Soap Recipe Calculator
Quick lye math in your browser — no sign-in, and recipes aren't saved or synced with the app.
Recipe
Your Recipe
Soap Properties
Fatty Acid Profile
About this soap lye calculator
Simple SoapCalc's free soap lye calculator works out exactly how much lye — sodium hydroxide (NaOH) for bar soap or potassium hydroxide (KOH) for liquid soap — and how much water your recipe needs, based on the saponification (SAP) values of the oils you choose. Enter oils by percentage or weight, set your superfat and water, and it instantly shows the lye and water amounts plus the soap's estimated qualities: hardness, cleansing, conditioning, bubbly and creamy lather, and longevity. It supports 150 oils, butters and fats, works in grams or ounces, and prints a recipe sheet.
How to use it
- Add your oils — by percentage, or switch to Weight to enter exact amounts.
- Using percentages? Set your batch size and check that the total reads 100%.
- Choose your lye and water, or keep the defaults.
- Read your lye and water in Your Recipe.
- That's it — you're done! Print a recipe sheet whenever you're ready.
Frequently asked questions
What is a soap lye calculator?
A soap lye calculator works out the exact amount of lye and water your recipe needs to safely turn oils into soap, using each oil's saponification (SAP) value. Making soap without running the recipe through a lye calculator risks a caustic, lye-heavy bar.
NaOH or KOH — which lye should I use?
Sodium hydroxide (NaOH) makes solid bar soap; potassium hydroxide (KOH) makes liquid or soft cream soap. This calculator supports NaOH, KOH, or a hybrid blend of both.
What is superfat?
Superfat is the percentage of oils left unsaponified so the finished soap is more moisturizing and never lye-heavy. Around 5% is a common starting point.
What is the difference between water:lye ratio, lye concentration, and water as a percent of oils?
They are three ways to express the same thing — how much water dissolves your lye. A 2:1 water:lye ratio is about 33% lye concentration. Switch methods in the calculator and the numbers convert automatically.
What do the soap qualities mean?
Hardness, cleansing, conditioning, bubbly and creamy lather, and longevity are estimates from your oils' fatty-acid profile. They are guidance, not pass-or-fail targets — every soap is a balance.
What are the default settings?
The calculator opens with common starting points you can keep or change: 5% superfat, a 2:1 water:lye ratio, and NaOH (for solid bar soap), at a 1000-gram batch. These are typical defaults many soapmakers begin from — adjust them to suit your oils and process.
What lye purity does this calculator assume?
It uses the standard soapmaking values — 100% NaOH and 90% KOH. In practice NaOH is usually sold at 97–100% and KOH around 90%, so if your lye's purity is different, your numbers change slightly. The Simple SoapCalc app lets you set exact purity to match your label.
Can I work in ounces or grams?
Both. Toggle g or oz next to Total oils and every amount converts.
Is the calculator free? Do I need an account?
Yes, it is completely free with no sign-up.
Is this the same as the Simple SoapCalc app? Are my recipes linked?
The web calculator is a free standalone tool for quick lye math — no account, and it does not sync with the app. Recipes you enter here are not saved to an app account, and app recipes do not appear here. The Simple SoapCalc app for iOS and Android is a separate, fuller product that saves recipes, syncs across your devices, troubleshoots batches, and helps you build and adjust recipes.
Did the creators approve their recipes being here?
Yes — recipes from other soapmakers are featured with credit and a link to their website, where you'll find the complete recipe (fragrance, colorant, liquid, and full method). The unattributed starter recipes are classic, widely-used formulas.
Safety: Always run your recipe through a lye calculator before making soap, wear gloves and eye protection, and add lye to water — never water to lye. Values here are estimates; double-check critical batches against a second source.
This free web tool covers lye, water, and soap qualities. The Simple SoapCalc app adds recipe saving & sync, photo and paste import, hands-on recipe tuning with Tweaker, batch troubleshooting, and predictions for trace, cure, and more.
