Soap Lye Calculator

Enter each oil name, weight, and independently verified SAP value, then select NaOH or KOH. The calculator applies superfat, product purity, and either lye concentration or water-to-alkali ratio.

Inputs

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Result

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Oil rows calculated: 1
Total oil mass: 500 g
Oil percentages by weight: Olive oil example — verify supplier SAP: 100.00%
Pure alkali demand by oil row: Olive oil example — verify supplier SAP: 67.00 g
Selected alkali: NaOH
Pure NaOH at zero superfat: 67 g
Pure NaOH after superfat discount: 63.65 g
NaOH product at entered purity: 63.65 g
Water under the selected method: 129.23 g
Resulting lye concentration: 33 %

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How to use the Soap Lye Calculator

Enter matching oil names, weights, and verified SAP values, alkali type, superfat, purity, and water method.

Review supplier NaOH SAP values, NaOH purity, measurement accuracy, additives, process method, personal protective equipment, and safe handling procedure.

Read oil percentages, per-oil alkali demand, selected alkali, pure and product alkali mass, water mass, and resulting concentration.

Formula

Pure alkali = Σ(oil weight × matching NaOH or KOH SAP) × (1 − superfat). Product mass = pure alkali ÷ purity; water follows entered lye concentration or water-to-alkali ratio.

Example

For 500 g of an oil with NaOH SAP 0.135, theoretical NaOH is 67.5 g; 5% superfat reduces the modeled amount to 64.125 g before purity adjustment.

Assumptions and limitations

NaOH and KOH are strongly corrosive. All SAP values are user-supplied and must be independently verified; this arithmetic is not a handling, mixing, recipe, or finished-soap safety procedure.
Soap Lye Calculator treats the entered values as estimates and does not infer missing project, account, or personal details.
Calculations retain working precision except where the cited method requires an intermediate rounding step; displayed values are then formatted separately. Source rules and dated rates must be rechecked when they change.

Sources

Centers for Disease Control and Prevention: Sodium Hydroxide: NIOSH Pocket GuideSodium hydroxide hazards and exposure precautions. Reviewed 2026-08-14.
National Institute of Standards and Technology: SI Units — LengthLength, area, volume, and unit-conversion conventions. Reviewed 2026-08-14.
National Institute for Occupational Safety and Health: NIOSH Pocket Guide to Chemical Hazards — Potassium HydroxideOfficial formula, rate, or program guidance used by this calculator. Reviewed 2026-08-14.

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Frequently asked questions

How does the Soap Lye Calculator work?

Pure alkali = Σ(oil weight × matching NaOH or KOH SAP) × (1 − superfat). Product mass = pure alkali ÷ purity; water follows entered lye concentration or water-to-alkali ratio.

What information should I enter in the Soap Lye Calculator?

Enter matching oil names, weights, and verified SAP values, alkali type, superfat, purity, and water method, then verify supplier NaOH SAP values, NaOH purity, measurement accuracy, additives, process method, personal protective equipment, and safe handling procedure.

What should I verify before using this Soap Lye Calculator result?

NaOH and KOH are strongly corrosive. All SAP values are user-supplied and must be independently verified; this arithmetic is not a handling, mixing, recipe, or finished-soap safety procedure.

Reviewed 2026-08-14 · oil-rows-alkali-water-2.0.0 · content-2026-08-14 · Trusty Calculator Editorial Team