Lye Calculator

Overview

The Lye Calculator is Formuley's most popular calculator, purpose-built for soap makers. It calculates the precise amount of lye (sodium hydroxide or potassium hydroxide) and water needed to saponify your chosen oils and butters. It also predicts the qualities of your finished soap so you can adjust your recipe before making a batch.

Getting Started

1. Open the sidebar and navigate to Tools / Calculators.
2. Select Lye Calculator.

Entering Your Oils and Butters

The first step is building your oil blend:

1. Click Add Oil to add an oil or butter to your recipe.
2. Select an ingredient from your ingredient library. Formuley auto-populates the SAP (saponification) value for each oil, so you do not need to look up these values manually.
3. Enter the weight or percentage for each oil. If you enter weights, the calculator derives percentages automatically, and vice versa.
4. Repeat for each oil in your recipe. You can add as many oils as you need.

To remove an oil, click the delete button next to its row.

Choosing Your Lye Type

Select the type of lye for your soap:

• NaOH (Sodium Hydroxide) -- used for bar soap. This is the most common choice.
• KOH (Potassium Hydroxide) -- used for liquid soap and cream soap.
• Dual Lye -- a blend of NaOH and KOH. When you select this option, an additional field appears where you set the NaOH-to-KOH ratio.

The calculator adjusts the SAP values and lye amounts based on your selection, since NaOH and KOH have different molecular weights and saponification requirements.

Setting Superfat Percentage

The Superfat % field controls how much of your oils remain unsaponified in the finished soap. A higher superfat means more moisturizing oils are left in the bar.

• 5% is a common starting point for most recipes.
• 5-8% is the typical range for skin-friendly bar soap.
• Higher superfat values (8-10%+) create a more conditioning bar but may reduce lather and shelf stability.

Configuring the Water Amount

You can set your water amount using one of two methods:

• Water:Lye Ratio -- specify the ratio of water to lye (for example, 2:1 means twice as much water as lye by weight). A lower ratio produces a harder bar that unmolds faster.
• Water as % of Oils -- set water as a percentage of your total oil weight. This method is sometimes preferred for consistency across different recipe sizes.

Reading Your Results

After entering all inputs, click Calculate. The results section displays:

• Total Lye Needed -- the total weight of NaOH, KOH, or both (in grams).
• Total Water Needed -- the weight of water (in grams).
• Per-Oil Lye Breakdown -- a table showing how much lye each individual oil requires, which helps you understand the contribution of each oil to the overall recipe.

Predicted Soap Qualities

Below the lye calculations, the calculator displays predicted qualities for your finished soap based on the fatty acid profile of your oil blend:

• Hardness -- how firm the bar will be.
• Cleansing -- the degree of cleansing action (higher values may be more stripping).
• Conditioning -- how moisturizing the soap feels on skin.
• Bubbly Lather -- the amount of large, fluffy bubbles.
• Creamy Lather -- the amount of dense, lotion-like lather.

Each quality is displayed on a scale with recommended ranges so you can see at a glance whether your recipe is balanced.

Saving Results to a Formula

Once you are happy with your recipe, you can save the calculation directly to Formuley as a new formula:

1. Click the Save as Formula button below the results.
2. Enter a formula name and any notes you want to include.
3. Click Create. The formula is saved to your library with all oils, percentages, lye amounts, and water amounts pre-filled.

From there, you can open the formula in the Formula Builder to add fragrance, colorants, additives, or a procedure.

Tips for Accurate Results

• Keep your ingredient library up to date. SAP values are pulled from your ingredient data. If an ingredient is missing its SAP value, the calculator cannot include it in the lye calculation.
• Double-check your lye type. NaOH and KOH require very different amounts. Selecting the wrong type will produce an incorrect recipe.
• Start with a moderate superfat. If you are new to soap making, begin at 5% superfat and adjust based on your results.
• Run the Soap Quality Predictor alongside the Lye Calculator to get a fuller picture of how your recipe will perform. See Calculators Overview for details on all available tools.