Lyestone: Soap Batch Planner

If you make soap from scratch, you already know the one number you cannot guess: how much lye a given blend of fats needs to saponify cleanly. Lyestone is a lye calculator for exactly that. Choose your oils, enter the grams, set a superfat and water amount, and it works out the sodium hydroxide for bar soap or the potassium hydroxide for liquid soap. The same recipe, either lye, without redoing the math.

It ships with a library of common saponifiable fats and their SAP values for both NaOH and KOH, so you are not copying figures off a website in another tab. Alongside the lye weight it shows the qualities soap makers actually judge a recipe by, including hardness, cleansing, conditioning, and lather, each with a target band, plus iodine and INS values and plain warnings when a blend is likely to dry the skin.

For people who batch at scale there is a lye-concentration mode, fragrance and salt figures, and a one-tap share to drop a recipe into your notes. It runs the same on a phone and on an iPad propped up on the workbench.

Lyestone works entirely offline and is a single $0.99 purchase, with no account, no ads, and no subscription. Lye is caustic, and the app is a hobbyist reference rather than a substitute for gloves, goggles, and careful practice.