Shea Butter Saponification & Lye Calculator

How the lye calculation works

Multiply each oil’s weight by its saponification value, convert to the alkali you are using, then reduce by your superfat percentage. In grams: NaOH = oil g × (SAP ÷ 1000) × (40 ÷ 56.1) × (1 − superfat). KOH = oil g × (SAP ÷ 1000) × (1 − superfat). Superfat is entered as a percentage and converted to a fraction. Water in ratio mode is lye × ratio. Water in concentration mode is lye × (100 − c) / c. Both the ratio and the concentration are shown so the two ways of saying the same thing stay visible.

The NaOH factor 0.128 that soap-makers quote for shea is just SAP 180 expressed as grams of sodium hydroxide per gram of oil: 180 ÷ 1000 × (40.0 ÷ 56.1) ≈ 0.128. Shea’s published identity range is 170–195 mg KOH/g, which corresponds to about 0.121–0.139 g NaOH per g oil. The default of 180 sits in the middle of that literature range. It is not an EMI measured batch value. A batch Certificate of Analysis gives the exact SAP to type into the custom field. The chemistry of the number is on the saponification value page.

Superfat leaves a stated percentage of the oils unsaponified as a safety margin and as conditioning. The allowed range here is 0–15 %, with 5 % as the common bar-soap default. Water at a 2:1 water-to-lye ratio is about 33 % lye concentration.

Assumptions, limits and safety

SAP values are typical published figures. A real lot may differ by several per cent — for exact work use the saponification value from the Certificate of Analysis. The calculator assumes 100 % pure lye. Potassium hydroxide flake is often about 90 % pure; increase the KOH dose by the purity shortfall if your supplier states it. Fragrance, additives, milk and sugars are not modelled, and the tool does not predict trace or cure time.

Unsaponifiables (typically 4–11 % in shea) do not consume lye and are already reflected in the measured SAP — see unsaponifiable matter.

Formulating with shea butter soap

A 100 % shea bar is gentle and conditioning, low-lather, a little soft and slow to cure. Soap makers usually add coconut for lather and palm, kokum or cocoa butter for hardness — see shea butter versus coconut oil and shea versus kokum. A typical shea share in a balanced bar is 15–40 %; higher shares are a marketing “shea bar”.

Grade for soap is usually Grade A or B unrefined. FFA up to about 3 % is tolerated because free fatty acids saponify quickly; higher FFA slightly reduces the superfat margin you need. That is why the FFA titration calculator and the grade checker are useful alongside this calculator, and why shea butter grades and free fatty acid are worth reading before you size a production batch. Do not use this lye calculator for the caustic dose used to neutralise FFA in refining — that is a different calculation; use the caustic soda dose calculator.

EMI Agro does not publish a typical measured SAP for Grade A batches on this page. Use the value on the lot COA in the shea SAP field. Unrefined Grade A supply is described on the Grade A product page. Soap-maker notes are on shea butter for soap makers.