liminfoSoap Making Calculator
Free web tool: Soap Making Calculator
Soap Making Calculator (Lye Calculator)
Enter oil weights to calculate lye (NaOH/KOH) and water amounts. All weights in grams.
Typical: 3–8%
Typical: 33–40%
Oils (grams)
Safety Warning
- • Always add lye to water, never water to lye.
- • Wear protective gloves, goggles, and long sleeves when handling lye.
- • Work in a well-ventilated area.
- • Always verify calculations with a trusted lye calculator before making soap.
About Soap Making Calculator
The Soap Making Lye Calculator computes the precise amount of lye (sodium hydroxide NaOH for bar soap, or potassium hydroxide KOH for liquid soap) needed for a cold-process soap batch based on the weight of each oil used. Each oil has a unique saponification value — the amount of lye required to fully saponify one gram of that oil — and this calculator applies the correct SAP value for each of the 10 supported oils: olive oil, coconut oil (76°), palm oil, shea butter, castor oil, avocado oil, sweet almond oil, sunflower oil, cocoa butter, and jojoba oil.
The calculator supports two key adjustable parameters. Superfat (%) controls how much of the oils are intentionally left unsaponified to add skin-conditioning properties to the finished soap; a typical range is 3–8%. Water ratio (% of total oils) controls how much water is added to dissolve the lye before mixing; a typical range is 33–40%. Adjusting these parameters lets you customize the hardness, lather, and conditioning properties of your soap formulation.
For any entered oil combination, the tool outputs: total oil weight, lye amount after superfat reduction, water amount, total batch weight, and a per-oil breakdown table showing each oil's weight and percentage of the blend. A prominent safety warning reminds users of critical lye handling precautions, as lye is a highly caustic substance that requires proper protective equipment and ventilation.
Key Features
- Supports 10 common soap-making oils with accurate NaOH and KOH SAP values
- Calculates NaOH for bar soap or KOH for liquid soap — switchable with one click
- Adjustable superfat percentage (0–25%) to control skin-conditioning level
- Adjustable water ratio (20–50% of oil weight) to customize lye solution concentration
- Real-time output: lye amount, water amount, and total batch weight
- Per-oil breakdown table showing weight and percentage of each oil in the blend
- Prominent safety warnings for lye handling with protective equipment reminders
- 100% client-side — no recipe data is uploaded or stored
Frequently Asked Questions
What is saponification and why does it matter for soap making?
Saponification is the chemical reaction between a fat/oil and an alkali (lye) that produces soap and glycerin. Each oil has a specific saponification value (SAP value) — the exact amount of NaOH or KOH required to fully convert one gram of that oil into soap. Using the wrong amount of lye produces soap that is either caustic (too much lye) or greasy (too little lye).
What is the difference between NaOH and KOH for soap making?
Sodium hydroxide (NaOH, caustic soda) produces hard bar soap. Potassium hydroxide (KOH, potash lye) produces liquid or soft soap. This calculator uses the appropriate SAP value for each oil depending on which lye type you select.
What is superfat and what percentage should I use?
Superfat is the percentage of oils intentionally left unsaponified in the finished soap. These excess oils add moisturizing and conditioning properties. A 5% superfat is common for beginners. Higher superfat (8%+) gives a more moisturizing soap but reduces lather and shelf life. Lower superfat (0–3%) is used for shaving soaps.
What water ratio should I use?
The water ratio controls the concentration of the lye solution. A 33–38% water-to-oil ratio is standard for most recipes. Higher water content (38–40%) makes the soap softer initially but takes longer to cure. Lower water content (28–33%) produces a harder bar faster but requires more care during mixing due to the faster reaction speed.
Why does this calculator include a safety warning?
Lye (NaOH and KOH) is a highly corrosive alkali that can cause severe chemical burns on skin, eyes, and airways. When lye is mixed with water, it generates significant heat (an exothermic reaction). Safe handling requires protective gloves, goggles, long sleeves, and adequate ventilation. The calculator always reminds users of these precautions.
What does the oil breakdown table show?
The oil breakdown table lists each oil you have entered with its weight in grams and its percentage of the total oil blend. This helps you verify that your formulation matches your intended recipe ratios — for example, confirming that coconut oil makes up 30% of the blend as intended.
Can I use oils not listed in the calculator?
The current version supports 10 oils with pre-loaded SAP values. If you use an oil not listed (such as hemp seed oil or mango butter), you would need to manually account for its lye requirements using its known SAP value from soap-making reference tables, then add it to the total manually.
How accurate are the SAP values used in this calculator?
The SAP values are based on widely referenced soap-making literature. NaOH values include: olive oil 0.1353, coconut oil (76°) 0.1910, palm oil 0.1413, shea butter 0.1282, castor oil 0.1286, avocado oil 0.1339, sweet almond oil 0.1367, sunflower oil 0.1354, cocoa butter 0.1378, jojoba oil 0.0695. KOH values are approximately 1.40x the NaOH values.