Dot Gain Calculator - Printed Dot Size After Press Gain

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What dot gain is

Dot gain is the growth of a printed halftone dot beyond its intended size. You ask the press for a 50% dot and you get a 70% dot on paper, because ink spreads as it transfers and soaks into the fibres. The printed picture then looks darker than the file, shadows plug up, and mid-tones lose detail. Every printing process has dot gain; the only question is how much. Measuring it and compensating for it is one of the basic skills of prepress.

Why gain peaks in the middle

Dot gain is not the same at every tone. It is zero at 0% and 100%, where there is no dot edge or no white space left, and it peaks near 50%, where the dot edges are longest relative to the dot area. A press that gains 20% at mid-tone might gain only 8% at 25% and 75%. That curve shape is why a single correction number never fits: a file needs a curve that compensates more in the middle and less at the ends. This calculator models that curve with a smooth shape that peaks at 50%.

How to use this calculator

Enter the dot percentage from your file and pick the press type. Coated stock typically gains around 15% at mid-tone, uncoated around 22% and newsprint around 30%, because rougher, more absorbent paper spreads ink further. The tool returns the gain at your tone and the printed dot size. If you enter 50% on a newsprint setting and get 80% out, your mid-tones will print much darker than planned, and you should lighten the file or apply a compensation curve before plating.

Mechanical versus optical gain

Part of dot gain is mechanical: ink physically spreads beyond the plate dot. Part is optical: light enters the paper, scatters under the dot and gets absorbed, which makes the dot look bigger than it is even when it is not. Optical gain depends on the paper’s translucency and cannot be fixed by changing the plate alone. That is why two papers with the same mechanical gain can still print differently, and why the only reliable check is a printed proof on the real stock.

Compensating for gain

Printers compensate with dot-gain curves, often called plate curves, applied when the plates are made. If the press gains 20% at mid-tone, the plate is made with a 30% dot where the file asks for 50%, so the printed result lands back at 50%. Modern workflows store one curve per press and paper combination and apply it automatically. If you prepare files for a printer, ask whether they apply their own curve; if they do, send uncompensated files, or you will correct twice and end up too light.

Measuring your own press

To measure gain, print a test strip with known dot values, from 5% to 95% in steps, and read the printed values with a densitometer. Plot the difference between asked and printed values to get your curve. Repeat on each paper you use, because the curve moves with the stock. A single test sheet per paper is cheap insurance against an entire run printing dark, and it gives you the real maximum gain number to enter in this calculator instead of a textbook estimate.

Common mistakes

The most common mistake is compensating twice, once in the file and once at the printer. Another is using a coated-paper curve on uncoated stock, which under-corrects and prints dark. A third is judging gain on screen, where dots cannot spread. Measure on the real paper, use one curve per press and stock, and proof mid-tones before the full run.

Dot Gain Calculator – Printed Dot Size After Press Gain