A DPI calculator for pixels, inches, centimetres and print sizes
Whether you are ordering prints, preparing a poster or filling in a form that wants a “300 DPI photo”, the maths is the same: pixels = inches × DPI. This DPI calculator does it in every direction. Turn an image’s pixel size into a print size in inches, centimetres and millimetres; find how many pixels a 4 × 6 in or A4 print needs; or check what DPI your photo reaches at the size you want.
A table of common print sizes — from passport photos to A2 and 24 × 36 in posters — shows the pixels needed at 300 and 150 DPI and, once you enter your image size, the DPI your image would print at for each one. A viewing-distance calculator explains why a billboard looks sharp at 20 DPI. DPI and PPI are used interchangeably here, as most print services do.
How to use the DPI Calculator
- Choose what you want to calculate: “Pixels → print size”, “Print size → pixels”, “Find the DPI” or “Megapixels → print size”.
- With only a megapixel figure, pick “Megapixels → print size”, add the shape (3:2, 4:3…) and an optional crop to get the pixel size and the largest print at 300, 240 and 150 PPI.
- Enter the image width and height in pixels, the print size and unit, or both, depending on the mode.
- Type a DPI or tap 72, 150, 300 or 600. In “Print size → pixels” you can also pick a common size such as 4 × 6 in or A4.
- Read the result and the extra figures: megapixels, sizes at other DPIs and the quality verdict.
- Check the table to see every common print size your image can handle, and set a viewing distance to find the DPI that looks sharp from there.
DPI Calculator features
Three calculators in one
Pixels to physical size, physical size to pixels, and the DPI a given image reaches at a given size.
Inches, cm and mm
Uses the exact definition 1 inch = 25.4 mm, so metric paper sizes such as A4 convert precisely.
Print-size table
Twelve common photo, paper, passport and poster sizes at 300 and 150 DPI, with your image’s DPI for each.
Orientation aware
Your image is rated in portrait and landscape and the better fit is used.
Viewing-distance guide
Finds the minimum DPI that looks sharp from any distance, based on 1 arcminute visual acuity.
DPI formulas with worked examples
Pixel counts are rounded to whole pixels. To set the DPI value stored inside a file without changing its pixels, use the image DPI checker.
- Print size (in) = pixels ÷ DPI. 3000 × 2000 px at 300 DPI prints at 10 × 6.67 in (25.4 × 16.93 cm).
- Pixels = inches × DPI. A 4 × 6 in print at 300 DPI needs 1200 × 1800 px, about 2.16 megapixels.
- Pixels from millimetres = mm ÷ 25.4 × DPI. A4 (210 × 297 mm) at 300 DPI needs 2480 × 3508 px; a 35 × 45 mm passport photo needs 413 × 531 px.
- DPI = pixels ÷ inches. An 1800 × 1200 px photo printed at 12 × 8 in reaches 150 DPI.
Pixels needed for common print sizes
| Print size | At 300 DPI | Megapixels | At 150 DPI |
|---|---|---|---|
| 2 × 2 in (US passport) | 600 × 600 | 0.36 | 300 × 300 |
| 35 × 45 mm (passport) | 413 × 531 | 0.22 | 207 × 266 |
| 4 × 6 in (10 × 15 cm) | 1200 × 1800 | 2.16 | 600 × 900 |
| 5 × 7 in | 1500 × 2100 | 3.15 | 750 × 1050 |
| 8 × 10 in | 2400 × 3000 | 7.2 | 1200 × 1500 |
| A4 (210 × 297 mm) | 2480 × 3508 | 8.7 | 1240 × 1754 |
| A3 (297 × 420 mm) | 3508 × 4961 | 17.4 | 1754 × 2480 |
| 24 × 36 in poster | 7200 × 10800 | 77.76 | 3600 × 5400 |
How much DPI do you really need? Viewing distance matters
People with normal (20/20) vision can separate details about one arcminute apart. From that, the DPI at which individual pixels become invisible is roughly 3438 ÷ viewing distance in inches. At 12 inches (30 cm) about 286 DPI is enough, which is why 300 DPI became the standard for hand-held prints. A poster at 3 feet needs about 95 DPI; a billboard seen from 30 metres gets away with single digits.
| Viewing distance | DPI that looks sharp | Typical use |
|---|---|---|
| 25–30 cm (10–12 in) | 286–344 | Photo prints, books, magazines |
| 60 cm (2 ft) | 143 | Desk calendars, framed photos on a desk |
| 1 m (3 ft) | 87–95 | Posters, wall art |
| 3 m (10 ft) | 29 | Banners, exhibition graphics |
| 15 m (50 ft) | 6 | Billboards |
DPI Calculator FAQ
How many pixels do I need for a 300 DPI print?
Multiply each side in inches by 300. A 4 × 6 in print needs 1200 × 1800 px, an 8 × 10 in print 2400 × 3000 px and A4 2480 × 3508 px. Use “Print size → pixels” in the DPI calculator for any other size.
How do I convert pixels to inches?
Divide the pixels by the DPI: at 300 DPI, 1500 pixels are 5 inches. Multiply inches by 2.54 for centimetres.
What is the difference between DPI and PPI?
PPI (pixels per inch) describes an image or screen; DPI (dots per inch) originally described printer ink dots. In everyday use, and in most print shops and forms, “DPI” means PPI, and this calculator treats them as the same number.
Is 72 DPI bad for printing?
The tag alone means nothing; the pixel count for the print size is what matters. A 3000 × 2000 px photo tagged 72 DPI still prints sharply at 10 × 6.67 in.
What size can I print from a 12, 24 or 48 megapixel camera?
Divide the pixel dimensions by the PPI. A 24 MP 3:2 file (6000 × 4000 px) gives 20 × 13.3 in at 300 PPI, 25 × 16.7 in at 240 and 40 × 26.7 in at 150. These PPI targets are conventions (lab standard, good inkjet, large posters), not rules, so check your lab’s guideline. Cropping to half the width keeps a quarter of the megapixels.
How many megapixels do I need for an A4 print?
About 8.7 megapixels for 300 DPI (2480 × 3508 px). A 12-megapixel phone photo comfortably covers A4, and about 3.9 megapixels (1654 × 2339 px) is enough at 200 DPI.
Why does my print shop accept 150 DPI for posters?
Posters are viewed from a metre or more, where 100–150 DPI already looks sharp (see the viewing-distance table).