Soap Calculator — Free Lye & Soap Making Studio

Calculate NaOH & KOH lye amounts, water ratios, batch sizes, fragrance loads, and profit margins — all in one free tool.

25+ Oils NaOH & KOH No Sign-up Mobile Friendly 100% Free

🧪 Lye Calculator (NaOH & KOH)

Unit
Soap type
KOH purity %
Superfat
5%
Water ratio
38%

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How to Use the Soap Calculator

Using our soap calculator is simple, even for beginners. Follow these steps to generate a safe, balanced soap recipe in under two minutes.

Choose your soap type. Select Bar Soap (NaOH) for a traditional solid bar, or Liquid Soap (KOH) for a soft or pourable soap. The calculator automatically uses the correct lye type and saponification values.
Add your oils. Type any oil name in the search box — the calculator includes 25+ common soap making oils. Enter the weight and click Add Oil. Add as many oils as your recipe requires.
Set your superfat. Use the superfat slider to choose how much oil will remain unsaponified. 5% is ideal for most recipes — it creates a safety buffer and adds conditioning properties without reducing hardness significantly.
Adjust the water ratio. The water slider controls how much water you'll use relative to your oils. 38% is a reliable default. Lower ratios (33–36%) produce faster-tracing soap that unmolds sooner.
Read your results. Instantly see your NaOH or KOH amount, water amount, total batch weight, lye concentration, fatty acid profile, and quality ratings for cleansing, hardness, conditioning, and lather.
Continue with other tools. Click Send to Cost Calculator to price your batch, or use the Batch Scaler to resize your recipe. The Fragrance Calculator helps you measure your scent at the right usage rate.

Soap Oil Properties & Fatty Acid Guide

Each oil brings different properties to soap based on its fatty acid composition. Lauric and myristic acids (found in coconut and palm kernel) create hard bars with big bubbly lather. Oleic acid (olive, avocado, almond) is responsible for a moisturizing, creamy lather. Ricinoleic acid from castor oil boosts lather stability and conditioning uniquely.

Oil NaOH SAP Hardness Cleansing Conditioning Best for
Coconut Oil0.190⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐⭐Lather & hardness
Olive Oil0.134⭐⭐⭐⭐⭐⭐⭐⭐⭐Conditioning castile
Palm Oil0.141⭐⭐⭐⭐⭐⭐⭐⭐⭐Hardness & stable lather
Castor Oil0.129⭐⭐⭐⭐⭐⭐⭐Lather booster (max 10%)
Shea Butter0.128⭐⭐⭐⭐⭐⭐⭐⭐Conditioning & hardness
Lard / Tallow0.138⭐⭐⭐⭐⭐⭐⭐⭐⭐Hard, creamy lather bar
Sweet Almond0.136⭐⭐⭐⭐⭐⭐⭐Skin-gentle bars
Avocado Oil0.133⭐⭐⭐⭐⭐⭐⭐Luxury conditioning
Cocoa Butter0.137⭐⭐⭐⭐⭐⭐⭐⭐Hardness & moisturizing
Canola Oil0.124⭐⭐⭐⭐⭐⭐⭐Budget conditioning

SAP values are per gram of oil for NaOH. Multiply by 1.403 for KOH (at 100% purity). All values in this calculator are sourced from established saponification value tables.

Frequently Asked Questions

A soap calculator computes the exact amount of lye (sodium hydroxide for bar soap or potassium hydroxide for liquid soap) needed to saponify your chosen oils. It uses saponification values (SAP values) unique to each oil to ensure your recipe is safe, properly balanced, and customized to your desired superfat level.

The lye amount depends on which oils you use and your desired superfat. Each oil has a unique SAP value — for example, 500g of olive oil at 5% superfat requires approximately 63.65g of NaOH. Use this soap calculator: enter your oils and weights, set your superfat, and the lye and water amounts are calculated instantly.

Superfat (also called lye discount) is the percentage of oils intentionally left unsaponified in your soap. A 5% superfat means 5% of the oils remain as free conditioning oils. Most cold process soaps use 5–8% superfat. It provides a safety margin against lye-heavy soap and adds skin-conditioning properties, though higher superfat can reduce hardness and shelf life.

Yes — finished, properly cured soap contains zero free lye. During saponification, the lye chemically reacts with the oils to form soap (sodium or potassium salts of fatty acids) and glycerin. Once the reaction is complete, no lye remains. Always handle raw lye with proper safety gear, but well-made soap is completely safe for skin.

NaOH (sodium hydroxide) produces hard bar soap. KOH (potassium hydroxide) produces soft or liquid soap. KOH creates a softer, more water-soluble soap molecule. KOH is typically sold at 90% purity, so the calculator applies a purity correction. Both require different SAP values — our calculator handles both automatically when you toggle soap type.

Cold process soap typically uses 2–3% fragrance oil by total oil weight. For example, 500g of oils needs 10–15g of fragrance. Always verify the supplier's maximum usage rate and IFRA safety data for each fragrance. Use our Fragrance Calculator tab to compute precise amounts and split multiple scents by percentage.

Yes — the lye calculation is identical for both cold process and hot process soap. The same NaOH amount, superfat, and water ratio apply regardless of the method. Hot process accelerates saponification with heat (slow cooker, oven, or stovetop), allowing the soap to be used sooner, but the underlying chemistry and lye amounts are the same.

A beginner-friendly recipe is 30% coconut oil, 30% palm oil (or lard), 30% olive oil, and 10% castor oil. Coconut provides cleansing and lather, palm/lard adds hardness and stable lather, olive gives conditioning, and castor boosts lather. Try 500g total oils, 5% superfat, 38% water ratio in this calculator to get started.