The Soap Bench is a free calculator for handmade soap. You pick your oils, set a superfat and a water amount, and it tells you exactly how much sodium hydroxide or potassium hydroxide to weigh. It covers cold process and hot process bars, liquid soap, and dual-lye recipes such as cream and shave soaps.
The point of a tool like this is cheap experimentation. You can try a dozen oil combinations on screen, watch the hardness, cleansing, conditioning, and lather numbers move, and only buy oils for the recipe you actually like.
Every oil has a published saponification value, the amount of lye needed to turn one gram of that oil into soap. The Soap Bench multiplies each oil's weight by its value, adds them up, and then holds back your superfat percentage as a safety margin. Water comes from your chosen method: lye concentration, water to lye ratio, or percent of oils. Potassium hydroxide amounts are corrected for purity, since commercial KOH is usually about 90% pure.
The database covers 144 oils, butters, and waxes. The saponification values, fatty acid profiles, iodine, and INS numbers are the same published figures the soap-making community has used for years, and every value was cross-checked against a second independent source before it shipped. Displayed lye weights always round down, never up, so rounding can only add to your safety margin.
The calculator is free and works without an account. Signing in with an email code lets you keep your recipes across devices. The site shows one quiet ad to help cover hosting. That is the whole business model.
The Soap Bench is a one-person project, built after a soap calculator I relied on stopped working. Questions, corrections, and requests for missing oils are welcome on the contact page.
See also: privacy. Lye safety notes live at the bottom of the calculator.