Airbrush Paint Thinning Ratio Calculator

How the airbrush thinning ratio calculator works

1. Measure the paint. Enter the neat paint volume in millilitres. A graduated mixing cup or a dropper bottle with ml markings keeps this step honest.
2. Pick the ratio. The ratio is paint to thinner by volume, so 1:2 means one part paint and two parts thinner. This calculator covers the 1:1 to 1:4 range.
3. Set your working pressure. The slider covers 15–30 PSI, the band used in this site's airbrush guides. Lower pressure often needs a thinner mix to atomise cleanly, but the paint and nozzle instructions, plus a test spray, decide what is suitable.
4. Add flow improver only if your product calls for it. Here it is counted on top of the paint + thinner base at the share you choose. Whether it can stand in for part of the thinner, and whether to use it at all, varies by product: some lines treat it as an additive, some include it in their thinning guidance, and others say to leave it out. Follow the label.

What the result tells you

The paint, thinner and flow-improver rows are the amounts to put in the cup, in millilitres and in drops. The mixed volume is what you end up with after thinning, which is the number to check against your cup or colour cup capacity before you start. The ratio row repeats the mix you selected. The note underneath compares it with a generic starting suggestion for the pressure you set; that suggestion is not a universal recipe, and the paint, nozzle and product instructions take precedence.

Drops are converted at 20 drops per millilitre. That is a hobby convention rather than a measured drop size, so treat the millilitre figures as exact and the drop counts as a convenience when you are working straight from a dropper bottle.

Generic starting suggestions by working pressure

The table is a set of optional starting points for a test spray, not a rulebook. Paint brands, nozzle sizes and even colours within one range thin differently, so check the product instructions and adjust from what actually sprays cleanly.

Worked example

You have measured 5 ml of paint and you choose a 1:2 mix at 20 PSI. The calculator follows your ratio: 5 ml of paint plus 10 ml of thinner, which mixes to 15 ml. Switch on the flow improver at the default 5% of the paint + thinner base and it adds 0.75 ml, bringing the cup to 15.75 ml — about 315 drops in total at an estimated 20 drops per millilitre. If your paint's instructions specify a different ratio, use that ratio in the selector.

What this calculator does not do

• It does not know your paint line, thinner or nozzle, and it does not recommend one ratio as universally suitable. A manufacturer's own thinning instructions and a test spray come first; the pressure table is only a set of generic starting suggestions.
• It only covers the 15–30 PSI working band. Pressures below or above that range need their own testing on your airbrush and nozzle.
• It does not judge finish, coverage or drying time, and it cannot tell you whether flow improver suits your product. Change one variable at a time and spray a test card before committing to a model.
• It never sends or stores your numbers. Everything is calculated in this page, in your browser.

Frequently asked questions

What ratio should I start with for airbrushing miniatures?

There is no universal ratio. Pick the ratio you intend to use, or the one your paint and nozzle instructions specify, and the calculator works out that mix. 1:2 at around 20 PSI is only one common starting suggestion in the 15-30 PSI band used in this site's guides; test it on scrap and adjust for your paint, airbrush and nozzle.

How many drops are in 1 ml of paint?

This calculator estimates 20 drops per millilitre, a common hobby convention rather than a measured drop size. Real drops change with paint viscosity, nozzle size and how hard you squeeze the dropper bottle, so the millilitre amounts are the exact figures and the drop counts are an estimate.

Does flow improver count as thinner?

That depends on the product. Some lines recommend flow improver as an additive alongside thinner to slow tip dry, some include it in their thinning guidance, and others advise against it or say not to substitute it for thinner. The calculator treats it as an optional additive at a percentage of the paint + thinner base (5% by default), but the product label decides whether and how much to use.

Can I use this calculator with any paint brand?

It calculates the mix for the ratio you choose, but it does not declare that ratio suitable for every paint. Many water-based acrylics can be airbrushed, yet each paint line and nozzle has its own guidance. If the manufacturer specifies a ratio, a dedicated thinner or a flow improver routine, follow that and confirm with a test spray.