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The lye calculator that shows its work.

NaOH, KOH or dual lye. Water three ways at once. Citric acid and milk handled with real chemistry. Mold sizing that respects your recipe. And beside every number, the formula, the substitution and the source.

Open the calculator Browse the oils

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Every formula cited
Every oil value sourced

Specimen · computed at build time

60 % olive oil (virgin / refined / olive oil), 25 % coconut oil, 10 % shea butter, 5 % castor oil · 1000 g oils · 5 % superfat · 33 % lye solution

Sodium hydroxide138.9 g
Water282.0 g 2.03 : 1
Hardness · cleansing · conditioning35 · 17 · 61
Iodine · INS62 · 143

Every oil value above has a published range and a named source. Open the recipe and the explain drawer shows each step.

Open this recipe

Exact

The saponification arithmetic every calculator shares, with the constants cited. Oil values kept as the published range, not one copied number.

Explained

Every result opens to its formula and substitution. Water is shown as a concentration, a percentage of oils and a ratio, because they are one quantity.

Yours

Permalinks now; saved recipes, versions and batches next. Import and export in open formats, free, forever. The data is ODbL and the formulas are MIT.

Calculators

Lye calculator NaOH, KOH or dual lye, water three ways, additives, fragrance, mold sizing — every number explained

Import a recipe Paste from another calculator, a spreadsheet or a forum post and see exactly what was read

Liquid soap dilution Water to add to a potassium soap paste for the concentration you want

Fragrance & allergen check IFRA load by product type and EU/Canada allergen declarations from supplier sheets

Reference

Oil & butter reference Saponification values, iodine, fatty acids — as published ranges with the source on every row

Formulas & sources The exact equations behind every result, with citations

Workbench

Recipes, versions & batchessoon Save recipes, track batches and cure, compare versions

Why another soap calculator

Every soap calculator ships the same unattributed oil table, and nobody can say where a single number in it came from. The one people trust most cannot save a recipe, went offline for months in 2025, and shipped wrong oil data when it came back. The ones that can save recipes carry years-old bugs in mold sizing and resizing.

This one starts from the other end: 99 ingredient records transcribed from 47 primary publishers with the document named on every row, a formula library with a citation on every constant, and an explanation beside every number. The calculator is free and stays free. The workbench that grows around it is what we will charge for.

Know when the workbench lands

Saved recipes, versions and a batch log are what comes next. Leave an address and you will hear when they are ready, plus a short note whenever something ships. No newsletter, nothing sold, one click to stop.