Minimum Halftone Dot

The diameter of a halftone dot of a given percentage at your screen ruling, and the lowest coverage that the smallest dot your plate can hold gives. You enter the minimum dot yourself.

Screen and dot

Screen rulinglpi

Coverage (dot percentage)%

Smallest dot of the plate, diameterµm

Take the value from your platemaker's data. There is no built-in table of what a plate can hold.

solid circle: your dot
dashed circle: the plate's smallest dot

The dot is smaller than the minimum: it may not print.

Dot diameter

27.0 µm

Screen cell

0.1693 mm

distance between the dot centres

Lowest coverage

2.47%

that the plate's smallest dot gives

How it is calculated

The screen cell p = 25.4 ÷ lpi (mm). A dot covering the share a of the cell has the diameter d = p × √(4a ÷ π).

The other way round, a smallest dot of diameter d_min gives a coverage of at least a_min = π × d_min² ÷ (4 × p²). The plate may not carry smaller percentages.

p = 25.4 / lpi
d = p · √(4a / π)
a_min = π · d_min² / (4 · p²)

Worked example

150 lpi: p = 25.4 ÷ 150 = 0.1693 mm. Coverage 2%: d = 0.1693 × √(0.08 ÷ π) = 27.0 µm.

A smallest dot of 30 µm: a_min = π × 0.03² ÷ (4 × 0.1693²) = 2.47%.

An estimate: a geometrically ideal dot. The real minimum depends on the plate, ink and press: ask your platemaker.

Check a PDF