What is a soap calculator?

A soap calculator is a tool that calculates 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) to ensure your recipe is safe, fully saponified, and customized to your desired superfat level.

How much lye do I need for soap?

The lye amount depends on which oils you use and your desired superfat percentage. Each oil has a unique SAP value. For example, 500g of olive oil at 5% superfat requires approximately 63.65g of NaOH. Our soap calculator computes this instantly for any combination of oils.

What is superfat in soap making?

Superfat (also called lye discount) is the percentage of oils left unsaponified in your soap. A 5% superfat means 5% of the oil remains as free oil, making the soap more moisturizing and providing a safety buffer. Most cold process soaps use 5–8% superfat. Higher superfat makes softer, more conditioning soap but can reduce lather and shelf life.

Can I use KOH instead of NaOH for bar soap?

NaOH (sodium hydroxide) produces solid bar soap, while KOH (potassium hydroxide) produces liquid or soft soap. You can use KOH for bar soap at higher concentrations, but it's not traditional. Our soap calculator supports both lye types and adjusts for KOH purity (typically 90%).

How do I calculate water for soap making?

Water in soap is typically calculated as a percentage of total oil weight, ranging from 33% to 40%. A 38% water-to-oil ratio is a common starting point. Our soap calculator lets you adjust this ratio with a slider. Less water produces faster-tracing soap that unmolds sooner; more water gives you more time to work with the batter.

What oils make hard soap with good lather?

Coconut oil and palm kernel oil create hard soap with big bubbly lather due to their high lauric and myristic acid content. Palm oil, lard, and tallow add hardness via palmitic and stearic acids. Castor oil boosts lather stability and conditioning. Our soap calculator shows quality ratings including hardness, lather, and conditioning for your recipe.

How much fragrance oil do I add to soap?

Most cold process soap recipes use 2–3% fragrance oil by weight of oils. For example, 500g of oils would require 10–15g of fragrance oil at 2–3%. Always check your fragrance supplier's recommended usage rate and IFRA guidelines for safety. Use our Fragrance Calculator tab to compute exact amounts.

Is lye dangerous in finished soap?

No — when properly made, finished soap contains no lye. During saponification, the lye completely reacts with the oils to form soap (sodium/potassium salts of fatty acids) and glycerin. This chemical reaction is irreversible. Always handle raw lye with gloves and eye protection, but properly cured soap is completely safe.

What is the difference between cold process and hot process soap?

Cold process soap is mixed at room temperature and left to saponify over 24–48 hours before unmolding, then cured for 4–6 weeks. Hot process soap is cooked (in a slow cooker or oven) which accelerates saponification — it can be used sooner but is harder to swirl or layer. The same lye calculation applies to both methods.

What is pumpkin seed oil good for in soap making?

Pumpkin seed oil is rich in linoleic acid (about 46%) and oleic acid (34%), making it a conditioning oil that produces a soft, skin-nourishing lather. It adds a beautiful golden color to cold process soap naturally. Its NaOH SAP value is 0.135 — use our soap calculator to add pumpkin seed oil to your recipe at up to 15–20% for best results. It is a popular choice for fall or harvest-themed soap recipes.

How much fragrance oil per pound of wax for candles?

The standard fragrance load for candles is 6–10% by weight of wax. For soy wax, use 1 oz of fragrance oil per pound of wax (6.25%) as a starting point, up to a maximum of 1.6 oz per pound (10%). For paraffin, you can go up to 1.9 oz per pound (12%). Our Candle Making Calculator automatically computes fragrance amounts in both grams and ounces for any wax weight and load percentage.

What wax is best for scented candles — soy or paraffin?

Soy wax is natural, clean-burning, and holds 6–10% fragrance load — great for eco-friendly container candles. Paraffin has superior fragrance throw and holds up to 12% fragrance, making it the industry standard for strong-scented candles. Coconut wax is a premium option with excellent scent throw at 6–12%. Use our Candle Making Calculator to compare fragrance amounts and pour temperatures for each wax type.

What is fragrance load in candle making?

Fragrance load is the percentage of fragrance oil added relative to the weight of wax. For example, an 8% fragrance load in 500g of soy wax equals 40g (1.4 oz) of fragrance oil. Exceeding your wax's maximum fragrance load causes seeping, poor hot throw, and fire hazards. Each wax type has a recommended range — soy: 6–10%, paraffin: 6–12%, beeswax: 3–6%, coconut: 6–12%.

How do I calculate how much wax I need for candles?

To calculate wax needed: (1) Measure your container volume in fluid ounces, (2) multiply by 0.86 to get wax weight in ounces (wax is less dense than water), (3) add fragrance weight. For example, an 8 oz jar needs about 6.9 oz of soy wax plus fragrance. Our Candle Making Calculator lets you enter wax weight in grams or ounces and automatically computes total fragrance, scent breakdown by blend percentage, burn time, and cost per candle.

How much lye do I need per pound of oil for soap?

Lye amount per pound of oil depends on which oils you use. For a typical olive oil soap at 5% superfat: approximately 1.94 oz of NaOH per pound of oil. For a coconut oil soap: about 2.73 oz NaOH per pound. Always calculate exactly using our free soap calculator — never estimate by hand. Enter your oils and weights in ounces, set your superfat, and get precise NaOH and water amounts instantly.

What is the best oil for beginner soap making?

The best beginner soap recipe is a simple olive oil and coconut oil combination: 70% olive oil for conditioning and 30% coconut oil for hard, bubbly lather. This gives a balanced, slow-tracing soap that's easy to work with. Add 5% castor oil to boost lather stability. Our soap calculator includes 12 preset starter recipes — from basic castile soap (100% olive) to classic shaving bars — making it easy for beginners to start with a proven formula.

Can I substitute palm oil in soap recipes?

Yes — palm oil can be replaced with lard or tallow (same palmitic/stearic acid profile), or a blend of 50% shea butter plus 50% cocoa butter for a vegan alternative. Mango butter and kokum butter also work well as palm oil substitutes. Use our Oil Substitution Finder in the Lye Calculator tab: select palm oil and it shows the top 4 alternatives ranked by fatty acid similarity score, so you can swap like-for-like.

How do I scale a soap recipe up or down?

To scale a soap recipe: divide each oil weight by the original total oil weight, then multiply by your new target oil weight. For example, if your recipe uses 500g of oils and you want 1000g, multiply every ingredient (oils, lye, water) by 2. Our free Batch Scaler calculator does this automatically — paste your recipe, enter a target weight or bar count × bar weight, and get scaled amounts with one click.

Soap Calculator — Free NaOH & KOH Lye Calculator

Lye Calculator (NaOH & KOH)

Unit

Soap type

KOH purity % (typically 90%)

Superfat

Water ratio

38%

Add Oils to Your Recipe

No oils added yet. Search and add oils above.

Recipe Results

Add oils to see your recipe calculations.

How to Use the Soap Calculator

Using our soap calculator is straightforward, even for beginners. Follow these steps to generate a safe, balanced soap recipe in under two minutes. For a deeper understanding of the math, see the saponification guide below.

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 switches to the correct lye type and saponification values.
Add your oils. Type any oil name in the search box — the calculator includes 110+ soap making oils with accurate SAP values. Enter the weight and click Add Oil. Repeat for each oil in your recipe. See the oil properties guide to understand what each oil contributes.
Set your superfat. Use the superfat slider to choose how much oil will remain unsaponified. 5% is ideal for most cold process recipes — it creates a safety buffer and adds conditioning without significantly reducing hardness.
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.
Save or share your recipe. Click Save Recipe to store it in your browser, or Share to generate a URL you can send to anyone. Switch to Cost & Profit, Batch Scaler, or Fragrance tabs to finish planning your batch.

Soap Oil Properties & Fatty Acid Guide

Each oil contributes 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) produces a moisturizing, creamy lather. Ricinoleic acid — unique to castor oil — boosts both lather stability and conditioning. See the FAQ for guidance on which oils to combine for your goals.

Common Soap Making Oils — Saponification Values & Properties
Oil	NaOH SAP	Hardness	Cleansing	Conditioning	Best for
Coconut Oil	0.190	High	High	Low	Lather & hardness
Olive Oil	0.134	Low	Low	High	Conditioning castile
Palm Oil	0.141	Good	Low	Med	Hardness & stable lather
Castor Oil	0.129	Low	Low	High	Lather booster (max 10%)
Shea Butter	0.128	Med	Low	Good	Conditioning & hardness
Lard / Tallow	0.138–0.140	Good	Low	Med	Hard, creamy lather bar
Sweet Almond Oil	0.136	Low	Low	Good	Skin-gentle bars
Avocado Oil	0.133	Low	Low	Good	Luxury conditioning
Cocoa Butter	0.137	Good	Low	Med	Hardness & moisturizing
Canola Oil	0.124	Low	Low	Good	Budget conditioning

SAP values are grams of lye per gram of oil for NaOH. Multiply by 1.403 for KOH at 100% purity. All values sourced from established saponification tables.

Understanding Saponification

Saponification is the chemical reaction between a fat (or oil) and an alkali (NaOH or KOH) that produces soap and glycerin. Every triglyceride molecule in the oil reacts with three molecules of sodium or potassium hydroxide to yield three fatty acid salt molecules (soap) and one glycerol molecule.

The saponification value (SAP value) of an oil is the number of milligrams of KOH required to completely saponify one gram of that oil. This calculator converts those values to usable gram weights of NaOH or KOH. Because every oil has a different fatty acid composition, each has a unique SAP value — coconut oil's high lauric acid content gives it a much higher SAP (0.190) than olive oil (0.134).

The superfat (lye discount) in the formula below ensures a small safety margin of unsaponified oil remains in the finished bar, both to prevent lye-heavy soap and to add conditioning free fatty acids:

Lye needed = Σ (oil weight × SAP value) × (1 − superfat%)

This is the exact formula this soap calculator uses. The step-by-step guide above walks you through entering it for your recipe.

Candle Scents & Candle Making Calculator Guide

Our candle making calculator helps you compute exact fragrance amounts for any wax weight, blend multiple candle scents, estimate burn time, and calculate cost per candle — all in one tool. Use the Candle Maker tab above to get started.

How Much Fragrance Do I Add to Candles?

The right amount of candle fragrance oil depends on your wax type. The standard rule is:

Fragrance (g) = Wax weight (g) × Fragrance load %

For example, a 500 g soy wax candle at 8% fragrance load needs 40 g of fragrance oil. Recommended fragrance loads by wax:

Candle Fragrance Load by Wax Type
Wax Type	Min Load	Max Load	Recommended	Notes
Soy Wax	6%	10%	8%	Natural, clean-burning; exceeding 10% causes fragrance seeping
Paraffin Wax	6%	12%	10%	Best fragrance throw; holds the highest fragrance load
Beeswax	3%	6%	5%	Natural honey scent; low fragrance capacity
Coconut Wax	6%	12%	10%	Excellent scent throw; creamy finish for luxury candles
Wax Blends	6%	10%	8%	Varies by formulation — check supplier recommendation

Popular Candle Scents

The most popular candle scents blend well with most waxes. Classic categories include:

Floral: Lavender, Rose, Jasmine, Peony, Gardenia — relaxing and universally loved
Fresh & Clean: Cotton, Linen, Sea Breeze, Rain, Eucalyptus — light and airy
Warm & Cozy: Vanilla, Sandalwood, Amber, Patchouli — long-lasting, complex base notes
Seasonal: Cinnamon, Pumpkin Spice, Pine, Peppermint, Mulled Wine — holiday best-sellers
Citrus: Lemon, Grapefruit, Orange, Bergamot — energizing top notes, fade faster
Gourmand: Caramel, Coffee, Baked Goods, Coconut — sweet and indulgent

Use our candle calculator's Scent Blend section to combine multiple fragrances and see exact gram amounts for each scent in your blend.

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 the 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. See the oil properties guide for more detail.
: Cold process soap is mixed at room temperature and left to saponify over 24–48 hours before unmolding, then cured for 4–6 weeks. Hot process soap is cooked (slow cooker, oven, or stovetop) to accelerate saponification — usable sooner but harder to swirl or layer. The same lye calculation in this soap calculator applies to both. See Understanding Saponification for the chemistry.
: A water discount (also called water reduction) means using less water than the full amount in your lye solution. The standard water ratio is about 38% of total oil weight, giving roughly 33% lye concentration. Reducing water to 30–33% of oils produces a higher lye concentration (36–40%), which accelerates trace, speeds unmolding, and reduces gel phase risk — especially useful in hot climates or when using fragrance oils that accelerate. This calculator's water ratio slider lets you dial in your exact water discount.
: Yes. Milk (goat, cow, coconut, oat), teas, herbal infusions, aloe vera juice, and coffee can replace all or part of the water in your lye solution. The lye amount stays exactly the same — the lye calculation only changes based on oils. For milk soaps, freeze the milk and add lye to frozen milk slowly to prevent scorching sugars. Coffee and tea add antioxidants and natural colorants. Always calculate with this soap calculator using your oil weights, then substitute your liquid of choice for the water amount shown.
: Trace is the point in cold process soap making when the oils and lye solution have emulsified enough that the mixture thickens and holds a drizzle mark on its surface — like a light pudding. Light trace is ideal for detailed swirls; medium trace works for layers; heavy trace is needed for embeds or peaks. Trace is reached faster with stick blenders, high-stearic oils (tallow, lard), certain fragrance oils, or warm temperatures. Castor oil and soft oils like sunflower slow trace.
: Soda ash is a white, powdery or feathery layer that forms on the surface of cold process soap when unsaponified soap molecules react with carbon dioxide in the air. It is harmless and doesn't affect the soap's quality. To prevent it: pour at a warmer trace, use sodium lactate, cover the mold with plastic wrap, or insulate to encourage gel phase. Soda ash washes off with the first use or can be removed by steaming, planing, or spraying with 91% isopropyl alcohol immediately after pour.
: Conditioning comes from oleic, linoleic, linolenic, and ricinoleic fatty acids. Olive oil (75% oleic), avocado oil (70% oleic), sweet almond oil (69% oleic), and hazelnut oil (78% oleic) are top conditioning oils. Hemp seed oil (57% linoleic, 20% linolenic) and rosehip oil add polyunsaturated acids that are deeply nourishing. Castor oil contributes ricinoleic acid, which is both conditioning and boosts lather. Aim for a conditioning score of 44–69 using this calculator's quality ratings. See the oil properties guide for a comparison.
: Measure your mold's interior volume in cubic inches (length × width × depth). Multiply by 0.4 to get approximate oil weight in ounces, or multiply cubic inches by 11.35 to get grams of oil. For example, a 9″ × 3.5″ × 2.5″ loaf mold = 78.75 cubic inches × 11.35 ≈ 894g of oils. Enter that oil weight into this calculator, distribute across your chosen oils, and the lye and water amounts calculate automatically. The Batch Scaler tab can then scale any saved recipe up or down to match your mold exactly.
: Most cold process soap makers use a lye concentration between 30–40%. The classic 38% water ratio produces around 33% lye concentration. A 33% water ratio gives roughly 37% lye concentration — this speeds unmolding, reduces water weight, and minimizes DOS (dreaded orange spots) by limiting excess water. For milk soaps and fragrances that accelerate, lower concentration (30–33%) gives more working time. This soap calculator shows lye concentration automatically — adjust the water ratio slider to see how it changes.
: Yes — 100% coconut oil soap is a classic, called "shampoo bar" or "Grandma's Lye Soap." It produces a very hard, white bar with excellent cleansing and lather. However, it can be drying for some skin types due to high lauric acid. To compensate, use a higher superfat of 15–20% (vs the usual 5%) when making 100% coconut soap — this leaves enough free oil to condition the skin. Try it in this calculator: add Coconut Oil (76°) at 500g, set superfat to 20%, and see how the quality ratings change.
: Saponification is an exothermic reaction — it generates heat. "Volcanoeing" or "overheating" happens when the soap mass reaches temperatures above 82°C (180°F), causing it to bubble, erupt from the mold, and develop a translucent, sticky gel with a harsh lye-heavy surface. It's common with high-sugar additives (honey, milk, beer), insulating the mold too much, or pouring at high temperature. Prevention: pour at room temperature, don't insulate sugary batches, use a water discount, and soap in a cooler environment. The soap is usually still usable after full cure.
: Yes. Popular natural colorants include: activated charcoal (black), turmeric (yellow-gold), spirulina (green), madder root (pink-red), indigo powder (blue-grey), rose clay (pink), French green clay (green), paprika (orange-tan), and cocoa powder (brown). Note that plant-based colorants can morph or fade in the high-pH environment of cold process soap — some work better in hot process or melt-and-pour. Micas and iron oxides (technically mineral pigments) are widely used and give consistent, stable color results in cold process.
: A masterbatch is a large, pre-mixed batch of lye solution (typically 50% lye concentration: equal weights of lye and water) stored safely for future use. Instead of mixing lye fresh each time, you dilute the masterbatch with additional water to your target concentration. This saves time, reduces fume exposure, and ensures consistent results. To use: calculate your full lye amount with this soap calculator, mix at 50% concentration, store in labeled HDPE or glass containers, and dilute before use. Always label with "DANGER: LYE SOLUTION" and keep out of reach of children.
: Handmade cold process soap retains naturally-occurring glycerin (a humectant that attracts moisture to skin), which is typically removed from commercial soap for use in lotions. Commercial "soap" is often a synthetic detergent bar (sodium lauryl sulfate-based) with minimal skin-beneficial ingredients. Handmade soap's quality depends entirely on the recipe — that's why balancing fatty acids with this soap calculator matters. A well-formulated soap with a 5–8% superfat, good conditioning oils, and a 4–6 week cure creates a genuinely skin-friendly bar that many people with dry or sensitive skin prefer.
: A shampoo bar uses the same NaOH lye calculation as bar soap but with a recipe that emphasizes cleansing and lather over conditioning. A popular formula: 40% coconut oil (cleansing, lather), 30% castor oil (rich lather), 20% olive oil (conditioning), 10% sweet almond oil (slip). Use a lower superfat of 2–3% to avoid waxy buildup on hair and a water ratio of 33% for a firmer bar. Load this recipe using the "Shampoo Bar" starter recipe in the calculator. Note: some people experience a 2–4 week "transition period" when switching from commercial shampoo to a bar.
: Rebatching (also called "hand-milling") involves re-melting a failed or ugly batch to fix or repurpose it. Grate or chop the soap, add a small amount of water (10–20% of soap weight), and melt slowly in a slow cooker or double boiler, stirring until smooth. You can add fragrance, color, or additives at this stage. Rebatching works well for riced soap (from acceleration), soap that seized, or plain unscented batches. Lye-heavy soap (zaps your tongue) can sometimes be saved by adding extra oils calculated with a lye calculator — add the missing superfat oils to the warm soap mass.
: This calculator uses verified saponification values sourced from established references including SoapCalc, Lovin Soap Studio, and published saponification tables. SAP values for natural oils can vary slightly between suppliers and growing seasons, which is why a 5% superfat safety buffer is recommended — this accounts for natural variation. For maximum safety, never reduce superfat below 2% and always use a calibrated digital scale (0.01g accuracy) for lye. The calculator is used by thousands of soap makers globally and the results match those of other reputable soap calculators like SoapCalc and Brambleberry's lye calculator.

Soap Calculator — Free NaOH & KOH Lye & Soap Making Studio

Lye Calculator (NaOH & KOH)

Add Oils to Your Recipe

Recipe Results

Soap Cost & Profit Calculator

Batch Size Scaler

Fragrance Load Calculator

Candle Making Calculator — Fragrance & Scent Guide

Soap Mold Size Calculator