400 DPI in pixels
At 400 DPI an inch is 400 pixels and a centimetre is 157.5 pixels. An A4 page is 3307 × 4677 pixels and a US Letter page is 3400 × 4400.
400 DPI is used for scanning small originals and fine print, and is close to the pixel density of many phone screens.
At 400 DPI the pixels of a print blend together, for someone with 20/20 vision, from about 8.6 inches (22 cm) away. Closer than that, an eye can pick out the pixel grid; further back, more resolution adds nothing you can see.
Paper and photo sizes at 400 DPI
| Size | Dimensions | Pixels at 400 DPI | Megapixels | Uncompressed |
|---|---|---|---|---|
| A0 | 841 × 1189 mm | 13244 × 18724 | 248 | 709 MB |
| A1 | 594 × 841 mm | 9354 × 13244 | 124 | 354 MB |
| A2 | 420 × 594 mm | 6614 × 9354 | 62 | 177 MB |
| A3 | 297 × 420 mm | 4677 × 6614 | 31 | 89 MB |
| A4 | 210 × 297 mm | 3307 × 4677 | 15 | 44 MB |
| A5 | 148 × 210 mm | 2331 × 3307 | 7.7 | 22 MB |
| A6 | 105 × 148 mm | 1654 × 2331 | 3.9 | 11 MB |
| A7 | 74 × 105 mm | 1165 × 1654 | 1.9 | 5.5 MB |
| Letter | 8.5 × 11 in | 3400 × 4400 | 15 | 43 MB |
| Legal | 8.5 × 14 in | 3400 × 5600 | 19 | 54 MB |
| Tabloid | 11 × 17 in | 4400 × 6800 | 30 | 86 MB |
| Half Letter | 5.5 × 8.5 in | 2200 × 3400 | 7.5 | 21 MB |
| 4 × 6 in | 4 × 6 in | 1600 × 2400 | 3.8 | 11 MB |
| 5 × 7 in | 5 × 7 in | 2000 × 2800 | 5.6 | 16 MB |
| 8 × 10 in | 8 × 10 in | 3200 × 4000 | 13 | 37 MB |
| 11 × 14 in | 11 × 14 in | 4400 × 5600 | 25 | 70 MB |
| 16 × 20 in | 16 × 20 in | 6400 × 8000 | 51 | 146 MB |
| 12 × 12 in | 12 × 12 in | 4800 × 4800 | 23 | 66 MB |
| 12 × 18 in | 12 × 18 in | 4800 × 7200 | 35 | 99 MB |
| 18 × 24 in | 18 × 24 in | 7200 × 9600 | 69 | 198 MB |
| 24 × 36 in | 24 × 36 in | 9600 × 14400 | 138 | 396 MB |
| Business card | 2 × 3.5 in | 800 × 1400 | 1.1 | 3.2 MB |
Lengths at 400 DPI
| Inches | Pixels |
|---|---|
| 0.25 in | 100 |
| 0.5 in | 200 |
| 0.75 in | 300 |
| 1 in | 400 |
| 1.5 in | 600 |
| 2 in | 800 |
| 2.5 in | 1,000 |
| 3 in | 1,200 |
| 3.5 in | 1,400 |
| 4 in | 1,600 |
| 5 in | 2,000 |
| 6 in | 2,400 |
| Centimetres | Pixels |
|---|---|
| 0.5 cm | 79 |
| 1 cm | 157 |
| 1.5 cm | 236 |
| 2 cm | 315 |
| 2.5 cm | 394 |
| 3 cm | 472 |
| 3.5 cm | 551 |
| 4 cm | 630 |
| 4.5 cm | 709 |
| 5 cm | 787 |
| 6 cm | 945 |
| 7 cm | 1,102 |
| Millimetres | Pixels |
|---|---|
| 1 mm | 16 |
| 2 mm | 31 |
| 3 mm | 47 |
| 5 mm | 79 |
| 10 mm | 157 |
| 15 mm | 236 |
| 20 mm | 315 |
| 25 mm | 394 |
| 30 mm | 472 |
| 35 mm | 551 |
| 40 mm | 630 |
| 45 mm | 709 |
Changing an image to 400 DPI
The DPI stored in an image file is a label that says how large to print it. Changing the label to 400 without resampling keeps every pixel and only changes the print size: a 3000 × 2000 pixel photo becomes 7.5 × 5 inches. Resampling changes the number of pixels instead, and making an image larger that way does not add detail.