Calculate lye and water for perfect soap
NaOH Needed
76.95
grams
Water
156.23 grams
Total Oils
550.00 grams
Inputs
Result
Total lye = (300 × 0.134) + (150 × 0.178) + (100 × 0.141) = 40.2 + 26.7 + 14.1 = 81.0g. After 5% superfat: 81.0 × 0.95 = 76.95g NaOH. Water = (76.95 / 0.33) - 76.95 = 233.18 - 76.95 = 156.23g.
Inputs
Result
Total lye = (400 × 0.134) + (200 × 0.128) = 53.6 + 25.6 = 79.2g. After 8% superfat: 79.2 × 0.92 = 72.86g. Rounded to 72.86g NaOH. Water = (72.86 / 0.30) - 72.86 = 242.87 - 72.86 = 170.01g. (Values may differ slightly due to rounding at each step.)
Saponification is the chemical reaction between fats/oils and lye (sodium or potassium hydroxide) that produces soap. Each oil has a specific SAP value that determines how much lye is needed.
Superfat (or lye discount) is the percentage of oils that remain unsaponified in the final soap. Typically 5-8%, it makes soap more moisturizing and ensures no excess lye remains.
Sodium hydroxide (NaOH) creates solid bar soap, while potassium hydroxide (KOH) creates liquid soap. KOH requires about 40% more than NaOH for the same amount of oils.
Most soap makers use 28-33% lye concentration. Lower concentrations (more water) give more time to work but longer cure times. Higher concentrations speed up trace and curing.
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Last Updated: Feb 12, 2026
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