Screen Printing Calculator

Screen printing depends on a few physical relationships: how fine the mesh is, how fine the halftone dots in the artwork are, and how much light the emulsion needs. Getting them wrong leads to lost detail, moiré patterns or under-exposed stencils that wash out. This calculator covers the usual numbers.

Mesh count

Mesh count is the number of threads per inch, or per centimeter in much of Europe and Asia. The tool converts between them: 120 threads per cm equals about 305 per inch. Low counts, 40 to 60 per cm, deposit thick ink for textiles and bold graphics. High counts, 100 to 150 per cm, hold fine detail and halftones for paper and posters.

Matching halftones to mesh

A halftone dot must sit on enough threads to print reliably. The common rule says the mesh count should be four to five times the halftone frequency in lines per inch. For a given mesh the tool shows the workable lpi range, and for a given lpi the mesh you need, about 4.5 times. A 230-per-inch mesh handles roughly 46 to 58 lpi; a 45 lpi image wants about 200 threads per inch.

Finest printable line

Lines narrower than about two mesh openings tend to break up or disappear. The tool calculates that limit in millimeters for your mesh, so you can check the thinnest strokes in logos and text before burning a screen.

Avoiding moiré

When the regular grid of halftone dots interferes with the regular grid of the mesh, a wavy moiré pattern appears. Angle the halftone at about 22.5 degrees to the mesh threads, or tilt the screen when stretching, and avoid mesh-to-lpi ratios that are whole numbers. Many printers output halftones at 22.5 degrees for single-color work for exactly this reason.

Exposure and lamp distance

Once you have found a good exposure time at one lamp distance, the tool rescales it for a new distance using the inverse square law. Doubling the distance needs four times the exposure. Exposure calculators and step wedges are still the best way to find the base time for your emulsion and lamp; then this calculation keeps it consistent after changes.

Preparing artwork

Separate each color into its own black positive, add registration marks, and output halftones at a line count suited to the mesh. The Posterize Image tool helps plan a limited color palette, and the Image Dithering Tool can generate halftone dot screens with a chosen spacing and angle.

Printing positives

Print positives on inkjet transparency film as densely black as possible; any gray lets light through and weakens the stencil. Two stacked, aligned positives can help with weak printers.

Practical checklist

Degrease the mesh before coating, coat evenly and dry in the dark, expose with good contact between film and screen, wash out gently, and check fine details against the light before printing.

Mesh for common jobs

T-shirts with bold plastisol designs usually use 110 to 160 threads per inch. Water-based inks and finer textile detail use 160 to 230. Posters and paper prints with halftones use 230 to 305. Very fine detail on hard surfaces and UV inks can go higher.

Related tools

For other inverse-square light calculations, see the Flash Exposure Calculator. For contact printing negatives in alternative processes, use the Digital Negative Maker.