print DPI Converter (Pixels ↔ mm ↔ inches) star

How It's Calculated

The bridge between screen pixels and physical print size is: px = inches × DPI = mm ÷ 25.4 × DPI. At 300 DPI (the standard for offset and professional photo printing), an A4 sheet (210×297 mm) needs 2,480×3,508 px; a 10×15 cm photo needs 1,181×1,772 px. At 150 DPI (general office and brochure printing, or large posters viewed from a distance) the pixel requirement halves; 72 DPI was a historical screen standard and is not sufficient for print output — it looks visibly soft or blocky on paper.

The calculation works backwards too: a 4,000×3,000 px photo prints sharp at the 300 DPI photographic-quality threshold up to 33.9×25.4 cm (4000 ÷ 300 = 13.3 in = 33.9 cm). Push the same file to a poster size of 60×90 cm and the effective resolution drops to roughly 169 DPI — still acceptable for large-format print viewed from a few meters away, but not for a close-up brochure. Common DPI targets: 300 for brochures, magazines and professional photo prints, 150 for general office printing and posters, 100-120 for banners and billboards viewed from a distance, and 600 for fine technical line art.

What to Know

• DPI is a print concept; PPI is a screen concept. Dots Per Inch describes physical ink/toner dots a printer lays down; Pixels Per Inch (see the dedicated screen-PPI calculator) describes pixel density on a display. The two get used interchangeably in casual conversation, but they answer different questions — DPI answers "will this print sharp," PPI answers "does this look sharp on this screen."
• Quality thresholds aren't arbitrary. 300 DPI is the professional photo-print benchmark because it is roughly the finest detail the human eye resolves at normal reading distance; 150 DPI suffices for general brochures and posters viewed a bit further away; 72 DPI is a historical screen-resolution figure (from early low-density displays) that is far too coarse for any printed output — an image that looked fine on an old-standard screen will look pixelated on paper.
• Raising the DPI number in image-editing software without resampling only changes the intended print size in the file's metadata — it does not add real detail. The pixel dimensions captured or exported are the actual ceiling on print quality; upsampling (inventing new pixels) improves this only marginally.