Superfat Calculator
See how superfat changes your lye: enter the full lye amount and a superfat percent to get the reduced lye to use and the grams of oil left unsaponified. Calculates in your browser.
Lye to use
-
Show the math
Superfat leaves a share of your oils unsaponified for a milder, more moisturising bar by using a little less lye than a full reaction would need:
lye to use = full lye × (1 − superfat ÷ 100)
lye discounted = full lye × superfat ÷ 100
Higher superfat means gentler soap but a softer bar and a shorter shelf life before the extra oils can go rancid. Always confirm your full lye figure with a trusted calculator. Too little lye leaves soap oily, too much makes it harsh and unsafe.
What this does
A superfat calculator shows how superfat changes your lye: enter the full lye amount and a superfat percent to get the reduced lye and the oil left unsaponified.
How to use it
- Enter the full lye amount.
- Set your superfat percentage.
- Read the reduced lye to use.
- See the discounted grams.
How it works
Superfat leaves a share of oils unsaponified for a milder bar. Most bar soaps use 5–8%; more is gentler but softens the bar and shortens shelf life.
lye to use = full lye × (1 − superfat ÷ 100)
Understanding your result
Superfat is the share of oils left unsaponified to make a milder, more moisturising bar, and 5 to 8 percent suits most recipes. Pushing it higher feels gentler but softens the bar, shortens shelf life, and can speed up rancidity, so treat the reduced lye figure as a balance between skin-feel and a hard, long-lasting bar rather than a maximise-it dial.
Example
At 5% superfat, 70 g of full lye drops to 66.5 g.
Sources & methodology
Last updated .
Frequently asked questions
What is superfat?
Superfat is the share of oils left unsaponified for a milder, more moisturising bar. It works by using slightly less lye than a full reaction would consume.
How much superfat should I use?
Most bar soaps use 5–8%; facial bars and salt bars often go higher. More superfat is gentler but softens the bar and shortens shelf life.
How is the lye discount found?
Lye to use = full lye × (1 − superfat ÷ 100), and the discounted grams are full lye × superfat ÷ 100.
Is anything saved?
No — it all runs locally in your browser.
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