Lye Calculator
Information Guide
Oil Reference
Soap Type
Batch Settings
Using Masterbatch Lye Solution?
Pre-mixed lye & water solution — calculator shows how much to use
Oils & Fats
| Oil / Fat | % | Weight (g) | SAP |
|---|
Custom Liquids
Replace water with milk, aloe, tea, beer & more
0 added
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Specify what percentage of your calculated water to replace with an alternative liquid. Total cannot exceed 100% of water. Use frozen milk & aloe ice to prevent scorching when adding lye.
| Liquid Name | Amount | Unit | % of Water | |
|---|---|---|---|---|
| No liquids added yet. | ||||
Custom Additives
Salt, clay, honey, botanicals & more
0 added
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Additives are recorded for your recipe and included in the batch total weight — they do not affect the lye calculation. Add them at the stage indicated.
| Additive | Amount | Unit | Add Stage | |
|---|---|---|---|---|
| No additives added yet. | ||||
Citric Acid
Automatically adjusts lye — chelates hard water minerals
0g
▼
Citric acid reacts with lye to form sodium/potassium citrate. The calculator automatically adds the extra lye needed. Rule: 0.725g extra NaOH (or 1.017g KOH) per 1g citric acid. Typical use: 1–3% of total oil weight. Add citric acid to your oils or at light trace — Never to the lye solution.
Extra Lye Required
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calculated after hitting Calculate
Mould Calculator
Calculate batch size from mould dimensions or volume
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Enter your mould dimensions or total volume. The calculator uses the industry-standard multiplier: 0.40 for imperial (oz) or 0.70 for metric (g). Result sets the oil weight for your recipe.
Your Soap Recipe
1000g BatchNaOH Required
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grams
Total Liquid
—
grams
Total Oil
—
grams
Superfat
5%
Batch Total
—
grams
Water:Lye Ratio
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Estimated Fatty Acid Profile
Soap Qualities
Notes
Water Calculation Methods
Choose how you want to determine your water amount. Each method suits different experience levels and soap styles.
Choose how you want to determine your water amount. Each method suits different experience levels and soap styles.
| Method | How It Works | Typical Range | Best For |
|---|---|---|---|
| Water as % of Oils | Water = Total Oil Weight × % | 33–40% | Beginners |
| Water:Lye Ratio | Water = Lye Amount × Ratio | 2:1 – 3:1 | Intermediate |
| Lye Concentration % | Water = Lye × (100 – %) / % | 25–35% | Advanced |
💡 Water Quick Tips
• % of Oils (38%) — Best starting point for beginners. Higher water = slower trace but longer cure.
• Water:Lye Ratio (2.5:1) — Great for precise control. Lower ratio = harder, faster unmould.
• Lye Concentration (30–33%) — Preferred by hot-process soapers. Higher concentration = faster saponification.
• For milk soaps, use frozen liquid (ice cubes) to prevent scorching and discolouration.
• % of Oils (38%) — Best starting point for beginners. Higher water = slower trace but longer cure.
• Water:Lye Ratio (2.5:1) — Great for precise control. Lower ratio = harder, faster unmould.
• Lye Concentration (30–33%) — Preferred by hot-process soapers. Higher concentration = faster saponification.
• For milk soaps, use frozen liquid (ice cubes) to prevent scorching and discolouration.
🧪 Superfat Quick Guide
Superfat (also called lye discount) is the percentage of oils not saponified — left over to condition skin.
• 0–3% — Hard, long-lasting bar. Good for shampoo bars.
• 4–6% — Most popular range. Balanced cleansing & conditioning. (5% recommended for starters)
• 7–10% — Extra conditioning. Ideal for sensitive & dry skin.
• 10%+ — Very conditioning but softer bar; may go rancid faster. Use sparingly.
Tip: Soapmaking is not an exact science — a small superfat buffer protects against measurement errors.
Superfat (also called lye discount) is the percentage of oils not saponified — left over to condition skin.
• 0–3% — Hard, long-lasting bar. Good for shampoo bars.
• 4–6% — Most popular range. Balanced cleansing & conditioning. (5% recommended for starters)
• 7–10% — Extra conditioning. Ideal for sensitive & dry skin.
• 10%+ — Very conditioning but softer bar; may go rancid faster. Use sparingly.
Tip: Soapmaking is not an exact science — a small superfat buffer protects against measurement errors.
⚗️ Lye Purity Guide
Most commercially sold lye is 98–99% pure. Always check the label on your supplier's product.
• 100% — Use only if you've verified purity (e.g. lab-grade reagent).
• 99% — Typical for quality food/soap-grade NaOH such as Soapmaid NaOH.
• 98% — Common. The calculator automatically adjusts the lye amount upward to compensate.
• 90% — Pool-grade or industrial lye. Typically used for KOH liquid soap. Always check purity with your supplier.
Lower purity = calculator uses more lye to hit the same saponification target.
Most commercially sold lye is 98–99% pure. Always check the label on your supplier's product.
• 100% — Use only if you've verified purity (e.g. lab-grade reagent).
• 99% — Typical for quality food/soap-grade NaOH such as Soapmaid NaOH.
• 98% — Common. The calculator automatically adjusts the lye amount upward to compensate.
• 90% — Pool-grade or industrial lye. Typically used for KOH liquid soap. Always check purity with your supplier.
Lower purity = calculator uses more lye to hit the same saponification target.
🌿 Citric Acid in Soap
Citric acid reacts with NaOH to form sodium citrate — a chelating agent that improves lather in hard water & extends shelf life. It consumes additional lye.
• Typical usage: 1–3% of total oil weight (e.g. 10–30g per 1000g oils).
• Rule of thumb: Add 0.725g extra NaOH per 1g of citric acid used.
• Add citric acid to your oils phase or at light trace — never to the lye solution.
Citric acid reacts with NaOH to form sodium citrate — a chelating agent that improves lather in hard water & extends shelf life. It consumes additional lye.
• Typical usage: 1–3% of total oil weight (e.g. 10–30g per 1000g oils).
• Rule of thumb: Add 0.725g extra NaOH per 1g of citric acid used.
• Add citric acid to your oils phase or at light trace — never to the lye solution.
⚗️ Hybrid Soap (Dual Lye) Guide
Hybrid soap uses both NaOH and KOH together, producing a soap with unique properties valued for shave soap, cream soap, and specialty bars.
• What it does: NaOH creates hardness & longevity; KOH adds creaminess, lather, and water solubility.
• Classic ratios: 60% KOH / 40% NaOH for shave soap · 50/50 for cream soap · 5% KOH / 95% NaOH for Castile (reduces sliminess).
• Important: The calculator uses each oil's correct SAP value for each lye independently — you cannot simply split a single lye total, as KOH molecules weigh 1.403× more than NaOH molecules.
• KOH purity: Typically 90% — always check your supplier's certificate. NaOH is usually 99%.
• Process tip: Add each lye to the liquid separately, fully dissolving one before adding the next.
Hybrid soap uses both NaOH and KOH together, producing a soap with unique properties valued for shave soap, cream soap, and specialty bars.
• What it does: NaOH creates hardness & longevity; KOH adds creaminess, lather, and water solubility.
• Classic ratios: 60% KOH / 40% NaOH for shave soap · 50/50 for cream soap · 5% KOH / 95% NaOH for Castile (reduces sliminess).
• Important: The calculator uses each oil's correct SAP value for each lye independently — you cannot simply split a single lye total, as KOH molecules weigh 1.403× more than NaOH molecules.
• KOH purity: Typically 90% — always check your supplier's certificate. NaOH is usually 99%.
• Process tip: Add each lye to the liquid separately, fully dissolving one before adding the next.
🧪 Masterbatch Lye Guide
A masterbatch is a concentrated lye-water solution made in advance and stored safely — saving time and reducing the hazard of dissolving lye every session.
• How it works: Mix lye and water at your chosen concentration. The most popular is 50% — equal weights of lye and water. Store in a clearly labelled, airtight HDPE container away from children and pets.
• 50% masterbatch rule: Measure out double the lye weight from your solution (it's half lye, half water), then add any extra water your recipe still requires.
• Using the calculator: Enable the Masterbatch toggle in Batch Settings, enter your concentration %, and the calculator shows exactly how much solution to measure plus any additional water needed.
• Safety: A pre-made lye solution is still caustic — treat it with the same care as freshly mixed lye. Always label containers clearly with the concentration, lye type, and date made.
• Shelf life: NaOH solutions stay stable for 3–6 months in airtight containers. KOH solutions absorb CO₂ from air — best used within 1–2 months.
• Hybrid masterbatch: Batch NaOH and KOH separately and combine only when making soap — never store them pre-mixed.
A masterbatch is a concentrated lye-water solution made in advance and stored safely — saving time and reducing the hazard of dissolving lye every session.
• How it works: Mix lye and water at your chosen concentration. The most popular is 50% — equal weights of lye and water. Store in a clearly labelled, airtight HDPE container away from children and pets.
• 50% masterbatch rule: Measure out double the lye weight from your solution (it's half lye, half water), then add any extra water your recipe still requires.
• Using the calculator: Enable the Masterbatch toggle in Batch Settings, enter your concentration %, and the calculator shows exactly how much solution to measure plus any additional water needed.
• Safety: A pre-made lye solution is still caustic — treat it with the same care as freshly mixed lye. Always label containers clearly with the concentration, lye type, and date made.
• Shelf life: NaOH solutions stay stable for 3–6 months in airtight containers. KOH solutions absorb CO₂ from air — best used within 1–2 months.
• Hybrid masterbatch: Batch NaOH and KOH separately and combine only when making soap — never store them pre-mixed.
SAP Values Reference — Saponification values used to calculate lye requirements per gram of oil.
| Oil / Fat | NaOH SAP | KOH SAP |
|---|