Paint Thinner Calculator
Written by Thierno Sadou Diallo, formula verified per our methodology • Last checked on 10/10/2026
The volume of thinner to add is calculated with paint volume × dilution percentage. For 5 L of paint diluted at 10%, you need to add 0.5 L of thinner.
Explanation
Thinning a paint means slightly reducing its viscosity to make it easier to apply, especially with a spray gun, where a too-thick paint easily clogs the nozzle or produces a grainy finish. The dilution percentage needed varies greatly depending on two factors: the type of paint (an oil-based paint and a water-based acrylic paint are not thinned with the same product or in the same proportions) and the application method chosen, with spray guns generally requiring more thinning than a roller or brush. A range of 5 to 15% is commonly cited by manufacturers, but the product's technical data sheet remains the most reliable reference for this figure, specific to each paint. Excessive thinning degrades the paint's coverage (more coats are then needed for an opaque result) and can also reduce the durability of the final film; insufficient thinning, conversely, leaves roller marks or clogs a spray gun. Once the right dilution has been found for one can, the same proportion can be reproduced for the following cans of the same paint, provided you consistently use the thinner recommended by the manufacturer (water for an acrylic paint, white spirit for an oil-based paint, for example) rather than a generic product. For the total amount of paint needed before thinning, see also our paint quantity calculator; the same thinning principle also applies to a wood stain or varnish, see our wood stain or varnish quantity calculator.
Example: 5 L of paint diluted at 10%
Inputs
Paint volume: 5 L. Dilution: 10%.
Calculation
Thinner = 5 × (10 ÷ 100) = 0.5 L.
Result
You need to add 0.5 L of thinner to these 5 L of paint.
Frequently asked questions
Which thinner should I use for my paint?
This depends entirely on the type of paint: water works for an acrylic paint (water-based), while an oil-based paint (solvent-based) needs a specific thinner such as white spirit. Using the wrong thinner can curdle the paint or compromise its finish once dry — always check the manufacturer's instructions on the can.
What happens if I thin my paint too much?
Excessive thinning reduces the amount of pigments and binders per unit of applied volume, which decreases the paint's coverage (hiding power): more coats are then needed for an opaque, even result, and the final film may be less durable and less resistant than paint applied at the correct concentration.
Should I thin more for a second coat?
Generally no: unless the manufacturer states otherwise, the same dilution applies to all coats of the same paint. Some professionals thin the very first primer coat slightly more on a highly absorbent surface, but this practice remains specific to the surface and product, to be confirmed with the technical data sheet rather than applied systematically.