How It Works
This calculator works in 4 steps.
Enter the paint volume
Type the paint amount in fl oz, quarts, gallons, mL, or L.
Enter the reduction
Type the percent or ratio from the product data sheet.
Read the thinner amount
The calculator multiplies paint volume by the reduction fraction.
Check the final mix share
The calculator shows thinner as a percent of the total mix.
The Formula
The formula multiplies the paint volume by the reduction fraction.
V_thinner = V_paint × (r / 100)1 : (100 / r) thinner to paint% = 100 × r / (100 + r)- r:
- Reduction percent of paint volume
- V_paint:
- Paint volume
Reducing 1 US gallon of oil-based enamel by 10% adds 12.8 fl oz (379 mL) of mineral spirits. Thinner forms 9.1% of the final mix.
Conversion Table
The conversion table gives thinner per gallon and per liter of paint for 5 reduction levels.
| Reduction | Thinner:paint | Per US gallon of paint | Per 1 L of paint | Thinner share of mix |
|---|---|---|---|---|
| 5% | 1:20 | 6.4 fl oz | 50 mL | 4.762% |
| 10% | 1:10 | 12.8 fl oz | 100 mL | 9.091% |
| 15% | 1:6.667 | 19.2 fl oz | 150 mL | 13.04% |
| 20% | 1:5 | 25.6 fl oz | 200 mL | 16.67% |
| 25% | 1:4 | 32 fl oz | 250 mL | 20% |
What Is the Paint Thinner Ratio Calculator?
The Paint Thinner Ratio Calculator is a tool that applies a manufacturer-specified reduction, such as "reduce up to 10% with mineral spirits", to a measured amount of paint and returns the thinner amount. Paint reduction percent refers to the paint volume, so 10% reduction of 1 gallon adds 12.8 fl oz of thinner.
Reduction affects film thickness, flow, and spray pattern. The product data sheet sets the thinner type and the maximum reduction, which often differs between brushing and spraying. The calculator applies the stated percent and reports the thinner share of the final mix.
Common Uses
There are 5 main uses of this calculator.
Spray painting
Painters reduce paint to the sprayer's viscosity range.
Brushing
Users thin paint slightly for flow in warm weather.
Primers
Painters reduce primers per data sheet limits.
Furniture finishing
Finishers thin varnish for wiping coats.
VOC checks
Contractors check that reduction stays within VOC limits.