Screens talk in pixels. Printers talk in inches or centimeters. Forms sometimes ask for one and give you the other. Moving between them is easy once you know the one number that connects them: pixels per inch.
The key idea
A pixel has no fixed physical size. How big it is depends on how many pixels you pack into each inch, which is the PPI. To convert between units you need to know the PPI, or decide on one. If you want to understand where that figure comes from, read DPI vs PPI first.
The formulas
- Pixels to inches: pixels divided by PPI
- Inches to pixels: inches multiplied by PPI
- Inches to centimeters: inches multiplied by 2.54
- Centimeters to inches: centimeters divided by 2.54
- Centimeters to pixels: centimeters divided by 2.54, then multiplied by PPI
Worked examples
Example 1. You want a 6 x 4 inch print at 300 PPI. Multiply: 6 x 300 = 1800 pixels, 4 x 300 = 1200 pixels. You need an image at least 1800 x 1200.
Example 2. A form asks for a photo 3.5 cm wide and 4.5 cm tall at 300 PPI. First convert to inches: 3.5 / 2.54 is about 1.38, and 4.5 / 2.54 is about 1.77. Then multiply by 300: roughly 413 x 531 pixels.
Example 3. You have a 3000 x 2000 pixel photo and want to know how large it can print well at 300 PPI. Divide: 3000 / 300 = 10 inches and 2000 / 300 = about 6.7 inches. So roughly 10 x 6.7 inches.
Reference table at 300 PPI
| Print size (inches) | Pixels needed |
|---|---|
| 3.5 x 5 | 1050 x 1500 |
| 4 x 6 | 1200 x 1800 |
| 5 x 7 | 1500 x 2100 |
| 8 x 10 | 2400 x 3000 |
| 11 x 14 | 3300 x 4200 |
| A4 (8.27 x 11.69) | 2480 x 3508 |
Can you print with fewer pixels?
Yes. 300 PPI is a standard for sharp prints held in the hand. Large prints seen from a distance, such as posters, banners and wall art, look fine at lower PPI, because viewers stand further back. For a closer look at print preparation, read how to resize an image for printing.
What about screens?
For anything shown only on screen, inches and centimeters don’t really matter. Just think in pixels. A website image is as big as its pixel dimensions, regardless of any DPI number saved in the file.
Common mix-ups
- Changing the DPI field doesn’t add detail. It only changes the print size the file claims. See can you increase image resolution.
- Rounding. Round to the nearest whole pixel. A pixel can’t be fractional.
- Assuming 72 or 96 DPI for screens. It’s mostly irrelevant for display today.
For forms and documents
When a portal gives dimensions in centimeters or millimeters, decide on 300 PPI and convert, then resize to the exact pixel result. Passport and ID-style requirements often work this way. Our passport photo size guide shows how this plays out.
Once you’ve worked out your pixel numbers, enter them straight into our free image resizer.