How to Use This Calculator
- Choose your paint type — acrylic, lacquer, or enamel — and brand. This affects the thinner-compatibility note.
- Select your nozzle size — the size affects how thick the mix can safely be. A 0.2 mm nozzle clogs with thick paint; a 0.5 mm nozzle handles more viscous material.
- Set your total cup fill — how many mL you want to put in the airbrush cup in total (paint + thinner combined). You can also enter drops directly.
- Enter your paint:thinner ratio — e.g. 1:1.5 means 1 part paint to 1.5 parts thinner by volume.
- Hit Calculate — get drop counts, ml volumes, a PSI band, a consistency note, and a thinner compatibility warning.
- Optionally open Coverage estimator to get a rough sense of whether your mix volume will cover your model scale.
Paint:Thinner Ratio Reference
These are community-validated starting points. Always do a test pass on a sprue before touching the model.
| Paint type | Application | Typical ratio (thinner:paint) | Notes |
|---|---|---|---|
| Acrylic (Tamiya) | Base coat | 1:1 to 1.5:1 | Use X-20A or lacquer thinner |
| Acrylic (Vallejo) | Base coat | 1:1 to 2:1 | Vallejo Airbrush Thinner preferred |
| Lacquer (Mr. Color) | Base coat | 1.5:1 to 2:1 | Mr. Color Thinner / Levelling Thinner |
| Lacquer (any) | Fine detail | 2:1 to 3:1 | Levelling thinner slows dry time |
| Enamel (Humbrol) | Base coat | 1:1 | White spirit or enamel thinner |
| Acrylic (any) | Filter / wash | 4:1 to 8:1 | Very thin; multiple light passes |
| Varnish / clear | Any | 0.5:1 to 1:1 | Over-thinning causes silvering |
The Formula
Total mix volume (mL) = cups fill input (mL)
Paint volume (mL) = Total × [ratio_paint / (ratio_paint + ratio_thinner)]
Thinner volume (mL) = Total × [ratio_thinner / (ratio_paint + ratio_thinner)]
Flow improver drops = ROUND(total_mix_in_drops / 20) [if enabled]
Drop count = volume_mL / 0.05 (1 drop ≈ 0.05 mL, standard dropper)
Drop volume assumes a standard hobby pipette or dropper bottle (≈ 0.05 mL/drop, 20 drops/mL). Dropper tips vary — calibrate yours against a known volume if precision matters.
Nozzle Size & PSI Quick Guide
| Nozzle | Best for | PSI range | Max safe viscosity |
|---|---|---|---|
| 0.2 mm | Super fine lines, tiny details, 1:144 kits | 10–15 PSI | Skim-milk thin only |
| 0.3 mm | Fine detail, camouflage edges, 1:72–1:35 | 12–18 PSI | Skim to semi-skim |
| 0.35 mm | All-round: detail + base coat | 15–20 PSI | Semi-skim milk |
| 0.4 mm | Base coats, 1:35 armour, larger aircraft | 18–25 PSI | Semi-skim to whole milk |
| 0.5 mm | Primer, large vehicle hulls, dioramas | 20–28 PSI | Whole milk |
Frequently Asked Questions
- What is the correct paint to thinner ratio for airbrushing scale models?
- It depends on paint type and nozzle size. Acrylic (Tamiya, Vallejo) works well at 1:1 to 1:2 thinner-to-paint by volume. Lacquers (Mr. Color) tolerate up to 1:3. Enamels generally thin 1:1 to 1:2. Finer nozzles need thinner mixes. The classic test: your mix should flow off a cocktail stick like skim milk for detail, or semi-skim for base coats.
- How many drops of paint should I put in my airbrush cup?
- For a typical 1–2 mL cup session, 10–20 drops of undiluted paint (at 0.05 mL/drop) before adding thinner is a useful starting point. This calculator converts any cup-fill volume into exact drop counts at your chosen ratio, removing guesswork — just dial in your cup fill and ratio above.
- What PSI should I use for airbrushing plastic models?
- 0.2 mm nozzle: 10–15 PSI. 0.35 mm all-rounder: 15–20 PSI. 0.5 mm base coat: 20–28 PSI. High pressure with thin paint causes excessive overspray; low pressure with thick paint causes tip drying and spatter. Always test on a scrap sprue first and dial pressure up gradually.
- Can I use water to thin Tamiya acrylic for airbrushing?
- Yes, but distilled water alone often causes tip drying and poor atomisation. A widely-used community mix is 50% Tamiya X-20A thinner + 50% isopropyl alcohol (71–91%). Tamiya Lacquer Thinner gives even better atomisation and is plastic-safe for Tamiya acrylics.
- What does flow improver do and how much should I add?
- Flow improver (retarder/wetting agent) reduces surface tension, helping paint level before drying and reducing tip drying in warm conditions. Use 1–2 drops per ~20 drops of total mix. Over-use slows drying significantly and can cause paint to bleed into recesses.
- How do I know if my mix is the right consistency?
- Use the milk test: dip a cocktail stick in the mix, let a drop form and fall. For fine detail work, it should flow cleanly like skim milk. For base coats, semi-skim is acceptable. Too thick: it strings or beads. Too thin: it runs off instantly with no body. Always test on white card or a scrap sprue before painting the model.
Ratios and PSI values are community-established guidelines, not manufacturer specifications. Results are estimates for planning purposes. Always test on a scrap surface first. Not professional advice.