Soap Lye Calculator

How to use this calculator

Follow these steps to build and review a recipe.

1. Choose your lye. Pick NaOH (bars/bast) or KOH (liquids). If you select KOH, set the purity so the tool adjusts the lye weight automatically.
2. Set your batch size. Select the working unit (lb, oz, g) and enter total oil weight. Use the optional bar calculator to back into a target bar count + weight; the “Weight of oils” field auto-updates when both are filled.
3. Dial in water & tweaks. Keep “Water % of oils” or switch to lye concentration / water:lye ratio. Adjust superfat and, if needed, the fragrance helper to see oil-weight-based fragrance amounts in your selected mode.
4. Add oils from the library. Search/browse to add an oil, then set its percentage (or switch to the weight columns). The totals badge tells you when you’ve hit 100%; if not, the tool normalizes during calculations. Drag handles let you reorder.
5. Review results instantly. Required lye + water, per-oil weights, fatty-acid profile, and derived soap qualities update with every change. The “Sat : Unsat” ratio and fragrance output surface as soon as the relevant fields are set.
6. Bonus helpers. The oil library modal shows fatty acids, INS, and SAP for each oil. Notes save with your recipe. Undo removes the last oil delete. A QR code and shareable URL let you reopen the exact recipe elsewhere.
7. Save, print, export. Use the actions panel to save/load recipes (stored locally), copy the URL, print with optional sections, or download oil-weight + metrics CSV files.