DPI calculator
Pixels are not a size until you say how many go in an inch. Type a physical size to get the pixels, or pixels to get the size — either side fills in the other.
What DPI actually means
DPI is dots per inch: how many pixels are packed into each inch of paper. The sum is as simple as it sounds — pixels = inches × DPI. A 5 in edge at 300 DPI is 1500 px. The same 1500 px printed across 10 in is 150 DPI, and looks half as sharp.
So a picture does not have a DPI on its own. A 1500 × 2100 px file is 300 DPI printed at 5 × 7 in, and 72 DPI printed at 20.8 × 29.2 in. It is the same file. What changes is how far you spread it.
The common sizes at 300 DPI
| 5 × 7 in invitation | 1500 × 2100 px |
|---|---|
| 4 × 6 in card | 1200 × 1800 px |
| 8.5 × 11 in (Letter) | 2550 × 3300 px |
| A4 (210 × 297 mm) | 2480 × 3508 px |
| 2 × 2 in sticker | 600 × 600 px |
| 11 × 8.5 in chip bag | 3300 × 2550 px |
Why 300
300 DPI is the number print shops ask for because it is roughly where a normal eye stops seeing individual dots at reading distance. Below it, edges soften and small text goes muddy. Above it, most presses cannot show the difference and the file just gets bigger.
72 DPI is a screen convention, not a print one. A picture saved for a web page is usually far too few pixels to print at the size it appears on screen — which is the usual reason a printed design comes out blurry when it looked fine on the monitor.
Where this goes wrong
- Changing the DPI number without changing the pixels. Setting a file's DPI field to 300 in an image editor, without resampling, does not add detail. It only changes the size it says it should print at.
- Enlarging a small picture. Going from 600 px to 1500 px invents pixels that were never photographed. It will not be sharper than the original.
- Judging sharpness on screen. A monitor shows about 100 pixels to the inch, so everything looks fine zoomed to fit. Print is three times denser.
BoboCreate exports PNG and JPG at whatever DPI you ask for, and a design with a physical size knows its own: a 5 × 7 in card renders at 1500 × 2100 px when you pick 300, without you working it out.