Soap Lye Calculator
Enter your oil blend and superfat percentage to get exact sodium hydroxide (NaOH), water, total batch weight and lye concentration for cold process soap. Everything runs locally in your browser β your recipe never leaves your device.
β Oil blend
β‘ Settings
Water:Lye = 2 means water weight is twice the lye weight (β33% lye concentration). Higher ratio = slower trace & longer cure; lower = faster. Common range 1.5β3.
β’ Results
Frequently asked questions
What is SAP and why use it for lye?
The saponification value (SAP) is the milligrams of KOH needed to saponify 1 gram of a given oil. Converting to NaOH gives the grams of sodium hydroxide required. Oils differ a lot (coconut β0.190, olive β0.134), so each oil must be calculated separately and summed β a single average ratio will be inaccurate.
What is superfat and why 5% by default?
Superfat means deliberately using less lye so a small amount of oil stays unsaponified, leaving a milder, more moisturizing bar. We multiply total lye by (1 β superfat%). Home soapmakers commonly use 5%β8%; facial bars 2%β3%. Above 10% the bar risks rancidity and DOS (dreaded orange spots).
How do I choose the water:lye ratio?
Water only affects the speed and hardness of the process, not the final fatty-acid composition. More water = lower lye concentration = slower trace and longer cure; less water = faster setup and less working time. The classic ratio is 2:1 (β33% lye concentration). Hot-process or quick-unmold batches can use less.
How accurate are the results?
This tool uses widely accepted NaOH saponification coefficients, accurate for the vast majority of oils. Unrefined or blended oils may vary slightly, so test a small batch the first time you use a new recipe. Results are for guidance and not a commercial formulation guarantee.