Saponification
NaOH or KOH needed per oil mass, with batch scaling.
How to use this tool
Work out how much lye to mix with your oils to make soap, with a superfat margin so the bar comes out mild rather than harsh. Pick an oil, enter its weight, and get the lye, water and total batch figures.
What to enter
- Oil / fat: which oil you're saponifying; this sets its SAP value (mg of KOH to saponify 1 g of that oil).
- Oil weight: mass of oil, in grams.
- Lye type: NaOH for a hard bar, KOH for soft or liquid soap.
- Superfat / lye discount: percent of oil left unsaponified for a milder, less-drying bar (typically 5–8%).
- Water: added water as a percent of oil weight (≈33% is common).
Reading the result
You get the lye required, the water to add, and an approximate total batch weight. Heed the caution: lye is caustic, always add lye to water, never the reverse, and wear goggles and gloves. Verify on a second SAP calculator before mixing.
Worked example
500 g of coconut oil with NaOH at a 5% superfat needs about 87 g NaOH and 165 g water (33% of oil weight).
Lye & recipe
The headline lye figure already has your superfat discount applied, it's the exact NaOH or KOH to weigh for this oil and batch, with the water and approximate total below. SAP values are nominal averages, so real oils vary batch to batch: re-check your final recipe on a second calculator and weigh the lye precisely.
Lye from SAP value
Each oil has a saponification value, the mg of KOH to saponify 1 g of that oil. NaOH need = oil(g) × SAPKOH × (40.0/56.1) / 1000. A superfat (lye discount) of 5–8% leaves some oil unsaponified for a milder bar, this tool reduces the lye accordingly. Water is set as a percent of oil weight. Always run your final recipe through a second calculator and work with eye protection: lye is caustic.
Sources
- Published SAP values (KOH mg/g); NaOH/KOH molar masses 40.0 / 56.1 g/mol.