Screen Ruling to Resolution (lpi → ppi)

The image resolution you need for a given halftone screen. The rule: 1.5–2 pixels per screen line.

Screen ruling

Screen rulinglpi

Factor (pixels per line)

Usually 2; at least 1.5. A larger factor leaves a margin of quality and makes a larger file.

Image size on the print

Image widthmm

Resolution needed

300 ppi

ppi (pixels per inch)

Screen ruling in lpi

150.0 lpi

Screen ruling in lines/cm

59.1 lines/cm

Pixels across

1 181

for the image width above

How it is calculated

For a clean halftone dot the image needs 1.5–2 pixels per screen line: ppi = lpi × factor. Usually 2 is used.

One line/cm equals 2.54 lpi. Pixels for a size: pixels = mm ÷ 25.4 × ppi.

ppi = lpi · factor
lpi = lines/cm · 2.54
pixels = mm / 25.4 · ppi

150 lpi at factor 2 → 300 ppi.

50 lines/cm × 2.54 = 127 lpi → 254 ppi at factor 2.

A rule of thumb: confirm the resolution you need with your printer.