Liquid Soap Calculator — KOH & Liquid Soap Lye Math

A liquid soap calculator (or KOH calculator) estimates how much potassium hydroxide and initial water belong to your oil blend at a chosen superfat and water ratio. It answers the paste-stage alkali question—not bottle dilution, viscosity, or preservatives. Think “first cook,” not “finished shower gel.”

Potassium salts stay softer and more soluble in water-heavy systems, which is why body washes and pastes use KOH. The numbers are not interchangeable with bar soap. Keep NaOH tools like the soap calculator mentally separate so you never open the wrong bag beside the scale.

For each oil: partial_KOH ≈ grams × KOH_SAP. Sum, then multiply by (1 − superfat%). Water ≈ KOH × ratio for the first solution line. Compare to a second table—disagreements usually trace to SAP source or conversion factor.

Thick paste for dilution later: Log cook water separately from dilution water. Castile-style blends: Expect long cook; clarity builds over stages. Split oils: Coconut-heavy for lather, olive for story—balance with skin testing, not only numbers.

• Using NaOH SAP directly — wrong alkali.
• Ignoring hygroscopic KOH storage — strength drifts.
• Skipping pH and dilution notes on the card.
• Confusing this water line with all water ever added.

Label jars “KOH only.” Track paste weight before dilution for concentration math. Pair fatty acid goals with SAP value documentation when you publish recipes.

Liquid soap is usually made with potassium hydroxide so the soap stays softer and dilutes into paste or clear soap. NaOH bar factors do not belong here—if you see “0.135” for olive in a NaOH table, the KOH number is higher per gram of oil. Our KOH calculator applies a conversion from the NaOH SAP list so you can stay in one oil menu; purists may replace values with exact KOH SAP columns from their supplier.

Most searches here boil down to: how much KOH for this oil blend at this superfat, and how much water for the first cook? This tool answers the alkali side; dilution water later is a separate line in many workflows. For full bar-formula math (NaOH), use the soap calculator.

KOH (potassium hydroxide) is the alkali used for liquid and soft soaps. It has different molecular weight than NaOH, so SAP tables list different factors. In SoapLab we derive approximate KOH SAP from NaOH SAP × 1.4028—a common teaching shortcut—then run the same Σ(weight × SAP) × (1 − superfat%) structure as bar soap math.

If your KOH soap calculator online result disagrees slightly with Soap Guild references, check whether their table used a different SAP source or purity assumption.

Build your oil list with purpose: coconut and palm kernel for lather, olive or other soft oils for mildness, and small amounts of castor for clarity helpers in some formulas. Enter grams, read KOH before and after superfat, and compare to a second tool before production.

Paste cooks, crock pots, and dilution ratios change viscosity and preservation needs—those are not modeled here. Pair numeric output with pH strips or lab tests if you sell finished liquid soap.

When you also make bars, bookmark the soap calculator and lye calculator for NaOH workflows so you never grab the wrong alkali bag.

Solid KOH numbers are only the first line in your batch record. Track cook time, dilution water added later, fragrance solubility, and preservative choice. Regulators and insurers often want traceability—your numbers should tie to ingredient lots.

For scaling paste size, use recipe scaling once percentages are stable. For water discipline in bars, the water ratio calculator complements this page’s lye-side estimate.

Scenario: 900 g total oils: 60% coconut (540 g), 40% olive (360 g). Superfat 3% (common teaching starting point for liquid), water ratio 2.5 on the KOH line.

Step 1 — Read KOH: The tool uses KOH SAP derived from NaOH SAP × 1.4028 per oil; compare the total to a dedicated KOH table if your supplier publishes one.

Step 2 — Cook mindset: The water shown is for initial solution and early cook planning—not the dilution water you may add weeks later when thinning to bottle viscosity.

Step 3 — Bar soap reminder: If you also run NaOH batches, keep the soap calculator printouts in a different folder so bags never cross.

KOH grams from SAP answer saponification stoichiometry; they do not guarantee clear dilutable soap. Clarity depends on oil choice, cook protocol, dilution order, sequestering agents, and sometimes pH adjustment—log those steps separately.

If you sell liquid soap, plan pH testing and preservative strategy with qualified guidance. This page stays an educational KOH calculator layer, not a regulatory sign-off.

Understand how KOH and NaOH fit the “lye” conversation and see how liquid soap compares to other beginner paths in our overview of how to make soap.