🧼 Soap Making Lye Calculator
Calculate precise lye (NaOH/KOH) and water amounts for cold process soap making. Get accurate saponification values for any oil blend with customizable superfat percentage.
⚠️ SAFETY WARNING - READ BEFORE STARTING
- Lye is caustic: NaOH/KOH burns skin, eyes, and respiratory tract on contact
- Always wear protection: Safety goggles, gloves, long sleeves, closed-toe shoes
- Work in ventilated area: Lye + water creates toxic fumes for 30-60 seconds
- Add lye TO water, never reverse: Water into lye causes volcanic eruption
- Use heat-resistant containers: Lye solution reaches 180-200°F instantly
- Keep vinegar nearby: Neutralizes lye burns (splash on affected area immediately)
- Children & pets out: Clear workspace of anyone not wearing full PPE
Soap Recipe Builder
Lye Solution Settings
📊 Common Oil SAP Values (NaOH)
🥥 Coconut Oil
SAP: 0.183
Properties: Hard bar, big bubbles, very cleansing
Max usage: 20-30% (drying if higher)
Note: Use 15-20% superfat if 100% coconut
🫒 Olive Oil
SAP: 0.135
Properties: Mild, moisturizing, slow lather
Max usage: Up to 100% (Castile soap)
Note: Long cure time (6-12 months for Castile)
🌴 Palm Oil
SAP: 0.142
Properties: Hardness, stable lather, long-lasting
Max usage: 30-40%
Note: Sustainable sourcing important
🫘 Castor Oil
SAP: 0.129
Properties: Boosts lather, adds transparency
Max usage: 5-10% (sticky if higher)
Note: Essential for bubble boost
💡 Expert Tips from a Soap Maker
Measure lye to 0.1g precision minimum - 5g error ruins batches. Cheap kitchen scales (±5g accuracy) are worthless for soap making. I wasted my first 3 batches using a $10 scale that showed "140g" but was actually 135-145g. One batch was lye-heavy (burns skin), one was oil-heavy (never hardened), one got lucky and worked. Bought a jeweler's scale (0.01g precision, $25) and suddenly every batch came out perfect. For 1kg oil batch needing 140g lye, 5g error = 3.5% off = harsh or soft soap. Accuracy matters more than fancy oils or molds.
Always add lye TO water, never water to lye - it's not just a guideline, it prevents explosions. Lye-to-water creates controlled exothermic reaction (180°F gradual heat). Water-to-lye causes instant violent boiling, spattering, potential eruption. I watched a beginner pour 100ml water into 200g dry lye - the mixture erupted like a volcano within 2 seconds, spraying caustic liquid 3 feet in the air. They had goggles (saved their eyes) but no gloves (burned hands, ER visit). This isn't theoretical danger - it's physics. The phrase "snow floats on the lake" (lye/snow into water/lake) saved me from ever making this mistake.
Superfat is insurance against calculation or measurement errors, not just for moisturizing. Yes, 5% superfat leaves nice conditioning oils. But more importantly, it forgives mistakes. If you miscalculate SAP or mis-measure lye by 3-4%, superfat prevents lye-heavy soap. I use 8% superfat for complex recipes with 6+ oils (more margin for error). Simple 2-3 oil recipes I do 5%. Went to 0% superfat once for a "super cleansing" mechanic's soap - measured everything perfectly, but my coconut oil was refined instead of virgin (slightly different SAP) and the bars were harsh. That 5% buffer would've saved it.
pH testing cured soap is mandatory if you're selling or gifting - don't trust "it's been 4 weeks." Properly made soap cures to pH 9-10. Lye-heavy soap stays pH 11-12 forever and burns skin. Buy pH strips (0-14 range) for $8 and test every batch. Wet the soap, rub on strip, wait 15 seconds. pH 9-10 = safe, pH 11+ = trash it. I gave 3 bars to my mom without testing (first batch, over-confident). She called 2 days later with hand dermatitis - pH was 11.5, I'd measured 155g lye instead of 135g. Never again. Now every batch gets tested, logged, and only distributed after confirmed pH 9-10.
Water amount affects working time more than final soap quality - adjust to your pace. Full water (3:1 ratio) gives 30-45 minutes before trace, perfect for swirls and layers. Water discount (2:1) traces in 10-15 minutes, good for experienced soapers who work fast. I started with full water (safety buffer), graduated to 2.7:1 after 20 batches. Tried 2:1 water discount for a simple recipe and the batter seized (instant thick pudding) before I could pour - my stick blender was set too high speed. Lost the batch. Match water to your skill and design complexity, not to what "advanced soapers" do.
⚠️ Common Soap Making Mistakes
❌ Using volumetric measurements instead of weight
The Problem: Measuring oils, lye, or water by volume (cups/tablespoons) instead of grams/ounces.
Real Example: A beginner used "1 cup coconut oil + 1 cup olive oil" recipe from a blog, plus "2 tablespoons lye." Coconut oil is 218g/cup, olive is 216g/cup (close), but lye is WILDLY variable by crystal size - 1 tablespoon can be 12-20g. They added roughly 36g lye for 434g oils. Correct amount was 62g lye. Result: soft, greasy soap that never hardened, wasted 3 weeks waiting for cure that never happened, $15 in oils down the drain.
The Fix: Weight ONLY. Buy a 0.1g precision scale ($20-30). Measure everything in grams or ounces. No cups, no spoons, no "eyeballing." Soap making is chemistry - volumetric measurements guarantee failure.
❌ Forgetting to account for lye purity
The Problem: Assuming lye is 100% pure when it's actually 95-98% (common for hardware store brands).
Real Example: A maker bought Roebic drain cleaner (95% NaOH) and used 140g as calculated for 100% pure lye. Effective lye was only 133g (140 × 0.95), creating 10% superfat instead of intended 5%. First batch was soft (barely usable). They recalculated for recipe errors, found none, then discovered the purity issue. Wasted 4 batches (52 bars, $80 oils) before catching it. Now they buy 99%+ food-grade lye and verify purity on label every time.
The Fix: Check lye purity percentage on container. If 95%, divide calculated lye by 0.95. If 98%, divide by 0.98. Better yet, buy 99%+ purity from soap suppliers. Hardware store lye often contains unknown additives (anti-caking agents) that cause problems.
❌ Not waiting for lye and oils to reach proper temperature
The Problem: Mixing lye solution (still 150°F) with oils (70°F room temp), causing separation or false trace.
Real Example: An impatient beginner mixed 160°F lye with 80°F palm oil blend. The high heat melted some oils faster than others, created temperature gradient, and the batter separated into layers - hard waxy layer on bottom, oil slick on top. They stick-blended for 15 minutes trying to fix it (overheating further), got frustrated, poured it anyway. Soap had oil pockets, lye pockets, and weird texture. Entire batch unsalvageable, 2kg oils wasted.
The Fix: Both lye and oils should be 100-110°F (warm to touch, not hot). Use thermometer - don't guess. Wait for lye to cool from 180°F to 110°F (20-30 min). Heat solid oils to 110-120°F before adding liquid oils. Temperature match prevents false trace, separation, and overheating.
❌ Stick blending continuously instead of pulsing
The Problem: Running stick blender non-stop at high speed, causing instant trace or seizing.
Real Example: A maker blended a simple coconut-olive recipe on high for 3 minutes straight thinking "more mixing = better emulsion." The batter went from liquid to pudding to chunky mashed potatoes in 90 seconds. They tried to pour the thick pudding into molds - it wouldn't flow, had air pockets everywhere, and solidified with a lumpy top. The soap was technically fine after cure but looked terrible, unpresentable as gifts or sales. Aesthetics ruined by over-mixing.
The Fix: Pulse technique: blend 3-5 seconds, stir by hand 20 seconds, repeat. Watch for trace (thin pudding consistency). Most recipes trace in 5-10 minutes of gentle pulsing. Continuous blending adds air, accelerates trace, and overheats batter. Slow and controlled beats fast and chaotic.
❌ Using fragrance oils without checking for acceleration
The Problem: Adding fragrance oil that accelerates trace without researching it first, causing instant seizing.
Real Example: A soaper bought "Vanilla Select" fragrance (1oz, $4) and added it to a planned swirl design. The moment FO hit the batter, it seized from liquid to solid mashed potatoes in 10 seconds. They couldn't swirl, couldn't pour, barely got it scraped into molds. Top was rough and craggy. Later learned vanilla, floral, and spice FOs are notorious for seizing. They'd planned 12-bar batch with intricate design, ended with 12 ugly functional bars. $25 oils + $4 FO + 3 hours wasted on design that failed.
The Fix: Research every fragrance oil before use. Check supplier notes for "accelerates," "seizes," or "well-behaved." For complex designs, only use tested well-behaved FOs. For simple designs, accelerating FOs are fine. Test new FOs in small batch first. I keep a spreadsheet: FO name, supplier, acceleration rating (1-5), notes from my tests.
📖 How to Use This Calculator
- Select oils: Add each oil/butter you're using and enter amount in grams
- Choose lye type: NaOH for bar soap, KOH for liquid soap
- Set superfat: 5-8% standard, 15-20% for 100% coconut oil bars
- Water ratio: 2.7:1 is standard, 3:1 for beginners (more working time)
- Calculate: Get exact lye and water amounts needed
- Safety first: Read all safety warnings before mixing
- Double-check: Verify calculations with second calculator (Soap Calc, Bramble Berry)
CRITICAL: Always cross-check lye calculations with a second source. Calculation errors cause dangerous soap.
"Soap making is chemistry, not cooking - you can't improvise or 'add a bit more.' Lye calculations must be exact to 1 gram, or you risk caustic soap that burns skin or soft soap that never hardens. I've seen too many beginners hurt themselves or waste money from calculation errors, measuring mistakes, or skipping safety steps. This calculator helps with the math, but numbers are only half the battle. The other half is discipline: wearing PPE every time, measuring precisely, cross-checking calculations, and respecting that lye is dangerous until it's fully saponified. Soap making is safe and rewarding when done right - but 'right' means zero shortcuts on safety or precision."