Cold Process Soap Lye Calculator
Calculate the exact amount of NaOH lye and water needed for cold-process soapmaking based on oil type, weight, and desired superfat percentage.
Results
What is it?
The cold process soap lye calculator determines how much sodium hydroxide (NaOH) and water you need to saponify a given weight of oils. Saponification is the chemical reaction between lye and fat that creates soap and glycerin.
How to use
Enter your total oil weight, select the primary oil type (each oil has a unique SAP value), choose your superfat/lye discount percentage (how much extra oil to leave unsaponified for skin feel), and set your water ratio. The calculator outputs precise gram measurements for your lye and water.
Example scenario
For a 500 g olive oil soap with 5% superfat and 38% water: NaOH needed � 63.6 g, water � 190 g, giving a 25% lye solution. This is a classic Castile soap formula.
Pro tip
?? WARNING: NaOH is highly caustic. ALWAYS add lye crystals slowly to water � never water to lye (this can cause violent boiling). Wear safety goggles, rubber gloves, and work in a ventilated area. The mixture will heat to ~85�C.