Lye calculator
Enter your oils, superfat and water ratio, and get the exact NaOH and water weights for your cold process batch, with the standard published SAP values.
Your oils
Superfat is capped at 20%.
Water is capped at 100% of the oils.
Superfat leaves a share of the oils unsaponified for a gentler bar: 5% is the common default. Water at 38% of oils is the classic starting point; experienced makers adjust for their process.
Your recipe
Lye per oil
- Olive oil (500 g)64.13 g
- Coconut oil (76°) (300 g)52.15 g
- Palm oil (200 g)26.98 g
Safety first. Lye is caustic: wear gloves and eye protection, add lye to water (never water to lye), and work ventilated. Verify every new recipe with a second lye calculator and run a small test batch before selling. This tool is a starting point, not a substitute for your own checks.
Turn this recipe into a costed batch
Keepsel keeps your soap recipes with real oil prices: every batch you log draws down oils and lye and shows your true cost per bar.
Start free for 30 daysSoap lye math, explained
How much lye do I use per pound of oil?
It depends entirely on the oils: each oil has its own saponification (SAP) value. A pound of olive oil needs about 2.05 oz of NaOH at 5% superfat; coconut oil needs about 2.78 oz. That's why soap recipes are calculated per oil, never with one flat number.
What is superfat and what percentage should I use?
Superfat is the percentage of oils you deliberately leave unsaponified so the bar is gentler and you have a safety margin against lye-heaviness. 5% is the common default; 100% coconut bars often go to 15–20% because coconut cleans so aggressively.
How much water goes into cold process soap?
A classic starting point is 38% of your oil weight, which lands near a 27–28% lye concentration with typical recipes. Less water ('water discount') speeds unmolding and cure but traces faster: a technique to grow into, not start with.
Why do I need to run every recipe through a lye calculator?
Because oils vary and arithmetic mistakes in soap are safety problems, not typos. Too much lye makes a caustic bar. Calculate every new recipe, verify it with a second calculator, and confirm with a small test batch before selling: every experienced soap maker does all three.
Can I swap one oil for another without recalculating?
No. SAP values differ oil to oil (olive 0.135 vs coconut 0.183 NaOH), so swapping even a few hundred grams changes the lye your recipe needs. Any substitution means a fresh calculation.
Also useful: the free soap pricing calculator for what each bar costs and earns. And see how Keepsel runs a whole soap business.
From recipe to costed batches
Keepsel keeps your soap recipes with real oil prices: log a batch and your oils and lye draw down, and every bar knows its true cost.
Start free for 30 days