GlenCalc

Soap lye calculator

One oil per line with its weight in grams, using the names below. Lye is caustic: wear goggles and gloves, and add lye to water, never water to lye.

Names: olive, coconut, palm, castor, shea, cocoa, sunflower, almond, avocado, lard, tallow, canola.

Your answer

Sodium hydroxide140.6 g
Water281 g
Total oils1,000 g
Batch weight1,422 g
  • SAP values vary between batches of oil; this uses typical values. Check your recipe in a second lye calculator before making soap.

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How we worked it out

Updated as you change the numbers.

  1. Lye = Σ (oil weight × its SAP value) × (1 − superfat). Water = lye × the water ratio.

Method and assumptions

Each oil needs a set amount of lye to turn into soap (its saponification value). A superfat of about 5% leaves some oil unsaponified for a milder bar and a safety margin. Potassium hydroxide is about 1.4 times the weight of sodium hydroxide for the same oils, and is usually sold 90% pure.

Questions

How much lye for 500 g olive, 300 g coconut, 150 g shea and 50 g castor oil?

About 140.6 g of sodium hydroxide at 5% superfat, with 281 g of water.

Sources

Method and figures checked on . Every worked answer on this page is covered by an automated test. Found a mistake? Tell us.

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