Soap Lye Calculator

Summary

Calculate the exact amount of NaOH or KOH lye needed for soap making based on your oil blend and desired superfat.

How it works

1. Select NaOH (for bar soap) or KOH (for liquid soap) as your lye type.
2. Add each oil to your recipe using the oil selector and enter its weight in grams or ounces.
3. Set a superfat percentage (2–10% is typical) to leave a small amount of free oil that does not react with lye.
4. The calculator multiplies each oil weight by its SAP value, sums the results, and reduces by the superfat percentage to get the lye amount.
5. Water amount is calculated as a ratio of the total oil weight (standard 33% lye concentration).
6. Review the summary and use the copy button to paste results into your notes.

Use cases

• Plan a cold process bar soap batch with a custom oil blend.
• Formulate liquid castile or potassium soap using KOH.
• Adjust superfat level to create a more moisturizing bar.
• Scale an existing recipe up or down by weight.
• Verify a handwritten soap recipe before committing to a batch.
• Teach beginner soap makers the saponification concept interactively.

Frequently Asked Questions