What this tool does
Pick your oils, and this calculator figures out how much lye and water you need. It also gives you a heads-up about how your soap might turn out - hard or soft, bubbly or creamy, cleansing or gentle.
Whether it's your first batch or your fiftieth, the goal is simple: take the guesswork out of recipe building.
How it figures out lye amounts
Every oil needs a specific amount of lye to turn into soap. Olive oil needs a different amount than coconut oil, which needs a different amount than shea butter. These numbers (called SAP values) have been worked out by chemists and are the same everywhere.
The calculator just adds up how much lye each oil in your recipe needs, then subtracts a bit for your superfat. That's it.
How it predicts soap qualities
Different oils make different kinds of soap. Coconut oil makes hard, bubbly, cleansing soap. Olive oil makes softer, gentler, creamier soap. The calculator looks at what's in your oils and predicts what your soap will be like:
- Hardness - will the bar hold up or turn mushy?
- Cleansing - how strong is the cleaning power?
- Conditioning - how gentle is it on skin?
- Lather - big fluffy bubbles or dense creamy lather?
The predictions aren't perfect - your technique, cure time, and water all matter too. But they give you a reasonable idea of what to expect.
About the recommended ranges
You'll see suggested ranges for each quality (like hardness 29-54). These aren't from scientific studies - they're from soapmakers sharing what works. The ranges come from SoapCalc, which has been helping soapmakers for years.
Think of them as a starting point, not rules. Plenty of lovely soaps fall outside these ranges. If your recipe works for you, the numbers don't matter.
Where the information comes from
The oil data (SAP values, what's in each oil) comes from chemistry databases and food science sources - the same places labs and manufacturers use.
The suggested ranges and tips come from the soapmaking community, especially Kevin Dunn's book Scientific Soapmaking and the collected wisdom of forums and groups.
You can see everything on the references page.
A note on the INS value
You might see an "INS" number with a suggested range of 136-165. Honestly? It's controversial. Some soapmakers swear by it, others ignore it completely. Many wonderful soaps fall outside the "ideal" range. Use it if you find it helpful, skip it if you don't.
Your privacy
Everything happens on your computer. Your recipes are saved in your browser and never sent anywhere. There's no account to create, no data collected, no tracking.