Resize an image in millimetres
Passport rules, ID card templates and print specifications give sizes in millimetres. Enter the width and height in mm and the DPI, and get an image with exactly the right number of pixels.
- Runs in your browser
- Nothing is uploaded
- No sign-up
- Batch up to 20 images
Drag & drop your image here
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JPG · PNG · WebP · GIF · BMP · AVIF · SVG · up to 50 MB each · up to 20 files
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Processed image will appear here.
How to use the millimetre image resizer
Type the width and height in millimetres, choose the DPI and add your image. It is resized to the pixel size that pair works out to, such as 413 × 531 pixels for 35 × 45 mm at 300 DPI, and cropped from the centre if the shape differs.
- Add your imageIts present size in millimetres at 300 DPI is filled in for you.
- Enter the size in mmType the numbers from your specification, or tap a ready-made size such as 35 × 45.
- Set the DPI and downloadThe file name carries the size and the DPI, so you can tell copies apart.
About this tool
Official photo sizes are nearly always written in millimetres: 35 × 45 mm for most passports, 25 × 35 mm for many ID cards, 50 × 70 mm for a Canadian passport. Print shops use millimetres too, for cards, labels and page sizes. None of those numbers tells you how many pixels the file needs until a resolution is fixed.
Here the millimetres are converted with the DPI you choose, the image is resized to that pixel size, and the DPI is saved in the file. Sizes can be entered to a tenth of a millimetre. When the shape you ask for differs from the photo's own shape, the picture is cropped from the centre to fill it, unless you choose to fit it inside or stretch it instead.
What you get
- Width and height in millimetres, to one decimal place
- Ready-made passport, ID card, bank-card and A4 sizes
- Any resolution from 1 to 2400 DPI
- JPG or PNG output with the DPI saved in the file
- Batch up to 20 images and download a ZIP
When to use the millimetre image resizer
Passport photos specified in millimetres
35 × 45 mm is the passport photo size in most countries. Check the current official rules for head size and background as well.
ID cards and staff badges
Card printers and badge templates give the photo window in millimetres, often 25 × 35 mm.
Business cards and labels
An 85 × 55 mm card or a product label has to arrive at the print shop at the stated size and resolution.
Scanned drawings in a report
When a scanned drawing must sit at a known scale on the page, setting its width in millimetres and its DPI fixes that scale.
Common sizes in millimetres and their pixels
| Size | Used for | Pixels at 300 DPI | Pixels at 600 DPI |
|---|---|---|---|
| 25 × 35 mm | ID card photo | 295 × 413 | 591 × 827 |
| 35 × 45 mm | Passport photo | 413 × 531 | 827 × 1063 |
| 50 × 70 mm | Canadian passport photo | 591 × 827 | 1181 × 1654 |
| 85.6 × 54 mm | Bank-card size | 1011 × 638 | 2022 × 1276 |
| 85 × 55 mm | Business card | 1004 × 650 | 2008 × 1299 |
| 210 × 297 mm | A4 page | 2480 × 3508 | 4961 × 7016 |
How it works
A millimetre is 1/25.4 of an inch, so pixels = millimetres ÷ 25.4 × DPI. At 300 DPI that is 11.81 pixels for each millimetre, and at 600 DPI it is 23.62. Because a pixel cannot be split, each side is rounded to a whole number: 35 mm at 300 DPI is 413.39 pixels on paper and 413 in the file. The largest error that rounding can cause is half a pixel, about 0.04 mm at 300 DPI.
When the width and height you ask for have a different shape from the image, the default is to scale the picture until it covers the whole area and trim the overflow equally from both sides. Nothing is stretched. The finished file is then given the resolution you chose: a density value in the JFIF header for a JPG, and a pixels-per-metre value in the pHYs chunk for a PNG, which is how each format records print size.
Common problems and how to fix them
- The head is cut off or off-centre
- The crop is taken from the middle of the picture. For a portrait where the face is not central, crop it first with the Image Cropper or the Passport Photo Cropper, then set the size here.
- The pixel size is one pixel different from the specification
- Specifications round in different directions. 35 mm at 300 DPI is 413.39 pixels, which some documents round up to 414. If an exact pixel size is required, enter it in the Image Resizer instead.
- The print shop says the resolution is too low
- They are looking at the DPI saved in the file or at the pixel count. Choose 300 DPI here. If the result panel reports that the picture was enlarged, the original does not have enough pixels and a better source is needed.
- My file is too large to upload afterwards
- Print-resolution images are big. Lower the quality slider, or pass the result through the Image File Size Reducer with the form's limit.
Frequently asked questions
How many pixels is a 35 × 45 mm photo?
413 × 531 pixels at 300 DPI, 276 × 354 at 200 DPI and 827 × 1063 at 600 DPI. The formula is pixels = millimetres ÷ 25.4 × DPI.
How do I convert mm to pixels?
Divide by 25.4 to get inches, then multiply by the DPI. At 300 DPI one millimetre is about 11.8 pixels, so 10 mm is 118 pixels and 100 mm is 1181. This page does the sum for you and resizes the image in the same step.
Can I enter a size like 85.6 × 54 mm?
Yes. Sizes are accepted to a tenth of a millimetre. The result is rounded to whole pixels, which at 300 DPI is accurate to within 0.05 mm.
Is this the same as the Passport Photo Cropper?
No. This page crops from the centre of the picture to the size you type. The Passport Photo Cropper lets you drag the crop box over the face first, which is what you want for an ID photo. Use this page when the framing is already right or the image is not a portrait.
What DPI should a passport photo be?
Authorities that accept digital photos usually state a pixel size and not a DPI. Where a DPI is given, 300 is the usual figure. Follow the current official rules for your country.
Can I resize several images to the same size in mm?
Yes. Add up to 20 images, set the size once and press "Process all images". Each one is resized and cropped to the same millimetre size, and the set downloads as a ZIP.
Does the tool change the format of my image?
Not unless you ask it to. A JPG stays a JPG and a PNG stays a PNG. Other formats, such as WebP, are saved as JPG, because WebP cannot record the DPI that a physical size depends on.