This saponification value calculator works both ends of the SAP number: the lab determination (mg of KOH that saponify 1 g of fat, from titration data) and the soapmaker’s question — how much NaOH or KOH a given weight of oil actually needs.

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One Number From Lab Bench to Soap Pot

The saponification value is the milligrams of potassium hydroxide needed to completely saponify one gram of a fat or oil — a number that encodes the oil's average fatty-acid chain length (shorter chains mean more ester bonds per gram, hence a higher SV). It lives a double life. In the analytical lab it is measured by back-titration: reflux the sample with excess alcoholic KOH, titrate what's left, and compute SV = 56.1 × N × (V_blank − V_sample) ÷ W — the worked defaults give 56.1 × 0.5 × 8.9 ÷ 1.02 = 244.8 mg KOH/g, a palm-kernel/coconut-family figure. In the soapmaker's kitchen the same number runs forward: lye required = oil weight × SV, with a molar-mass conversion when the lye is NaOH instead of KOH (× 40.00/56.11 = 0.713). For a kilogram of coconut oil (SV ≈ 257): KOH = 257 g, or NaOH = 183.2 g — the origin of the "0.183 SAP value" (grams NaOH per gram oil) printed in soap charts, which is just SV wearing kitchen units: SAP(NaOH) = SV × 0.713 ÷ 1000. Every lye calculator on the internet is this page's arithmetic with a database of SVs behind it.

The craft caveats separate a number from a good bar. Superfatting: soapmakers deliberately under-lye by typically 5% (the calculator's default), leaving a margin of unsaponified oil for mildness and insurance against weighing error — liquid-soap makers using KOH often superfat lower (0–3%) because excess oil clouds the product. Purity: commercial NaOH and KOH are not 100% pure (KOH flakes commonly ~90%), and serious formulators divide by the purity fraction (needing MORE lye than the ideal figure); the calculator returns the chemically exact requirement for pure alkali — adjust for your product's assay. Variation: SV is a property of a biological material — coconut oil's published values span roughly 250–268 by origin and season — which is why the superfat margin exists and why a new oil from a new supplier deserves its published SV checked rather than assumed. Safety, stated plainly: lye is caustic, its dissolution is strongly exothermic, and it is always added to water, never the reverse; this page does the arithmetic, and your safety practice (gloves, goggles, ventilation, no aluminum) does the rest. Within those disciplines, the SV is a genuinely beautiful piece of applied stoichiometry: one titration constant from 19th-century fat chemistry still dosing every handmade bar on Earth.

Worked Examples (Verified)

  • Defaults (lye mode): 1,000 g oil, SV 257, 5% superfat → NaOH 174.1 g · KOH 244.1 g after discount (183.2 g / 257.0 g before).
  • Titration mode: 0.5 N, blank 24.8, sample 15.9 mL, 1.02 g → SV 244.8 mg KOH/g.
  • Olive oil batch: 500 g, SV 190, no superfat → KOH 95.0 g · NaOH 67.7 g.
  • Castor blend check: 200 g castor, SV 180 → KOH 36.0 g · NaOH 25.7 g.

Saponification Discipline

  • SV is defined with KOH regardless of your lye — NaOH figures always pass through the 40/56.11 molar-mass conversion.
  • Use the SV for YOUR oil and supplier; published tables are ranges, and blends need the weight-weighted average SV of the components.
  • Superfat is a discount on LYE, computed after the stoichiometric amount — and it presumes the SV was right.
  • Correct for lye purity in precision work (especially KOH ≈ 90%): divide the pure-alkali requirement by the purity fraction.
  • Titration mode: the blank is not optional bookkeeping — it absorbs the reagent's own alkali consumption and endpoint drift.

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Frequently Asked Questions

What is saponification value?

The milligrams of potassium hydroxide required to saponify (fully hydrolyse the esters of) one gram of a fat or oil. It inversely reflects average fatty-acid chain length: short-chain fats (coconut ≈ 257, palm kernel ≈ 245) top the scale; long-chain oils (olive ≈ 190, castor ≈ 180) sit lower, because a gram of short-chain oil contains more ester bonds to cleave. The value is defined with KOH by convention even when the actual soap is made with NaOH — conversion is a fixed molar-mass ratio, handled by this calculator in both its modes.

How is saponification value calculated from titration?

SV = 56.1 × N × (V_blank − V_sample) ÷ W, where N is the titrating acid's normality, the V's are blank and sample titration volumes in mL, W is sample weight in grams, and 56.1 is the mg weight of one milliequivalent of KOH. The method refluxes the oil with a known excess of alcoholic KOH, then back-titrates the unconsumed alkali; the blank corrects for the reagents themselves. This calculator's titration mode implements the standard formula — with the worked example (0.5 N, 8.9 mL difference, 1.02 g) returning 244.8.

How much NaOH do I need for 1 kg of coconut oil?

Coconut oil's SV ≈ 257 mg KOH/g, so 1,000 g needs 257 g of KOH-equivalent alkali — as NaOH that's 257 × (40.00/56.11) = 183.2 g at zero superfat, or about 174 g with the customary 5% superfat discount (both figures computed live in the calculator's default view). In "SAP value" language, coconut's NaOH SAP is 0.183 g per gram of oil. Always confirm the SV for your specific oil — published coconut values range roughly 250–268 — and apply your lye's purity if formulating precisely.

What is the difference between SAP value and saponification value?

Soapmaking "SAP value" is the saponification value re-expressed for the kitchen: grams of a SPECIFIC lye per gram of oil. Saponification value (mg KOH/g) is the lab constant; SAP(NaOH) = SV × 0.713 ÷ 1000 and SAP(KOH) = SV ÷ 1000. So coconut's SV 257 becomes SAP(NaOH) 0.183 and SAP(KOH) 0.257. Confusion between the two — using an NaOH SAP chart figure as if it were an SV, or vice versa — is a classic cause of lye-heavy or greasy failed batches; the calculator keeps both lyes' outputs visible side by side to prevent it.

Why do soapmakers superfat?

Superfatting means adding less lye than stoichiometry demands (typically 5% less for bar soap), leaving a small fraction of the oils unsaponified. It serves two purposes: mildness (the free oils make the bar feel conditioning, and guarantee no caustic excess survives), and insurance (it absorbs errors in weighing, SV table variation, and lye purity). The trade-off is shelf life and lather at high superfats (excess unsaturated oils can go rancid — "dreaded orange spots"). The calculator applies the discount to the lye figure; the percentage is a formulation choice, not a fudge factor.

Does the type of lye change the soap?

Yes — the cation shapes the product. NaOH gives hard, long-lasting bar soaps (sodium soaps are firm and less soluble). KOH gives soft/paste and liquid soaps (potassium soaps are more soluble and stay pourable) — which is why liquid soapmaking is KOH territory and why its SV arithmetic matters despite KOH's ~90% commercial purity. Dual-lye formulations exist for shaving soaps (hard puck + rich stable lather): the calculator's side-by-side NaOH/KOH outputs make splitting a batch between the two a simple proportion.

Why does my oil's SV differ between sources?

Because oils are agricultural products, not reagents. SV depends on the fatty-acid profile, which shifts with cultivar, climate, harvest and refining; two honest tables can list olive oil at 184 and 196. Industrial users titrate each lot (the calculator's second mode); home soapmakers rely on reputable supplier values for their actual oil and let the superfat margin absorb the residual uncertainty. For blends, compute the weight-weighted average of the component SVs — the calculator handles one oil at a time, and blend SVs are linear in the mass fractions.

Is this saponification value calculator free?

Yes — free, instant, no sign-up. Get lye amounts from an SV and oil weight (with superfat), or determine an SV from titration data. Educational only — follow proper caustic-safety practice when handling lye.