Print resolution (DPI)
What is print resolution (DPI)?
Print resolution, measured in DPI, is how many dots a press lays down per inch, and therefore how many pixels a file needs at its final size. Anything read at arm’s length is prepared at 300 dpi. A banner, a sign or a billboard is seen from metres away and needs far fewer dots. Vector logos and text have no resolution at all and stay sharp at any size.
Example
The arithmetic is one line: pixels = millimetres ÷ 25.4 × dpi. A business card at 85×55 mm and 300 dpi needs a file of 1004×650 pixels. A roll-up banner at 85×200 cm, built at full size and 120 dpi, needs 4016×9449 pixels. A 4×3 m billboard is read from 20 metres or more, so 25 dpi at final size is enough — that is 3937×2953 pixels, about what a phone camera produces. Build the artwork at 1:10 and the required dpi multiplies by ten: the same banner at scale needs 1200 dpi to come out the same.
Why it matters for a business
A logo pulled off a website is usually around 500 pixels wide. That is fine for an online ad and useless for a roll-up: stretched across 85 cm it works out under 15 dpi, and the edges break up as soon as someone stands close. The opposite mistake costs too — an 8,000-pixel photo on a billboard looks no better and produces a file the press handles slowly. A raster image cannot be enlarged: interpolation adds pixels, not detail. So for print we ask the photographer for the originals, and logos and headlines stay vector.
How to improve it
- Build artwork at final size; if you work to scale, put the scale in the file name.
- Ask the photographer for the original files, not the versions resized for the website.
- Keep logos and type as vectors, and rasterise only the effects that force it.
- Match dpi to viewing distance: 300 up close, 100–150 for posters and roll-ups, 20–40 for billboards.
- Check the file at 100% on screen, not at 25%.
Files for banners, signs and billboards are prepared as part of advertising materials.