Free Soap Calculator & Lye Calculator
New to soap making? Read our guide below
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What is a Soap Calculator?
A soap calculator (also called a soap recipe calculator or soap making calculator), also known as a lye calculator, is an essential tool for anyone making handmade soap. Whether you are crafting cold process, hot process, or liquid soap, this calculator determines the precise amount of lye needed to safely convert your oils into soap through a chemical reaction called saponification.
Every oil and fat has a unique SAP value (saponification value), which represents the amount of lye required to fully convert it to soap. This calculator uses these values along with your chosen superfat percentage to help you formulate balanced, skin-friendly recipes.
If you are new to soap making, do not worry. The calculator guides you through each step, and the results update automatically as you adjust your recipe.
How to Use This Free Lye Calculator
- Choose your soap type: Select solid soap (NaOH), liquid soap (KOH), or a hybrid formulation that uses both lyes
- Select your units: Work in grams, ounces, pounds, or percentages
- Set your water ratio: Choose lye concentration or water-to-lye ratio
- Set your superfat level: Typically 3% to 8% for moisturizing soap with a safety margin
- Select your oils: Choose from our database of oils, fats, and butters with accurate SAP values
- Add fragrances and additives: Calculate fragrance load and track colorants or other ingredients
- Save your recipe: Create an account to save your recipes and access them from any device
Soap Calculator Features
- Easy recipe builder with real-time calculations as you adjust ingredients
- Save and organize recipes with your account (unlimited with premium)
- Cold process and hot process soap calculations
- Liquid soap support using potassium hydroxide (KOH)
- Mold size calculator to resize recipes for your soap molds
- Recipe scaling to adjust batch sizes up or down
- Large oil database with accurate, maintained SAP values
- Master batch lye calculations for experienced soap makers
- Mobile apps available for iOS and Android
Soap Molds and Batch Sizing
Choosing the right soap molds and batch size is easier with our built-in mold calculator. Enter your mold dimensions (length, width, height) or total volume, and the tool will tell you how much soap batter you need. Whether you use loaf molds, slab molds, or individual cavity molds, you can scale any recipe to fit. After building your recipe above, use the mold section to resize for your soap molds.
Looking for ideas? Browse our soap recipes and use this calculator to adapt them to your molds and batch size.
Frequently Asked Questions
What is a soap calculator?
A soap calculator is a tool that helps soap makers determine the exact amount of lye (sodium hydroxide for bar soap or potassium hydroxide for liquid soap) needed to saponify a specific combination of oils and fats. It calculates precise ratios to help you create soap that is safe to use.
Why do I need a lye calculator for soap making?
Each oil has a unique SAP (saponification) value, which is the amount of lye needed to turn it into soap. Using too much lye creates harsh, caustic soap. Too little leaves unreacted oils. A lye calculator handles these calculations automatically, accounting for superfat percentages and water ratios.
What is superfat in soap making?
Superfat, also called lye discount, is the percentage of oils left unsaponified in your finished soap. A 5% superfat means 5% of your oils remain as free oils, which can make the soap more moisturizing and helps ensure no excess lye remains. Most soap makers use between 3% and 8% superfat.
What is the difference between NaOH and KOH in soap making?
NaOH (sodium hydroxide) is used to make solid bar soaps through cold process or hot process methods. KOH (potassium hydroxide) is used to make liquid soaps and soft soaps. Some recipes use both lyes together, which is known as a hybrid formulation.
How do I calculate water for cold process soap?
Water is typically calculated as a ratio to lye (such as 2:1 water to lye) or as a percentage of your total oil weight (typically 33% to 38%). This calculator lets you choose your preferred method and adjust for your climate and recipe needs.
Is this soap calculator free to use?
Yes, the soap calculator is completely free to use. Create a free account to save up to 2 recipes and track batches. Premium members get unlimited recipe storage and an ad-free experience.
