Lexicon: P
ppi
ppi means pixels per inch (1 inch = 2.54 cm). The value indicates how densely the pixels sit in a file and is therefore the measure of resolution.
For large-format printing (at original size 1:1): large formats over 5 m² at least 35 ppi, smaller formats at least 70 ppi, up to a maximum of around 120 ppi. More than 120 ppi brings no visible benefit but makes the file unnecessarily large.
ppi is often equated with dpi. Strictly speaking, ppi refers to the image dots in the file, dpi to the ink droplets of the printing machine – for data preparation the ppi value is what matters.