Resize Image in mm
Enter a width and height in millimetres and a DPI, and the tool works out the pixel size, resizes the picture and shows the result before…
Drag and drop an image here
JPG, PNG, WebP, AVIF, HEIC, GIF or BMP · one file · up to 50 MB
Your image stays on this device and is never uploaded.
How to use the Resize Image in mm
- Choose an image, or drag it onto the drop area. It stays on your device.
- Pick Millimetres, then enter the width and height you need. With Lock aspect ratio on, the second value follows the first so the picture is not squashed.
- Check the DPI. It only decides how many pixels each unit holds, so the same size at a higher DPI gives a bigger, sharper file.
- Choose JPG, PNG or WebP and, for JPG or WebP, the quality. The preview shows the new pixel size before you save.
- Press Resize image, then download the result. The original file is never changed.
About this tool
Millimetres are the unit most photo and ID sizes are written in, for example 35 × 45 mm. To turn that into pixels you need a DPI: pixels = millimetres ÷ 25.4 × DPI. At 300 DPI, 35 × 45 mm is 413 × 531 pixels, at 150 DPI it is 207 × 265 pixels, and at 600 DPI it is 827 × 1063 pixels.
Because the conversion divides by 25.4, small rounding differences are normal: a size that does not land on a whole pixel is rounded to the nearest one. The tool shows the exact pixel width and height it will use, so you can see the rounding instead of guessing.
If your goal is a fixed shape such as 35 × 45 mm from a larger photo, the better route is to crop to that shape first so the face or subject is not stretched. This page is for scaling a whole picture to a size in millimetres.
Practical uses
- Scaling a picture to the millimetre size a template or print shop gives you.
- Checking how many pixels a printed size needs at a given DPI.
- Producing a small image for a label, badge or card layout.
Tips for better results
- Write the size the same way the form does (width first, then height).
- Use 300 DPI if the image will be printed and 96 DPI if it only has to fit a screen.
- Check the pixel size in the preview, not just the millimetres.
Frequently asked questions
How many pixels is 1 mm?
At 300 DPI, 1 mm is about 11.8 pixels. At 150 DPI it is about 5.9 pixels. The value depends on the DPI.
Is a larger DPI always better?
No. A higher DPI gives more pixels and a bigger file. It helps for printing but does nothing for a form that only checks pixel size or KB.
Can I keep the proportions?
Yes. Lock aspect ratio is on by default, so changing one side changes the other to match the picture.
Is my image uploaded?
No. The file is read and rewritten in your browser, and it never leaves your device.
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Privacy
Your image is processed in your browser on your own device. It is not uploaded to Paul Digital or any other server, and nothing is stored once you close the page.