Explore our collection of 150+ developer tools, PDF editors, and image converters. Everything runs locally in your browser.
Ubify Financial Advisory Board
FINANCIAL ANALYSTS & CPA REVIEWERS
About This Tool
The Soap Making Lye & Water Sizer calculates the exact sodium hydroxide (NaOH) lye weight and liquid water volume required to saponify a batch of base oils into handmade cold process bar soap.
### Saponification Chemistry & Formula Cold process soap making triggers an exothermic chemical reaction between triglycerides (fats/oils) and a strong alkali (sodium hydroxide, NaOH) to yield soap salts and natural glycerin: - Average Saponification Value (SAP): The calculator uses an average SAP value of 0.138 g NaOH per gram of oil, representative of balanced baseline blends combining olive oil, coconut oil, and palm or shea butter. - Raw Lye Requirement: $$\text{Raw Lye} = \text{Base Oils Weight} \times 0.138$$ - Superfat / Lye Discount: Leaving a proportion of oils unsaponified ensures free moisturizing fatty acids in the bar and guarantees zero unreacted caustic lye remains: $$\text{Lye with Superfat} = \text{round}\left(\text{Raw Lye} \times \left(1 - \frac{\text{Superfat}\%}{100}\right)\right)$$ - Water Volume: Determined by multiplying lye weight by the user-selected water-to-lye ratio (typically 2.0:1 to 2.5:1): $$\text{Water Weight} = \text{round}(\text{Lye with Superfat} \times \text{Water Ratio})$$ - Total Batch Batter Weight: $$\text{Batch Weight} = \text{Base Oils} + \text{Lye} + \text{Water}$$
### Worked Batch Example Consider crafting a bar soap batch with **1,000 g base oils**, a **5% superfat discount**, and a **2.0:1 water-to-lye ratio**: 1. **Raw Lye**: $$1000 \times 0.138 = 138.0\text{ g NaOH}$$ 2. **Superfat Discount (5%)**: $$138.0 \times (1 - 0.05) = 138.0 \times 0.95 = 131.1 \to 131\text{ g NaOH}$$ 3. **Water Requirement (2:1 Ratio)**: $$131 \times 2.0 = 262\text{ g water}$$ 4. **Total Saponification Batter**: $$1000\text{ g oils} + 131\text{ g lye} + 262\text{ g water} = 1,393\text{ g soap batter}$$
> Safety Protocol: Always pour dry lye crystals into water slowly with continuous stirring. Never pour water into dry lye, which causes immediate boiling, localized steam eruption, and caustic splashing. Always wear eye protection and gloves.
### Zero-Server Privacy Guarantee All batch calculations occur entirely in your local web browser. Recipe weights and ratios remain private on your device.
How to Use
- 1
Enter the total combined weight of your recipe base oils in grams.
- 2
Set your target superfat percentage (typically 5% for gentle body bars).
- 3
Select your water-to-lye ratio (2.0:1 is standard for reliable trace timing).
- 4
Review the exact grams of NaOH lye and water required to mix your lye solution.
Frequently Asked Questions
What is superfatting in cold process soap making?
Superfatting leaves a small percentage (typically 5% to 8%) of oils unreacted by reducing the lye amount. This provides moisturizing benefits and ensures no caustic lye remains in the finished bar.
Why must lye always be added to water rather than water to lye?
Dissolving NaOH in water generates intense exothermic heat. Adding water onto concentrated lye can cause rapid boiling and violent splashing of caustic chemical solution.
Can this calculation be used for liquid soap making?
No. Hard bar soap uses sodium hydroxide (NaOH). Liquid soap requires potassium hydroxide (KOH), which has a higher molecular weight and different saponification values.