How many DPI for printing? A short guide
DPI (dots per inch) is the number of dots per inch of print. In photography it is used interchangeably with PPI, the number of image pixels per inch. The more pixels per inch, the sharper the print. The same photo can look great as a 10 × 15 cm print and poor as a poster, because the same pixels are spread over a larger area.
The conversion is simple: print size in inches equals the number of pixels divided by DPI, and you turn inches into centimetres by multiplying by 2.54. Example: a 6000 × 4000 px photo at 300 DPI gives a print of roughly 51 × 34 cm. The calculator above does this automatically in both directions: from pixels to centimetres and from a print format to the resulting DPI.
300 DPI is the gallery-quality standard for prints viewed up close: albums, prints, photo books. 150 DPI is perfectly fine for prints viewed from about a metre, and large-format posters and banners are printed at as little as 72 to 100 DPI, because they are viewed from several metres away. Rule of thumb: the greater the viewing distance, the fewer DPI you need.
How many pixels is 300 DPI?
300 DPI is about 118 pixels per centimetre (300 divided by 2.54). A 10 × 15 cm print at 300 DPI needs 1181 × 1772 px, roughly 2 Mpx, and 13 × 18 cm about 1535 × 2126 px. At 150 DPI half is enough: 591 × 886 px for 10 × 15 cm. The full format table is above.
How many pixels for A4 and A3?
A4 is 21 × 29.7 cm, so at 300 DPI it needs 2480 × 3508 px (about 8.7 Mpx) and at 150 DPI 1240 × 1754 px. A3 is 29.7 × 42 cm: 3508 × 4961 px at 300 DPI (about 17.4 Mpx) and 1754 × 2480 px at 150 DPI. Any modern camera and most phones meet this.
DPI vs PPI: what is the difference?
PPI (pixels per inch) describes the file: how many image pixels fall on one inch of print. DPI (dots per inch) describes the printer: how many ink dots it lays down per inch. Labs and print shops casually say "DPI" when they mean PPI, so this calculator uses that name too. The DPI value stored in the file (e.g. 72 or 300) changes neither the pixel count nor the quality; what matters is the ratio of pixels to print size.