Sizu Home › Calculators › Lye Water and Strength
Opens on the book's Market Batch. Change any number to your own and press Calculate.
Enter the lye and press Calculate.
The formula
- From a concentration: water = lye × (1 − c) ÷ c
- From a ratio: water = lye × ratio. Ratio = (1 − c) ÷ c; c = 1 ÷ (1 + ratio)
- From % of oils: water = oils × % ÷ 100 (the strength then depends on the recipe)
- Heat as it dissolves = lye ÷ 39.997 g/mol × 44.51 kJ/mol, about 1.11 kJ per g
The book's worked example, Chapter 4. The Market Batch's 132.6 g of NaOH at 33 %: 132.6 × 0.67 ÷ 0.33 = 269.2 g of water, a ratio of 2.03 : 1 and 28.04 % of the oils; 401.8 g of solution, releasing about 148 kJ as it dissolves.
Lye into water, slowly, stirring, never water onto lye: it gets hot enough to scald. Distilled water. 33 % is the all-round setting; about 28 % for a coconut-heavy bar, up to 40 % for a slow olive recipe. Prices are illustrative US supplier prices from October 2026, shown without a currency sign; put in your own. Everything stays in your browser: no sign-up, nothing stored.