Soap Calculator

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Soap Saponification Calculator
NaOH (Sodium Hydroxide – Bar Soap)KOH (Potassium Hydroxide – Liquid Soap)
Soap Recipe Results:
Lye Required: — g
Water Required: — g
Total Batch Weight: — g
function calculateSoap(){var w=parseFloat(document.getElementById('oil_weight').value);var sap=parseFloat(document.getElementById('sap_value').value);var sf=parseFloat(document.getElementById('superfat').value);var wr=parseFloat(document.getElementById('water_ratio').value);var lyeType=document.getElementById('lye_type').value;if(isNaN(w)||isNaN(sap)||isNaN(sf)||isNaN(wr)){alert('Please enter valid numeric values');return;}var rawLye=w*sap;if(lyeType==='koh'){rawLye=rawLye*1.4027;}var lyeWithDiscount=rawLye*(1-(sf/100));var waterWeight=lyeWithDiscount*wr;var totalWeight=w+lyeWithDiscount+waterWeight;document.getElementById('lyeVal').innerHTML=lyeWithDiscount.toFixed(2);document.getElementById('waterVal').innerHTML=waterWeight.toFixed(2);document.getElementById('totalVal').innerHTML=totalWeight.toFixed(2);if(document.getElementById('show_steps').checked){var steps="
Steps:
1. Base Lye: "+w+" * "+sap+" = "+rawLye.toFixed(2)+"g
2. Superfat Discount: "+sf+"% off
3. Final Lye: "+lyeWithDiscount.toFixed(2)+"g
4. Water ("+wr+":1): "+waterWeight.toFixed(2)+"g
";document.getElementById('answer').innerHTML+=steps;}}

Soap Calculator Use

A soap calculator is an essential tool for cold process and hot process soap makers. It allows you to calculate the precise amount of lye (Sodium Hydroxide or Potassium Hydroxide) needed to turn a specific weight of oils and fats into soap through a chemical process called saponification. Using this soap calculator ensures that your finished bar is safe for skin contact and has the desired moisturizing properties.

To get started, enter your total oil weight, the SAP value for the specific oil you are using, and your desired superfat percentage.

Oil Weight
The total mass of fats, butters, and oils in your recipe (measured in grams or ounces).
SAP Value
The Saponification value represents the milligrams of lye needed to saponify one gram of a specific oil. For example, Olive Oil is typically 0.135 for NaOH.
Superfat %
The percentage of oils that will remain "free" in the soap. This provides extra moisture and acts as a safety buffer against lye-heavy soap.
Water Ratio
How much water is used to dissolve the lye. A standard ratio is between 2:1 and 3:1 water to lye.

How It Works

When you mix an acid (oils/fats) with a base (lye), a chemical reaction occurs that results in soap and glycerin. This soap calculator uses a mathematical formula based on the specific SAP value of your ingredients. The formula used is:

Lye Amount = (Oil Weight × SAP Value) × (1 – Superfat % / 100)

  • Oil Weight: The starting point of your recipe.
  • SAP Value: A constant derived from the molecular weight of the fatty acids in the oil.
  • Superfatting: Reducing the lye amount by a percentage (usually 5%) to ensure no lye is left active in the bar.

Soap Calculation Example

Example: You want to make a simple soap batch using 1000g of Olive Oil with a 5% superfat and a 2.3:1 water ratio.

Step-by-step solution:

  1. Identify Oil Weight: 1000g
  2. Identify Olive Oil SAP Value: 0.135
  3. Calculate raw lye: 1000 × 0.135 = 135g NaOH
  4. Apply 5% Superfat discount: 135 × (1 – 0.05) = 128.25g
  5. Calculate water using 2.3 ratio: 128.25 × 2.3 = 294.98g
  6. Total Results: 128.25g Lye and 294.98g Water.

Common Questions

Why do I need a soap calculator?

Soap making is chemistry. If you use too much lye, the soap will be "caustic" and burn the skin. If you use too little, the soap will be oily and won't set. A soap calculator ensures the balance is perfect every time.

What is the difference between NaOH and KOH?

NaOH (Sodium Hydroxide) is used for hard bar soaps. KOH (Potassium Hydroxide) is used for liquid soaps and cream soaps. KOH requires roughly 1.4 times more mass than NaOH to saponify the same amount of oil.

What is a safe superfat percentage?

Most soap makers use a superfat of 5%. For very drying oils like Coconut Oil, a higher superfat (up to 20%) may be used. For gentle oils like Olive Oil, 2-5% is common.

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