Free tool

Free during beta

Free soap lye calculator for Canadian makers

Build a cold-process bar soap or liquid soap recipe using NaOH or KOH. Enter oils, superfat, lye purity, and water method to calculate batch weights plus live hardness, cleansing, conditioning, bubbly, and creamy scores.

Soap calculators are starting points, not safety reviews

FormulaNorth helps organize cosmetic formulation, label, costing, and CNF preparation information. It is not legal or regulatory advice and does not replace Health Canada guidance, professional regulatory review, or the maker's responsibility to verify product compliance before sale.

📚 Free recipe library

15 trustworthy recipes — Castile, salt bar, milk soap, liquid, shave bar — open in calculator with one click.

🧪 SAP values chart

Compare NaOH and KOH values, iodine, and soap qualities for every oil in the calculator.

🧰 Starter kit guide

Equipment, safety gear, ingredients, and Canadian suppliers for your first batch.

🪜 CP step-by-step

Full first-batch walkthrough — from weighing to cure.

Preset

Batch and lye

Total oil weight

Lye type

NaOHKOH

Lye purity %

99 for food-grade NaOH; 90 for commercial KOH.

Superfat %

5–8% typical. Salt bars often 20%.

Fragrance / EO %

3–6% of oil weight is typical. Check IFRA limits.

Water

Water as % of oilsLye concentration %Water:lye ratio

% of oils

33–38% typical

OilsTotal: 100.0%

Additives (optional)

Transparent calculation

How this soap calculator determines lye and water

Each oil weight is multiplied by its NaOH or KOH SAP value. The results are added, reduced by the selected superfat, and adjusted for the purity of your lye. Water is then calculated using the method you selected: lye concentration, water-to-lye ratio, or water as a percentage of oils.

1. Choose the alkali

Use NaOH for hard bar soap or KOH for liquid and soft soap.

2. Verify the inputs

Confirm oil weights, SAP values, lye purity, superfat, and water method.

3. Assess the batch

Treat quality scores as comparisons, then document and evaluate the finished soap.

Review the complete SAP values chart →Download the soap batch record template (CSV) ↓Read the CCOHS sodium hydroxide safety profile →

The batch record is an editable production log for your formula inputs, lye calculation, process checks, cure observations, and release notes. It is a recordkeeping aid, not a substitute for your own safety review or regulatory obligations.

Frequently asked questions

Is the soap calculator free?

Yes. No account needed. Save your recipes inside FormulaNorth by creating a free account if you want version history and label drafting.

What does superfat mean?

Superfat is the percentage of oils intentionally left unsaponified — the calculator reduces lye by that percentage so some oils stay free for moisturizing. 5–8% is typical for bar soap.

Is the SAP data accurate?

The calculator uses working averages compared against established soap-making references. Natural oils and lye purity vary, so cross-check critical values against your supplier's specification sheet and Safety Data Sheet before production.

Should I use NaOH or KOH?

NaOH (sodium hydroxide) makes hard bar soap. KOH (potassium hydroxide) makes liquid or cream soap. Pick the lye type matching the product you're aiming for — the calculator switches the SAP values automatically.

What's a safe water-to-oil ratio?

There is no universally safe ratio for every formula. Water can be set as a percentage of oils, a water-to-lye ratio, or a lye concentration. FormulaNorth starts at 33% water as a percentage of oils, but makers should use a tested process and understand how less water can accelerate trace.

Is the soap I make ready to sell in Canada?

Health Canada lists soaps among cosmetics when they are represented for cosmetic uses such as cleansing. Cosmetics sold in Canada must meet notification, safety, ingredient, and labelling requirements; therapeutic claims or certain ingredients can change classification. Review your exact product before sale.

What are INS and Iodine values?

INS combines hardness and iodine to estimate overall soap quality (target ≈ 136–170). Iodine value indicates how unsaturated the oils are; lower is more shelf-stable (≤ 70 ideal for hard bars). Both are estimates — your final bar's longevity depends on cure, storage, and antioxidants.