What is LPI in printing?
LPI, lines per inch, is the screen ruling of a halftone: how many rows of dots fit in an inch, so a higher lpi gives finer, smoother photos and tints.
What it means for your file
The printer sets it for the press and paper; it is not the same as an image’s ppi or a printer’s dpi. As a rough guide: about 85 lpi for newspapers, 133 to 150 lpi or more for offset work on coated paper, and much coarser for screen printing. Uncoated papers usually get a coarser screen than coated ones, because the dots spread more as the ink soaks in.
How the dots themselves work: see halftone. To check an image’s resolution at its printed size, use the DPI calculator.
An example
A brochure printed offset at 150 lpi has 150 rows of halftone dots in every inch, too fine to see without a magnifier, and its photos are supplied at about 300 ppi, twice the ruling. The same photo screen printed at around 55 lpi shows its dots clearly, which is why screen printers ask for simpler artwork and bolder tones.
A common mistake
Mixing up lpi, dpi and ppi. PPI is the pixels in your image, dpi is the dots a printer or platesetter can place, and lpi is the halftone screen built from those dots. Raising an image far beyond about twice the lpi adds file size, not sharpness. For screen printing, ask the shop which lpi they use before the halftones are made.
Related terms
All print terms in the glossary, or run your file through the free print-ready checker.
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