--- title: "Soap Lye Calculator with SAP Values | Clover Radiance" description: "Free soap lye calculator: NaOH or KOH, superfat, water and fragrance for 47 oils, with bar properties, a printable recipe card and lye safety steps." url: https://cloverradiance.beauty/ --- Cold process · hot process · liquid soap # Soap Lye Calculator Lye, water and fragrance for your oils, from published SAP values, with superfat, KOH purity and the usual bar-property numbers. Everything is worked out in your browser. ## Lye is corrosive: read this before you weigh anything - **Sodium hydroxide (NaOH) and potassium hydroxide (KOH) burn skin and can blind.** Wear splash goggles and chemical-resistant gloves, and cover your arms. - **Always add lye to water, never water to lye**, slowly and stirring. It gets very hot and gives off fumes: work by an open window or outdoors and don't breathe them. - **Keep children and pets out of the room** until the lye, the solution and the fresh soap are put away. Never use aluminium, tin or zinc containers. - **Skin:** take off soaked clothing and rinse with lots of running water for at least 15 minutes. **Eyes:** rinse for 15–20 minutes and get medical help at once. **Swallowed:** don't cause vomiting; call a poison centre (US 1-800-222-1222) or your emergency number. Read the safety data sheet (SDS) for the lye you buy. Full safety notes and sources. Double-check every recipe with a second lye calculator before you make it. ## Your recipe | Weigh out | g | oz | | --- | --- | --- | | Oils and butters | 1,000.0 | 35.27 | | Sodium hydroxide (NaOH) | 138.2 | 4.87 | | Water (distilled) | 280.6 | 9.90 | | Total batch | 1,418.8 | 50.05 | - Lye concentration **33.0 %** - Water : lye **2.03 : 1** - Water **28.1 %** of oils - Superfat **5 %** | Oil | % of oils | g | NaOH (g) | | --- | --- | --- | --- | | Olive oil | 50.0 | 500.0 | 64.3 | | Coconut oil (76 °F or 92 °F) | 25.0 | 250.0 | 43.5 | | Shea butter | 20.0 | 200.0 | 24.2 | | Castor oil | 5.0 | 50.0 | 6.1 | ### Bar properties - Hardness 37 usual 29–54 - Cleansing 17 usual 12–22 - Conditioning 59 usual 44–69 - Bubbly 21 usual 14–46 - Creamy 25 usual 16–48 - Iodine 61 usual 41–70 - INS 145 usual 136–165 - usual range (SoapCalc) - this recipe ### Fatty acids in the oils - Saturated - Monounsaturated - Polyunsaturated Before you make it, run the same oils and settings through a second lye calculator and check that the lye amounts agree. ## How to use the lye calculator List your oils first. Type a name and pick it from the suggestions (47 oils, butters and fats are built in), then enter each one's weight in grams, ounces or pounds. If your recipe is written as percentages, switch to **Percentages** and give the total oil weight; the percentages must add up to 100. Then choose the lye. **NaOH** (sodium hydroxide) makes hard bar soap; **KOH** (potassium hydroxide) makes soft and liquid soap, and **Both** splits the lye between them. KOH is usually about 90 % pure, so the calculator divides by the purity you enter. **Superfat** is the share of oil deliberately left without enough lye to turn it into soap: a margin for SAP values that vary and scales that read a little high. The water can be set in three ways that describe the same thing: **lye concentration** (lye ÷ lye plus water), **water as a percentage of the oils** (38 % is SoapCalc's default) or a **water : lye ratio**. Fragrance is optional, as a percentage of the oils or in ounces per pound of oils (1 ppo = 6.25 %). ### Worked example Olive oil's SAP value is 190 mg KOH per gram. Multiply by 40.00 ÷ 56.11 (the molar masses of NaOH and KOH) to get 0.1354 g NaOH per gram of oil, so 1000 g of olive oil needs 135.4 g NaOH. With a 5 % superfat you weigh 95 % of that: **128.7 g NaOH**. At a 33 % lye concentration the water is 128.7 × 67 ÷ 33 = **261.3 g**. When the numbers look right, print the recipe card (it carries the safety notes), copy or download it, or save it in this browser. ## What the bar numbers mean The seven numbers under the recipe were popularised by SoapCalc. Each is simple arithmetic on the fatty acids of your oils, weighted by how much of each oil you use: - **Hardness**: lauric + myristic + palmitic + stearic, the saturated acids. - **Cleansing**: lauric + myristic, the short chains that make coconut, palm kernel and babassu soaps strip oil well. - **Conditioning**: oleic + linoleic + linolenic + ricinoleic, the unsaturated acids. It describes the oils, not an effect on skin. - **Bubbly**: lauric + myristic + ricinoleic. **Creamy**: palmitic + stearic + ricinoleic. - **Iodine** and **INS**: weighted averages of each oil's own values. A high iodine value means more double bonds: a softer bar that is more prone to going rancid. The shaded band is the range SoapCalc suggests comparing against: hardness 29–54, cleansing 12–22, conditioning 44–69, bubbly 14–46, creamy 16–48, iodine 41–70 and INS 136–165. SoapCalc itself calls these guidelines, and traditional soaps sit well outside them: a 100 % olive oil (castile) bar scores hardness 17 and cleansing 0. Use the numbers to compare two versions of a recipe, not as a grade. They ignore superfat, water, additives and any fatty acid outside the eight tracked, such as the palmitoleic acid in macadamia oil or the long-chain wax esters in jojoba and beeswax. ## Where the SAP values come from, and why they vary A saponification (SAP) value is the number of milligrams of potassium hydroxide that turn one gram of a fat into soap. Lab tables give it in mg KOH/g; soap calculators often write the same figure as a fraction (0.190 for olive oil) and convert it to sodium hydroxide with the ratio of the molar masses, 40.00 ÷ 56.11 ≈ 0.713 (0.135 for olive oil). The SAP values, fatty-acid profiles, iodine and INS figures here are the typical values in SoapCalc's oil list, which many hobby soap calculators share. They are averages. Real oils vary with plant variety, climate, refining and age: published saponification values run from 184 to 196 mg KOH/g for olive oil, 248 to 265 for coconut oil and 170 to 190 for shea butter, and the olive oil trade standard allows anything from 55 % to 85 % oleic acid. That spread is one reason soapmakers keep a few per cent of superfat. If your supplier gives a SAP value or a certificate of analysis for the batch you bought, add it as a custom oil. The [oil properties chart](https://cloverradiance.beauty/oil-properties-chart/) lists every oil with its published range where one exists. ## Lye safety in full Sodium hydroxide and potassium hydroxide are corrosive. NIOSH lists eye and skin burns among their effects, and poison centres treat a splash in the eye as an emergency. Soap made with the right amount of lye and left to cure is no longer caustic, but the dry lye, the lye solution and fresh soap batter are. ### Before you start - Read the safety data sheet (SDS) for the exact product you bought, and ask your supplier for it if it did not come with the order. - Wear splash-proof goggles (ordinary glasses leave gaps), chemical-resistant gloves such as nitrile, long sleeves and closed shoes. - Keep children and pets out of the room until everything is cleaned up, and store lye in its labelled, closed container out of their reach. - Use heat-resistant stainless steel or sturdy polypropylene (PP, recycling code 5) containers. NIOSH lists aluminium, tin and zinc as incompatible with sodium hydroxide. ### Mixing the lye solution - Weigh cold water into the jug first, then pour the lye into the water slowly while stirring. **Always add lye to water, never water to lye**: dissolving lye releases a lot of heat, and water poured onto solid lye can boil and spatter. - The solution gets very hot and gives off fumes for the first minute or so. Mix outdoors or beside an open window or extractor fan, and don't lean over the jug. - Keep acids such as vinegar or citric acid away from the lye: they react violently with it. ### If something goes wrong - **On skin:** take off soaked clothing and rinse with plenty of cool or lukewarm running water for at least 15 minutes (the NHS advises about an hour for chemical burns), then get medical advice. Don't put vinegar, creams or anything else on it. - **In the eyes:** rinse straight away with lots of room-temperature water for at least 15 to 20 minutes, holding the eyelids open and taking out contact lenses, and get emergency medical help. - **Swallowed:** don't make the person vomit. Call a poison centre or your emergency number at once. - **Who to call:** in the US, Poison Control on 1-800-222-1222 (or its webPOISONCONTROL online tool); in the UK, 999 in an emergency or NHS 111 for advice; in the EU, 112; elsewhere, your local emergency number or poison centre. ## Sources - SoapCalc, [Soap making oil chart](https://soapcalc.net/oil-list): SAP values, fatty-acid profiles, iodine and INS values of each oil, and the suggested property ranges shown in its [calculator](https://soapcalc.net/calculator). - Wikipedia, [Saponification value](https://en.wikipedia.org/wiki/Saponification_value): definition, the KOH-to-NaOH conversion (÷ 1.403) and published ranges for common oils, citing Gunstone, *Oils and Fats in the Food Industry* (Wiley, 2009) and Akoh & Min, *Food Lipids* (CRC Press, 2008). - International Olive Council, [Trade standard applying to olive oils and olive pomace oils](https://www.internationaloliveoil.org/wp-content/uploads/2026/07/COI-T.15NC-No.-3Rev.-22-_TRADE-STANDARD-REV-22_EN.pdf), COI/T.15/NC No 3/Rev. 22: oleic acid 55–85 % of fatty acids. - Wikipedia, [Sodium hydroxide](https://en.wikipedia.org/wiki/Sodium_hydroxide) (solubility about 1000 g per litre of water at 25 °C; dissolving it is highly exothermic) and [Potassium hydroxide](https://en.wikipedia.org/wiki/Potassium_hydroxide) (commercial samples about 90 % pure). - NIOSH Pocket Guide to Chemical Hazards: [Sodium hydroxide](https://www.cdc.gov/niosh/npg/npgd0565.html) and [Potassium hydroxide](https://www.cdc.gov/niosh/npg/npgd0523.html): incompatible materials (including aluminium, tin and zinc), symptoms and first aid. - Tata Chemicals, [Sodium hydroxide safety data sheet](https://www.tatachemicals.com/upload/images/sodium-hydroxide-tcl-sds-ghs-2021.pdf) (GHS, 2021): add sodium hydroxide to cold water with stirring, never water to sodium hydroxide. - Poison Control (National Capital Poison Center), [First aid for poisonings](https://www.poison.org/first-aid-for-poisonings): rinse skin for at least 15 minutes and eyes for 15 to 20 minutes; do not induce vomiting. - NHS, [Acid and chemical burns](https://www.nhs.uk/conditions/acid-and-chemical-burns/): rinse with running water for about an hour and put nothing else on the burn. - IFRA, [Standards library](https://ifrafragrance.org/standards-library): fragrance limits by product category; bar and liquid soap are category 9. ## More formula tools For lotions, bigger or smaller batches, and choosing oils. - [Lotion formula calculator](https://cloverradiance.beauty/lotion-formula-calculator/): Phases and percentages that add up to 100 %, grams for any batch, and your supplier's usage rates checked. - [Recipe batch scaler](https://cloverradiance.beauty/recipe-batch-scaler/): Paste any gram or percentage recipe and scale it to a new batch weight, rounded to what your scale can show. - [Oil properties chart](https://cloverradiance.beauty/oil-properties-chart/): SAP values, fatty acids, iodine and INS for 47 oils and butters, sortable and searchable. ## Recommended Two free services for the online side of a soapmaking hobby. Disposable email · no sign-up ### CleanTempMail Ingredient shops, craft fairs and online soap classes often want an email address before they send a discount code or a sample recipe. CleanTempMail gives you a free temporary inbox straight away, with no sign-up, a random or custom address on hundreds of domains, and messages deleted automatically after 3 days. Read the one email you wanted; your own inbox stays quiet. [Open a temporary inbox](https://cleantempmail.com/) Disposable cloud browser · free domain lookups ### WebTraceCheck About to order lye, butters or fragrance oils from a shop you have never used? WebTraceCheck's free DNS and domain lookup shows the details behind the shop's domain, and its disposable cloud browser opens unfamiliar links on an isolated desktop that is deleted after each session. Nothing to install, with free time every day. [Try WebTraceCheck](https://webtracecheck.com/) ## Questions **What is superfat, and how much should I use?** Superfat is the share of oil left over because the calculator deliberately uses less lye than the oils could take. It is a margin for SAP values that differ from batch to batch and for small weighing errors, and it leaves a little free oil in the bar. SoapCalc's default is 5 %. A much higher superfat gives a softer bar that can go rancid sooner, and 0 % leaves no margin at all. **Why should I check the recipe with a second calculator?** Any calculator can be given a typo, the wrong unit or the wrong oil, and a lye mistake is the one that matters most. Before you make a new recipe, enter the same oils and settings in a second, independent lye calculator and check that the lye amounts agree closely; small differences come from slightly different SAP tables. If they differ by more than that, find out why before you weigh any lye. **Why does KOH have a purity setting?** Potassium hydroxide is usually sold about 90 % pure; most of the rest is water and carbonate. SAP values assume pure KOH, so the calculator divides by the purity: at 90 % it weighs out about 11 % more. Use the figure on your supplier's label or certificate. Sodium hydroxide is sold much purer, so most soapmakers leave its purity at 100 %. **Lye concentration, water as % of oils or water : lye ratio: which should I use?** They describe the same water in different ways, and the results panel shows all three. A 33 % lye concentration means the lye makes up 33 % of the solution's weight, the same as a water : lye ratio of about 2 : 1. Water as a percentage of the oils ties the water to the oils instead of the lye, so the strength of the solution changes from recipe to recipe; that is why many soapmakers prefer one of the other two. **Can I use it for liquid soap?** Yes. Choose KOH, enter your KOH's purity and set the water for the paste stage. Liquid soap is usually cooked as a thick paste and diluted with more water afterwards; that dilution water is not part of this calculation. **Can I sell soap made with these recipes?** The calculator only does the arithmetic; selling is regulated. In Great Britain, cosmetic products, including soap for washing skin, need a safety assessment by a qualified safety assessor and a Responsible Person before they go on sale ([GOV.UK guidance](https://www.gov.uk/guidance/making-cosmetic-products-available-to-consumers-in-great-britain)), and the EU has similar rules. In the US, the FDA explains that true soap is regulated by the Consumer Product Safety Commission, while soap sold with cosmetic or drug claims falls under the FDA ([FDA soap FAQ](https://www.fda.gov/cosmetics/cosmetic-products/frequently-asked-questions-soap)). Check the rules where you sell.