DPI Calculator — How Many Pixels to Print at 300 DPI
To print sharply, your image needs enough pixels for its size. The rule is simple: pixels = (cm ÷ 2.54) × DPI, because 1 inch equals 2.54 cm and DPI means dots (pixels) per inch. At the print standard of 300 DPI, a 10×15 cm photo needs 1181×1772 pixels (about 2.1 MP). Enter your print size and target DPI below and this calculator gives you the exact pixel dimensions and megapixels you need — plus a quick-reference table for the most common sizes.
When to use this calculator
- Check if a photo has enough pixels to print at a given size and DPI
- Find the exact pixel dimensions a print shop needs for any cm size
- Designers and pre-press: set canvas size in pixels before exporting
- Photographers: confirm a camera's megapixels cover the target print size
- Convert a print size in cm to pixels at 72, 150 or 300 DPI
- Plan large-format banners and posters at 150 DPI without oversizing files
Worked example: 10×15 cm photo at 300 DPI
- Convert cm to inches: 10 ÷ 2.54 = 3.937 in wide, 15 ÷ 2.54 = 5.906 in tall
- Multiply by DPI: 3.937 × 300 = 1181 px, 5.906 × 300 = 1772 px
- Megapixels: 1181 × 1772 ÷ 1,000,000 = 2.09 MP
How it works
2 min readThe formula
The number of pixels you need to print depends on the physical size and the DPI (dots per inch):
Pixels = (centimeters ÷ 2.54) × DPI
The ÷ 2.54 converts centimeters to inches (1 inch = 2.54 cm), and DPI is how many pixels are printed per inch. Do it once for width and once for height. To go from pixels to a print size, reverse it: cm = (pixels ÷ DPI) × 2.54.
Pixels needed at 300 DPI (print standard)
| Print size (cm) | Inches | Pixels (W × H) | Megapixels |
|---|---|---|---|
| 9 × 13 | 3.5 × 5.1 | 1063 × 1535 | 1.6 MP |
| 10 × 15 | 3.9 × 5.9 | 1181 × 1772 | 2.1 MP |
| 13 × 18 | 5.1 × 7.1 | 1535 × 2126 | 3.3 MP |
| 15 × 20 | 5.9 × 7.9 | 1772 × 2362 | 4.2 MP |
| 20 × 30 | 7.9 × 11.8 | 2362 × 3543 | 8.4 MP |
| 21 × 29.7 (A4) | 8.3 × 11.7 | 2480 × 3508 | 8.7 MP |
| 30 × 40 | 11.8 × 15.7 | 3543 × 4724 | 16.7 MP |
| 30 × 45 | 11.8 × 17.7 | 3543 × 5315 | 18.8 MP |
| 50 × 70 | 19.7 × 27.6 | 5906 × 8268 | 48.8 MP |
DPI standards by use
| DPI | When to use |
|---|---|
| 300 DPI | Photo prints, magazines, business cards, fine-art — anything viewed up close |
| 150 DPI | Large posters and banners viewed from 1–2 m away |
| 96 DPI | Standard Windows / monitor display |
| 72 DPI | Web and screen graphics |
How much DPI a banner really needs
Viewing distance is what matters. A 2×1 m banner read from 3 metres away looks perfectly sharp at 100–150 DPI, while a brochure held in your hand needs 300 DPI. Printing a banner at 300 DPI just bloats the file with detail no one can see.
Key point: DPI does not add pixels
Changing an image's DPI tag in software does not create new detail. If a file is 1000×1000 px, it is 1000×1000 px whether you label it 72 or 300 DPI — DPI only sets how large those existing pixels print. To print bigger and sharper you need a higher-resolution original, not a relabel.
Frequently asked questions
How many pixels do I need to print at 300 DPI?
Use pixels = (cm ÷ 2.54) × 300. A 10×15 cm photo needs 1181×1772 px (2.1 MP); an A4 page (21×29.7 cm) needs 2480×3508 px (8.7 MP); a 30×40 cm print needs 3543×4724 px (16.7 MP).
What is the exact DPI-to-pixels formula?
Pixels = (centimeters ÷ 2.54) × DPI for each dimension, since 1 inch = 2.54 cm. If your size is already in inches, simply multiply inches × DPI. To reverse it: cm = (pixels ÷ DPI) × 2.54.
How many megapixels do I need to print a 10×15 cm photo?
About 2.1 MP at 300 DPI (1181×1772 px). For 13×18 cm you need ~3.3 MP, for 20×30 cm ~8.4 MP, and for 30×40 cm ~16.7 MP. Any modern phone camera (12 MP+) easily covers standard photo sizes.
Why 300 DPI for printing?
At normal reading distance (about 30 cm) the human eye can resolve roughly 300 dots per inch, so 300 DPI is the point where more resolution adds no visible sharpness. It became the print and magazine standard for exactly that reason.
Does increasing the DPI value improve a low-resolution image?
No. Changing the DPI tag does not add real detail. A 1000×1000 px image stays 1000×1000 px; relabeling it 300 DPI just makes those same pixels print smaller, or stretching them larger makes the print blurry. You need a higher-resolution original.
What DPI do I need for a large banner?
150 DPI is enough for banners and posters viewed from 1–2 metres, and 100 DPI works for billboards seen from far away. Reserve 300 DPI for anything held in the hand. Printing a banner at 300 DPI only creates an oversized file with detail no one can see.
How do I convert pixels back to a print size?
Use cm = (pixels ÷ DPI) × 2.54. A 4000×3000 px image at 300 DPI prints about 33.9×25.4 cm; at 150 DPI it prints double the size, about 67.7×50.8 cm (with lower sharpness).
Is DPI the same as PPI?
In everyday use they are treated as the same number for this calculation. Technically PPI (pixels per inch) describes the digital image and DPI (dots per inch) describes the printer's ink dots, but the pixels-needed formula uses the same value either way.
Should I export in CMYK or RGB for printing?
Use CMYK for offset and commercial printing so colors match the press; RGB is for screens. Resolution (DPI) and color mode are independent — set 300 DPI and CMYK separately. Many photo labs still accept RGB, so check with your print shop.
Does this calculator store my data?
No. The calculation runs entirely in your browser; nothing is uploaded or saved.