SAP Value Chart for Soap Making: What SAP Value Means

Classic lab SAP is milligrams of potassium hydroxide to saponify one gram of fat. Soap calculators store the practical form: grams of NaOH per gram of oil. A KOH SAP is the same relationship expressed for potassium hydroxide.

The number moves because fats are not one molecule. Coconut is rich in shorter chains. Olive is mostly oleic. Tallow sits in between, and its SAP moves with the animal and the trim. A published chart is an average of a defined crop or render, not a universal constant.

Use the figure that matches the alkali in the cup. A NaOH SAP fed into a KOH batch is a lye-light error. The reverse is lye-heavy.

Take coconut oil (76°) as the single fat. Its NaOH SAP on the Saponis oil sheet is 0.183 g of NaOH per gram of oil.

• 100 g of that oil, at zero superfat, calls for 18.3 g of NaOH.
• A 5% superfat withholds 5% of that alkali: 18.3 × 0.95 = 17.385 g of NaOH.

The oil weight does not change. Only the alkali does. Add a second oil and you do not average the SAP values by vibe. You multiply each oil's weight by its own SAP, sum the lye, then apply superfat once.

That is the whole chart. Rows are oils. Columns are discounts. A blend is a sum down the column, not a new SAP invented for the recipe.

Eyeballing is how lye-heavy soap happens. "About the same as last time" fails when the olive percentage moved, the coconut was a different grade, or the batch was scaled to a new mold and the water was scaled but the lye was copied.

A stale chart fails more quietly. SAP tables in old books disagree with each other in the third decimal. That digit is tenths of a gram on a small batch and grams on a production slab. Enough to zap. Enough to soften.

A calculator is the chart kept current: one verified SAP per fat, NaOH and KOH both available, superfat applied after the sum. It also refuses the silent error of a 100% sum that is actually 98% because of a typed weight.

SAP does not tell you hardness, lather, or a recommended maximum. Those come from the fatty-acid split — lauric, myristic, palmitic, stearic, oleic, and the rest — and from practice. An oil can have a modest SAP and still be a poor idea at 40% of the blend.

SAP does not include the superfat. If you look up a chart value and weigh that lye, you have chosen 0% superfat whether you meant to or not.

SAP does not know your water. Water is a solvent and a temperature sink. It is not part of the saponification ratio. Discount water for a harder pour. Do not discount lye to make the batch thicker.

Build the formula as weights of fats. Confirm the weights sum to the oil phase you intend. Read each SAP. Multiply. Sum. Apply one superfat. Round the lye to the precision of the scale — 0.1 g is the useful floor on a home batch under a kilogram.

Then stop editing. Changing an oil after the lye is weighed is how the SAP work gets thrown out.

Check a single-oil example against the library before you trust a new tool. The Saponis soap bench (/soap) stores a verified SAP for each of 22 fats and butters, and runs NaOH, KOH, or a dual-lye blend from those figures.

If the hand product and the calculator disagree, believe neither until you find the rounding. The scale will not arbitrate a math error.