Lye Soap Calculator

Soap type

Unit of measurement

Oil Ingredients

Superfat / lye discount (%)

Lye concentration (%)

NaOH purity (%)

Most store-bought lye is ~97% pure (NaOH) or ~90% pure (KOH). Adjust if your label says otherwise.

Resize to total oil weight (optional)

Leave blank to use the oil weights entered above as-is.

Total oil weight-

Sodium hydroxide (NaOH)-

Water-

Total batch weight-

Always add lye to water, never water to lye. Wear gloves and eye protection. Double-check figures before making a batch — this tool is a starting point, not a substitute for careful practice.