Thinning calculator
Paint to Thinner Ratio Calculator
Tell it how much paint is on the palette and the ratio you want, and it works out exactly how much thinner to add — no guessing, no "add a little until it looks right". The ratio presets are the ranges I reach for at my own bench. They are conventions, not rules, and every number here is a field you can change.
- Exact thinner volume for the paint you actually have
- Milliliters, drops and relative parts from one ratio
- Runs entirely in your browser — nothing you type is uploaded or saved
Ratios I actually reach for
These are starting points from my own bench, written as ranges because that is what they are. The paint in your bottle, the age of it, the humidity in the room and the brush or needle you are using all move the number. Treat the table as somewhere to start, then adjust by what the paint does on the model.
| Thinner | Typical ratio (paint : thinner) | What it is for |
|---|---|---|
| Water | 1:1 to 3:1 (paint : water) | Free, always on the desk, and good enough for most brush work. |
| Airbrush thinner | 1:1 to 2:1 (paint : thinner) | Made to keep pigment suspended and to dry a little slower than water. |
| Flow improver | 8:1 to 20:1 (paint : flow improver) | A surfactant, not a thinner. A few drops per pot breaks surface tension. |
| Glaze / acrylic medium | 1:3 to 1:6 (paint : medium) | Thins the paint while keeping the binder, which is what glazing wants. |
Flow improver is the odd one out: it is a surfactant, not a thinner, and most people add it by the drop to a pot rather than mixing it as an equal partner. Pick water or airbrush thinner when you want the paint thinner, and flow improver when you want it to level out.
How to mix it
- Measure the paint first. Whatever is already on the palette counts. Put that number in the top box.
- Pick the ratio, then read the result. The result panel gives you the thinner in ml and in drops, so you can use a pipette or go straight from the dropper bottle.
- Add thinner to paint, not paint to thinner. You can always add more thinner; you cannot take it back out. Add about two-thirds of the calculated amount, stir, then add the rest.
- Test on a spare base or a thumbnail. If it beads, crawls or spatters, it is too thin. If it drags, dries on the brush or clogs the nozzle, it is too thick.
- Write down what worked. The copy button gives you a plain-text summary you can paste into a notes app next to the paint name.
What this calculator does not do
- It does not measure your paint. It does arithmetic on the numbers you type, which is why every field is editable.
- It does not model air pressure, needle size or paint brand. Those change the right ratio more than the ratio chart does.
- It does not assume a drop size. Drops are converted at 20 drops per ml unless you change that field, because real dropper bottles differ.
- It does not store, send or remember anything. Reload the page and it is back to the defaults.
Questions I get about thinning paint
How much thinner do I add to acrylic paint?
Start from the ratio box above rather than a fixed number. The calculator takes whatever paint amount you actually have and turns the ratio into a volume, so 2:1 on five milliliters is ten drops of thinner, not a vague "a bit". The guidance ranges are conventions I use at the bench, and the paint in your bottle decides more than any chart.
What ratio should I use for airbrushing miniatures?
A common starting point is 1:1 to 2:1 paint to airbrush thinner, then adjust from what you see: spattering usually means too thick, pooling and spidering usually mean too thin. Needle size, air pressure and the paint brand all shift the number, which is why this page never overrides your value.
Can I thin acrylic paint with water instead of thinner?
For brush work, yes — water is fine and it is what most people already have. Water thins the binder as well as the paint, so a very watery mix covers worse and dries chalky. Airbrush thinner and acrylic medium keep more of the binder, which is what you want for airbrushing and glazing.
How many drops are in a milliliter of paint?
About 20 drops per milliliter is the usual convention, which makes one drop roughly 0.05 ml. Real dropper bottles vary a lot, so the drops per ml field is editable: if your bottle gives noticeably fatter drops, measure 20 of them once and put your own number in.
Does thinning paint make it weaker?
Thinner mixes carry less pigment per brush-load, so they cover in more coats and can look chalky when water is doing all the work. Acrylic medium thins the paint while keeping the binder, which is why glazes use medium instead of water. Either way, the calculator tells you the volume, not the opacity — test on a spare base first.