The one formula: pixels = inches × DPI
DPI (dots per inch) describes how densely an image is printed, not how many pixels it contains. That is why a search for "300 DPI in pixels" has no single answer on its own — you also need the physical size. Combine the two and the pixel count follows from one formula:
pixels = inches × DPI
A 4×6 inch photo at 300 DPI is 1200×1800 pixels (4 × 300 = 1200, and 6 × 300 = 1800). The same 4×6 photo at 72 DPI is only 288×432 pixels. The print size did not change; the pixel count did, because DPI is pixels packed into each inch of paper.
The formula rearranges two useful ways. To find the print size a file can fill, divide: inches = pixels ÷ DPI. To find the density a fixed image will print at, divide the other way: DPI = pixels ÷ inches.
DPI to pixels chart (inches)
Pixel dimensions for the most common photo and paper sizes, at the four DPI values people search for most. Find your print size on the left, then read across to the DPI you need.
| Print size | 72 DPI | 150 DPI | 300 DPI | 600 DPI |
|---|---|---|---|---|
| 2×2 in (passport) | 144×144 | 300×300 | 600×600 | 1200×1200 |
| 3.5×5 in | 252×360 | 525×750 | 1050×1500 | 2100×3000 |
| 4×6 in | 288×432 | 600×900 | 1200×1800 | 2400×3600 |
| 5×7 in | 360×504 | 750×1050 | 1500×2100 | 3000×4200 |
| 8×10 in | 576×720 | 1200×1500 | 2400×3000 | 4800×6000 |
| 8.5×11 in (Letter) | 612×792 | 1275×1650 | 2550×3300 | 5100×6600 |
| 11×14 in | 792×1008 | 1650×2100 | 3300×4200 | 6600×8400 |
DPI to pixels chart (cm, mm and A-sizes)
For metric sizes the formula is pixels = mm ÷ 25.4 × DPI, because one inch is 25.4 mm. These are the pixel dimensions at the 300 DPI print standard. For 150 DPI, halve each number; for 600 DPI, double it.
| Size | Pixels at 300 DPI |
|---|---|
| A6 (105×148 mm) | 1240×1748 |
| A5 (148×210 mm) | 1748×2480 |
| A4 (210×297 mm) | 2480×3508 |
| A3 (297×420 mm) | 3508×4961 |
| 10×15 cm | 1181×1772 |
| 13×18 cm | 1535×2126 |
| 15×20 cm | 1772×2362 |
| 20×30 cm | 2362×3543 |
Reverse: pixels to print size
To go the other way — you have an image and want to know how large it can print — divide the pixel dimensions by the DPI you want. At the 300 DPI standard, these are the largest sizes each common resolution can fill without dropping below print quality.
| Pixels | Max print at 300 DPI |
|---|---|
| 1080×1080 | 3.6×3.6 in (9.1×9.1 cm) |
| 1920×1080 | 6.4×3.6 in (16.3×9.1 cm) |
| 2048×1536 | 6.8×5.1 in (17.3×13 cm) |
| 3000×2000 | 10×6.7 in (25.4×16.9 cm) |
| 4000×3000 | 13.3×10 in (33.9×25.4 cm) |
| 6000×4000 | 20×13.3 in (50.8×33.9 cm) |
Which DPI should you use?
Higher DPI is not automatically better — it only adds pixels, and past a point the eye cannot resolve them at normal viewing distance. Match the density to the job.
| DPI | Best for |
|---|---|
| 72 / 96 DPI | Screen presets (historical). Browsers ignore the tag; only pixels matter online. |
| 150 DPI | Draft prints, and large posters or banners viewed from a distance. |
| 300 DPI | The photo and document print standard — sharp at arm's length. |
| 600 DPI | Line art, small text, fine detail, and archival scans. |
A caution: DPI does nothing on screens
These charts are for print. On a screen, the DPI tag stored in a file is ignored completely — a browser displays an image by its pixel dimensions and the CSS layout, nothing else. Changing a file from 300 DPI to 72 DPI without resampling leaves the on-screen result, and the file size, identical. So if your goal is web display rather than print, skip the DPI math and think only in pixels.