Lye calculator
Enter your oils, superfat and water ratio — get the exact NaOH and water weights for your cold process batch, with the standard published SAP values.
Your oils
Superfat (%)
Water (% of 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
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
Hivara stores your soap recipes with real oil prices — every batch you log draws down oils and lye and shows your true cost per bar, cure dates included.
Start freeSoap 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 Hivara runs a whole soap business, cure times and lot tracking included.
From recipe to costed, cured batches
Hivara keeps your soap recipes with real oil prices — log a batch and your oils draw down, bars go on the cure rack with a date, and every bar knows its true cost.
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