Soap Calculator
Cold process soap turns oil into soap with lye. This calculator works out how much lye and water one batch needs, using the SAP value of your oil.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Lye needed is the weight of the oil times that oil's SAP value. The SAP value is the grams of lye that fully turn one gram of that oil into soap. Look it up in a published soap-making table for your oil.
Superfat leaves a small share of oil unreacted, so the bar is a little gentler. The percent you enter reduces the lye by that share. Water is a percent of the oil weight.
Lye burns skin and eyes. Wear gloves and eye protection, work in a ventilated room, and always add lye to water, never water to lye.
Worked example
For 32 oz of oil, with 5% superfat and water at 35% of the oil, you need 4.1 oz of lye and 11.2 oz of water.
Questions
Where do I find the SAP value?
Soap-making reference tables list a SAP value for each oil. Use the value for sodium hydroxide, which is the lye used for bar soap.
What superfat should I use?
Many soap makers use about 5 to 8 percent. A higher superfat leaves more oil in the bar and usually makes it milder.
Can I skip the protective gear for a small batch?
No. Raw lye is caustic at any size, so wear gloves and eye protection every time.
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