Soap Superfat Percentage Calculator

Work out soap superfat percentage instantly with clear inputs, formula shown and shareable results.

About Soap Superfat Percentage Calculator

Superfatting reduces the alkali below the amount needed for complete saponification, leaving free oil in the bar for conditioning and providing a safety margin against measurement error. Five percent is standard; 1-2% suits laundry and 8-15% suits facial and shaving bars. Lye concentration of 28-33% is typical.

Formulas

Superfat

Alkali = alkali at zero superfat x (1 - superfat %)

Lye concentration

Concentration % = alkali x 100 / (alkali + water)

Worked example

With the default values below, Soap Superfat Percentage Calculator returns Alkali Required of 180.500. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total Oil Massminimum 0 g: 1,000 g
Alkali For Full Saponificationminimum 0 g: 190 g
Superfataccepts 0–30 %: 5 %
Water As Percentage Of Oilsaccepts 0–100 %: 33 %

Results

Alkali Required: 180.500
Water Required: 330.000
Lye Solution Concentration: 35.357%
Unsaponified Oil In The Bar: 50.000

Step by step

1Values used
2Superfat
3Lye concentration
4Alkali Required= 180.500
5Water Required= 330.000
6Lye Solution Concentration= 35.357
7Unsaponified Oil In The Bar= 50.000

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Soapmaking uses corrosive alkali and generates heat. Wear eye and skin protection, and cure and test the final pH before use or sale.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Soapmaking uses corrosive alkali and generates heat. Wear eye and skin protection, and cure and test the final pH before use or sale.

Frequently Asked Questions

Why is superfat a safety margin?

It guarantees the bar cannot be lye-heavy even with small weighing errors or an imprecise SAP value. A zero-superfat recipe with a 2% error becomes caustic and unusable.

What does water discount do?

Less water gives a firmer bar sooner and faster unmoulding, but a hotter, faster reaction with more risk of cracking and overheating. High water gives more working time and a softer initial bar.