The calculator
Runs in your browser. Ratios with decimals work: 100 : 10, or 1 : 0.5.
How the batch is worked out
A ratio of A : B : C splits the batch in parts. Each component is total × its parts ÷ sum of parts. At 4 : 1, a 500 mL batch is 400 mL base and 100 mL activator.
From the base on hand, the total is base × sum ÷ parts of A: a 400 mL tin at 4 : 1 makes 500 mL. From an area, the volume is area × wet film: 1 m² at 1 µm wet is exactly 1 mL, so 2 m² at 50 µm is 100 mL before losses.
Volume and weight are not interchangeable. A ratio given by weight (common for sealants) uses the scale; one given by volume uses graduated cups. Converting between them needs both densities from the data sheet.
Worked example
An epoxy primer at 4 : 1 by volume, reduced with one part of thinner (4 : 1 : 1), 300 mL needed.
- Sum of parts = 4 + 1 + 1 = 6.
- Base = 300 × 4 / 6 = 200 mL; activator = 300 × 1 / 6 = 50 mL; reducer = 50 mL.
- Pour base to 200, activator to 250, reducer to 300 mL.
200 + 50 + 50 mL. Check the data sheet for the reducer's maximum and for the induction time before spraying.
Limits — when NOT to use this
- The ratio is the product's. Take it from the technical data sheet of the exact product and kit. Ratios differ between products that look alike.
- Pot life. The batch starts its pot life when the parts meet. Mix what you can apply in time.
- Pre-measured kits are meant to be mixed whole. Splitting a kit by eye is how ratios go wrong; split it by weight or volume here.
Questions people actually ask
Is the reducer part of the ratio or a percentage?
Data sheets give it either way. If it is a percentage of the mixed A + B, enter it as parts: 10 % of a 4 : 1 mix is 0.5 parts, so 4 : 1 : 0.5.
My sealant says 10 : 100. Which is A?
Enter the base (the larger part, usually) as A and the accelerator as B: 100 : 10 by weight. Ten grams of accelerator for every 100 grams of base.
Sources
- Arithmetic of proportions, and exact unit factors — 1 US fl oz = 29.5735295625 mL; 1 oz (avoirdupois) = 28.349523125 g; 1 m² × 1 µm = 1 mL. Ratios, pot life and limits are inputs from your product's data sheet.