Miniature Painting Dilution and Airbrush PSI Calculator

What this estimate does and does not do

This calculator gives a starting recipe for miniature airbrushing: thinner-to-paint ratio, thinner drops, optional flow improver, PSI range, and spray distance. It is meant for common hobby acrylics, primers, varnishes, inks, and metallics used on miniatures, models, terrain, and wargaming pieces.

It does not replace product instructions or test spraying. Every paint line behaves differently. Some primers and varnishes should only be thinned with the manufacturer’s recommended product. Solvent-based lacquer or enamel systems need different reducers, ventilation, respirators, and cleaning chemistry. Always spray in a ventilated area, avoid inhaling aerosolised paint, and follow the safety data sheet for the specific product.

Formula / method used

The calculator starts with a base thinner-to-paint ratio for the paint type, then adjusts it for technique and nozzle size.

The output drops are then scaled from your paint amount:

For PSI, the calculator starts from a nozzle-size pressure, then adjusts for the paint and technique:

The result is shown as a small PSI range because regulator accuracy, hose losses, paint thickness, humidity, and trigger control vary.

Rule-of-thumb settings used

Typical starting points behind the calculator:

• 0.2 mm fine detail: thinner paint, about 10–15 PSI
• 0.3 mm general miniature work: milk-like acrylic mix, about 15–20 PSI
• 0.4–0.5 mm primer/varnish/terrain work: slightly thicker mix, about 20–30 PSI
• Standard hobby acrylic: around 1:1 thinner-to-paint through a 0.3 mm nozzle
• Thick brush acrylic or fine detail: more thinner
• Airbrush-ready paint, inks, and contrast-style paints: little extra thinner
• Primer and varnish: often use a larger nozzle and follow the product label

Worked example

For a standard hobby acrylic basecoat through a 0.3 mm nozzle with 10 drops of paint and 10% flow improver:

The starting pressure is about:

Test the mix on paper or a spare model. If it sputters, add a little thinner or raise PSI slightly. If it spiders or floods, lower PSI, move farther away, or thicken the mix slightly.

How to tune after the first test spray

• Sputtering / clogging: add thinner or medium one drop at a time, raise PSI slightly, clean the tip, or use a larger nozzle.
• Spider-webbing / runny paint: lower PSI, move farther from the model, use less thinner, or apply lighter passes.
• Dusty / grainy finish: paint may be drying before it lands; lower PSI, move closer, add a little retarder/flow improver, or reduce distance.
• Weak coverage: reduce thinner, use more coats, or switch from glaze settings to basecoat settings.
• Frequent primer clogs: use a 0.3–0.5 mm nozzle, strain the primer, and thin only with a compatible thinner.

Assumptions and limitations

• Ratios are by drops/parts, not precise weight or viscosity measurement.
• Drop size varies by bottle, pipette, and paint thickness.
• Flow improver is treated as an extra additive, not a replacement for thinner.
• Paint age, pigment, metallic flakes, primer solids, humidity, temperature, and compressor pulsing all affect the result.
• The calculator assumes water-based hobby acrylic workflows. Lacquers, enamels, urethanes, and solvent reducers require product-specific guidance.
• PSI is a regulator starting point; actual pressure at the nozzle can differ.

For another hobby-materials calculator, see the Cross-Stitch Fabric and Thread Calculator. If you are building terrain or wood bases, the Wood Movement Predictor may also help.