Soap Lye Calculators

Free tools for cold-process soap makers — exact lye and water amounts for your recipe, ratio/concentration conversions, and a sourced oil reference chart.

Safety first: lye (sodium or potassium hydroxide) is caustic. Always add lye to water, never water to lye, never use aluminum containers or utensils (lye reacts with aluminum to release flammable hydrogen gas), and wear sealed goggles and gloves. See the lye calculator for the full safety notes, including first aid.

Lye calculator

Enter your recipe's oils and superfat — get the exact NaOH or KOH and water amounts.

Water:lye ratio converter

Convert between water:lye ratio, lye concentration %, and water weight for a known lye amount.

Oil SAP value reference chart

Sourced saponification values for common soap-making oils and fats, NaOH and KOH.