Resize Image in MM Online
Set the exact width and height of an image in millimetres at 300 DPI, with an optional max file size in KB. Free, and your image never leaves your device.
Resize by Millimeters (MM)
Drag and drop your images here
or click to browse your files
Supports JPG, PNG, WebP, and GIF (100% browser-based)
px = mm ÷ 25.4 × DPI. At 300 DPI, 1 mm = 11.81 pixels, so a 35 × 45 mm photo is 413 × 531 px.
To resize an image in mm, upload it above, type the width and height in millimetres and click Resize Image. The file is saved at 300 DPI, so it prints at the size you typed.
By the ImageMagicTool Team · Last updated · Sources
How to resize an image in mm
Upload your image, type the width and height in millimetres and click Resize Image. The unit is already set to mm on this page.
- Upload your image. Click the upload area or drag and drop a JPG, PNG, WebP or GIF file. You can add several images at once.
- Enter the width and height in mm. With the aspect-ratio lock on, typing the width fills in the height so the photo isn't stretched. Turn the lock off to set both numbers yourself, for example exactly 35 × 45 mm.
- Check the pixel size. Under the two boxes the tool shows the output pixel size at 300 DPI, such as 413 × 531 px.
- Click Resize Image, then Download. The download button shows the final file size in KB.
Common photo and paper sizes in mm (with pixels at 300 and 600 DPI)
A passport photo is 35 × 45 mm in the UK and many other countries (413 × 531 px at 300 DPI), a standard ID card is 85.6 × 53.98 mm (1011 × 638 px) and A4 paper is 210 × 297 mm (2480 × 3508 px).
| Photo or paper | Size in mm (W × H) | Pixels at 300 DPI | Pixels at 600 DPI | Source |
|---|---|---|---|---|
| Passport photo (UK and many other countries) | 35 × 45 mm | 413 × 531 px | 827 × 1063 px | GOV.UK passport photo rules |
| US passport photo (2 × 2 in) | 50.8 × 50.8 mm | 600 × 600 px | 1200 × 1200 px | U.S. Department of State photo requirements |
| ID card, bank card (ID-1 / CR80) | 85.6 × 53.98 mm | 1011 × 638 px | 2022 × 1275 px | ISO/IEC 7810 (ID-1) |
| 4 × 6 inch photo print | 101.6 × 152.4 mm | 1200 × 1800 px | 2400 × 3600 px | 4 × 6 in × 25.4 mm per inch |
| A5 paper | 148 × 210 mm | 1748 × 2480 px | 3496 × 4961 px | ISO 216 |
| A4 paper | 210 × 297 mm | 2480 × 3508 px | 4961 × 7016 px | ISO 216 |
| A3 paper | 297 × 420 mm | 3508 × 4961 px | 7016 × 9921 px | ISO 216 |
Photo rules differ by country and change over time, so check the current requirements of the office you are applying to before you print. The metric “10 × 15 cm” photo print (100 × 150 mm, 1181 × 1772 px at 300 DPI) is slightly smaller than a true 4 × 6 inch print (101.6 × 152.4 mm).
Ready-made tools for these sizes: 35 × 45 mm passport photo maker, 2 × 2 inch photo, convert an image to ID card size and resize an image to A4 (210 × 297 mm). For every card format, see the ID card size chart.
MM to pixels at 72, 96, 150, 300 and 600 DPI
To convert mm to pixels, divide by 25.4 and multiply by the DPI. One millimetre is 2.83 px at 72 DPI, 3.78 px at 96 DPI, 5.91 px at 150 DPI, 11.81 px at 300 DPI and 23.62 px at 600 DPI.
| Millimetres | 72 DPI | 96 DPI | 150 DPI | 300 DPI | 600 DPI |
|---|---|---|---|---|---|
| 10 mm | 28 px | 38 px | 59 px | 118 px | 236 px |
| 20 mm | 57 px | 76 px | 118 px | 236 px | 472 px |
| 25.4 mm | 72 px | 96 px | 150 px | 300 px | 600 px |
| 35 mm | 99 px | 132 px | 207 px | 413 px | 827 px |
| 45 mm | 128 px | 170 px | 266 px | 531 px | 1063 px |
| 50 mm | 142 px | 189 px | 295 px | 591 px | 1181 px |
| 85.6 mm | 243 px | 324 px | 506 px | 1011 px | 2022 px |
| 100 mm | 283 px | 378 px | 591 px | 1181 px | 2362 px |
| 210 mm | 595 px | 794 px | 1240 px | 2480 px | 4961 px |
| 297 mm | 842 px | 1123 px | 1754 px | 3508 px | 7016 px |
Pixels are rounded to the nearest whole number. This tool always works at 300 DPI, the usual resolution for photo and document printing. If you need a different DPI, take the pixel size from the table and resize the image in pixels.
MM vs cm vs inches
1 cm = 10 mm and 1 inch = 25.4 mm. Millimetres, centimetres and inches all describe the same printed size, so pick whichever unit your form or printer uses.
| Millimetres | Centimetres | Inches |
|---|---|---|
| 35 × 45 mm | 3.5 × 4.5 cm | 1.38 × 1.77 in |
| 50.8 × 50.8 mm | 5.08 × 5.08 cm | 2 × 2 in |
| 85.6 × 53.98 mm | 8.56 × 5.4 cm | 3.37 × 2.125 in |
| 101.6 × 152.4 mm | 10.16 × 15.24 cm | 4 × 6 in |
| 210 × 297 mm | 21 × 29.7 cm | 8.27 × 11.69 in |
Millimetres are the usual unit on official photo specifications and paper standards, because they avoid decimals: 35 × 45 mm is easier to read than 3.5 × 4.5 cm or 1.38 × 1.77 in. You can switch the unit in the tool at any time, and it keeps the same size. If your size is written in centimetres, use resize image in cm.
Resize an image in mm and KB
Enter the size in mm, then pick a limit under Max file size (KB): 20, 50, 100 or 200 KB, or type your own. The size in mm stays exact, and only the JPG quality is lowered until the file fits.
- The result is a JPG at 300 DPI. PNG, WebP and GIF files are saved as JPG with a white background when a KB limit is set.
- If the limit is too small for that size, the tool tells you the smallest file it can make. It never shrinks your width and height to reach the limit.
- File-size limits are different for every form, so check the limit on your own application before you choose one. To shrink a file without setting dimensions, use the image compressor.
How to print at the exact size in mm
Print at 100% scale (“Actual size”), not “Fit to page”. The resized file carries 300 DPI metadata, so at 100% a 413 × 531 px image prints 35 × 45 mm.
- In the print dialog, choose Actual size or set Scale to 100%, and turn off any “fit” or “shrink” option.
- Measure the first print with a ruler before you print a whole sheet.
- Photo apps and chat apps often remove DPI metadata or rescale images. Print the downloaded file itself, not a forwarded copy.
Frequently Asked Questions
How many pixels is 1 mm?
1 mm is 11.81 pixels at 300 DPI. The formula is px = mm ÷ 25.4 × DPI, so 1 mm is also 23.62 px at 600 DPI, 5.91 px at 150 DPI and 3.78 px at 96 DPI.
How do I resize an image in mm?
Upload the image, keep the unit on mm, type the width and height in millimetres and click Resize Image. The tool converts the size to pixels at 300 DPI (35 × 45 mm becomes 413 × 531 px) and saves the file with 300 DPI metadata.
What is 35 × 45 mm in pixels?
35 × 45 mm is 413 × 531 pixels at 300 DPI and 827 × 1063 pixels at 600 DPI. It is the same size as 3.5 × 4.5 cm.
Is 35 × 45 mm the same as 3.5 × 4.5 cm?
Yes. 10 mm is 1 cm, so 35 × 45 mm and 3.5 × 4.5 cm are the same photo size. In inches it is about 1.38 × 1.77 in.
What is 2 × 2 inches in mm?
2 × 2 inches is 50.8 × 50.8 mm, because 1 inch is exactly 25.4 mm. It is often rounded to 51 × 51 mm. At 300 DPI that is 600 × 600 pixels.
Can I resize an image in mm and set the size in KB?
Yes. Enter the width and height in mm, then choose 20, 50, 100 or 200 KB (or a custom value) under Max file size (KB). The size in mm stays exact and only the JPG quality is lowered to fit the limit.
Why does my print not measure the right size in mm?
Most often the printer dialog is set to Fit to page, which rescales the image. Choose Actual size or 100% scale, then check the print with a ruler.
Is my image uploaded to a server?
No. The image is resized inside your browser on your own device. It is never sent to or stored on our servers.
Is this mm image resizer free?
Yes. There is no charge, no account and no watermark on the downloaded image.
Sources and how we calculate these numbers
Pixel sizes are calculated as mm ÷ 25.4 × DPI and rounded to the nearest pixel. It is the same calculation the tool runs when you type a size, so the tables and the tool always agree. One inch is exactly 25.4 mm by international definition.
- GOV.UK, “Get a passport photo”: printed photos must be 45 mm high by 35 mm wide.
- U.S. Department of State, passport photos: 2 × 2 inches (51 × 51 mm).
- ISO/IEC 7810:2019, identification cards: ID-1 format, 85.60 × 53.98 mm.
- ISO 216, paper sizes: A3 297 × 420 mm, A4 210 × 297 mm, A5 148 × 210 mm.
Written and maintained by the ImageMagicTool Team, who build the resize, ID card and passport photo tools on this site. Found a mistake? Email contact@imagemagictool.com.