Lye Calculator

This works out the lye and water for a cold or hot process soap batch from up to three oils. For each oil you give the weight and its saponification value in milligrams of KOH per gram, then choose sodium or potassium hydroxide, a superfat percentage and how the water is set, either as a lye concentration or as a share of the oil weight. The saponification value is an input rather than a stored table because it is measured on a particular batch of oil and published figures for the same oil differ by two to four percent, which is more than a small superfat; take it from your supplier spec sheet. The sodium hydroxide figure is derived from the potassium one by the molar mass ratio 40.00 to 56.1056, so the two stay consistent. Nothing here proves a bar is safe: lye burns skin, and the cured batch still has to be tested before use.