How do I resize an image to custom dimensions in cm, mm or inches?
Upload your image, type the width and height, and pick the unit: pixels, cm, mm or inches. For cm, mm and inches, also set the DPI (300 for print, 200 for most forms). The tool will resize image to custom dimensions and shows the exact pixel size it will create, for example "3.5 × 4.5 cm = 413 × 531 pixels at 300 DPI". Choose a fit mode, an optional KB limit, and download.
Why use cm or inches instead of pixels?
Many notices, print shops and ID card makers do not speak in pixels. They say "photo 3.5 cm × 4.5 cm", "signature 6 cm × 2 cm" or "4 × 6 inch print". A screen image has no physical size until you decide how many pixels make one inch. That number is the DPI (dots per inch) or PPI.
The conversion is simple:
- Pixels = inches × DPI
- Pixels = (cm ÷ 2.54) × DPI
- Pixels = (mm ÷ 25.4) × DPI
The tool does this for you and shows the result live under the input boxes, so you never guess.
Which DPI should you choose?
| DPI | When to use | 3.5 × 4.5 cm becomes |
|---|---|---|
| 96 / 100 | Screen-only use, very small file sizes | 138 × 177 px (100 DPI) |
| 150 | Basic printing, office documents | 207 × 266 px |
| 200 | Online forms that also print the photo | 276 × 354 px |
| 300 | Photo-quality printing, ID cards | 413 × 531 px |
| 600 | Professional print, scanning artwork | 827 × 1063 px |
A higher DPI gives more pixels and a sharper print, but also a bigger file. If your form has a KB limit, 200 DPI is often the best balance.
Steps to resize with custom width and height
- 1Upload your image
Photos, scans, screenshots and graphics all work.
- 2Choose the unit and type the size
Select px, cm, mm or in. Enter width first. Tick Lock aspect ratio if you want the height filled in automatically.
- 3Set DPI and fit mode
Use Crop to fill for photos, Fit with padding for documents and logos.
- 4Download
Optionally limit the file size in KB. Then save as JPG, PNG or WebP.
Does the DPI value get saved in the file?
Most online forms only read the pixel width and height, so the pixel count is what matters. Some print software also reads a DPI tag stored inside the file. Browsers do not always write that tag. If a print shop needs a set DPI tag, tell them the intended size, for example "print at 3.5 × 4.5 cm". Because the pixel count is already correct, the print will be sharp. You can read more about pixels per inch.
Common custom sizes
- 3.5 × 4.5 cm: passport-size photo for Indian forms. Ready-made in the Passport Photo Resizer.
- 6 × 2 cm: a common signature box size. Use Resize Signature by Pixels for clean signatures.
- 4 × 6 inch: postcard photo print.
- A4 (21 × 29.7 cm): full-page document image. To make a PDF, use Convert Images to PDF.
Prefer pixels only? Use Resize Image by Pixels.
Frequently Asked Questions
How do I resize an image in cm?
Choose Custom, set the unit to cm, type the width and height, pick a DPI and download. The tool converts cm to pixels for you.
How do I convert cm to pixels?
Pixels = (cm ÷ 2.54) × DPI. For example 3.5 cm at 300 DPI is about 413 pixels.
Which DPI should I use?
Use 300 DPI for printing, 200 DPI for forms that may print the image, and 100 DPI for screen-only use.
Does the DPI value matter for online forms?
Online forms usually check only pixels and KB. DPI matters when you convert physical sizes to pixels or print.
Can I keep the proportions?
Yes. Tick Lock aspect ratio and type only the width.
Is there a size limit?
You can set up to 6000 × 6000 pixels.
About this tool
Built and maintained by the PhotoKB Editorial Team. We test every tool with real phone photos, scans and PDFs before each update. Exam and portal values are based on public official notifications. PhotoKB is not linked to any exam body, so always confirm current rules on the official website. Last updated: 8 November 2026.