvas in memory, re-encoded in your chosen format, and offered as a download. No data is transmitted to any server.