Cold Process Soap Calculator

Cold process soap making is as much science as art. The Cold Process Soap Calculator is a must-have tool for hobbyists and small-batch artisans: it turns your oil recipe, superfat percentage, and water choice into the exact grams of NaOH (lye) and water you need, plus helpful notes on cure time, additives, and safety.

Cold Process Soap Calculator

Saponification values (NaOH): Olive: 0.135, Coconut: 0.183, Palm: 0.141, Castor: 0.128, Sunflower: 0.135, Shea: 0.128

How the Cold Process Soap Calculator Works

At its core, a cold process soap calculator converts the weight of each oil/fat in your recipe into the amount of sodium hydroxide (NaOH) required to saponify (turn into soap) those oils. Then it adjusts that lye amount for your chosen superfat (free oils left unsaponified for moisturizing), and computes the water needed based on your chosen water concentration.

Inputs the calculator accepts:

  • List of oils/butters with weights (g or oz)
  • Desired superfat percentage (commonly 0–8%)
  • Water as a % of total oils (commonly 25–40%)
  • Optional: replace NaOH with KOH (liquid soap) — needs different SAP values
  • Optionally show totals per loaf, per bar, or batch scaling

Outputs you get:

  • Total NaOH (grams or ounces) required (adjusted for superfat)
  • Water amount (grams/ounces)
  • Water : NaOH ratio
  • Total soap batter weight
  • Optional: suggested cure time, notes about trace, and additives

The Formulas (plain text & simple)

  1. NaOH required for each oil (g):
    NaOH_oil_g = Oil_weight_g × SAP_value (NaOH per g oil)
  2. Total NaOH (before superfat):
    Total_NaOH = sum(NaOH_oil_g for all oils)
  3. Adjust for superfat:
    Final_NaOH = Total_NaOH × (1 - Superfat_decimal)
    (Example: 5% superfat → multiply by 0.95)
  4. Water amount (user-chosen % of oils):
    Water_g = Total_Oils_g × Water_percent
  5. Water:lye ratio:
    Ratio = Water_g / Final_NaOH_g
  6. Total batch weight:
    Total_Soap = Total_Oils_g + Water_g + Final_NaOH_g
    (Note: soap chemistry slightly changes mass as saponification proceeds; this is for batching)

Common SAP (NaOH) Values — typical reference table

SAP values vary by source. Treat these as commonly used averages; always verify for production with a trusted lye table.

  • Olive oil (extra virgin) — 0.134 g NaOH / g oil
  • Coconut oil (refined) — 0.183
  • Palm oil — 0.144
  • Shea butter — 0.128
  • Cocoa butter — 0.137
  • Castor oil — 0.128
  • Sweet almond oil — 0.136
  • Sunflower oil — 0.136
  • Avocado oil — 0.135

(These numbers mean: e.g., 1 g coconut oil needs ~0.183 g NaOH to saponify.)

Worked Example (step-by-step)

Recipe (weights in grams):

  • Olive oil: 400 g
  • Coconut oil: 300 g
  • Palm oil: 300 g
  • Total oils = 1,000 g

Assumed SAP values (from table):

  • Olive 0.134, Coconut 0.183, Palm 0.144

Choose: Superfat 5% (0.05) and Water 38% of oils.

  1. Calculate NaOH per oil:
    • Olive: 400 × 0.134 = 53.6 g NaOH
    • Coconut: 300 × 0.183 = 54.9 g NaOH
    • Palm: 300 × 0.144 = 43.2 g NaOH
  2. Total NaOH before superfat:
    53.6 + 54.9 + 43.2 = 151.7 g
  3. Apply 5% superfat:
    Final NaOH = 151.7 × (1 − 0.05) = 144.1 g (rounded)
  4. Water (38% of oils):
    Water = 1000 × 0.38 = 380 g
  5. Water : NaOH ratio ≈ 380 / 144.1 ≈ 2.64 : 1

Result: For this 1 kg oil recipe at 5% superfat and 38% water, use ~144.1 g NaOH and 380 g water.

(If you prefer ounces: convert after calculation — 1 g = 0.035274 oz.)

Safety, Practical Notes & Best Practices

  • Safety first: NaOH is caustic. Always wear gloves, eye protection, long sleeves, and work in a ventilated area. Add lye to water — never water to lye. Have vinegar and running water available for spills/skin contact (vinegar neutralizes lye on skin surface).
  • Verify SAP values: Different suppliers and refinements change SAP slightly. Use the exact SAP values from your oil supplier or a trusted lye table for commercial batches.
  • Superfat choice: 0–2% for cleansing bars (less conditioning), 4–8% for moisturizing bars. Higher superfats leave more free oil but reduce lather/cleaning.
  • Water discount: Lower water (e.g., 28–32%) yields faster trace and shorter cure times but works faster; higher water (35–40%) gives more time to work with designs.
  • Trace & cure: Cold process typically reaches trace (stirring) then you pour into molds. Cure bars on racks 4–6 weeks for full hardness and milder pH.
  • Fragrances & additives: Add fragrance (EO or FO), colorants, exfoliants at recommended percentages; they do not affect lye calculation but may affect trace and stability.
  • Test small batches: When changing oils or additives, do a small test batch before scaling.

Troubleshooting & Common Scenarios

  • If batter thickens too fast → lower coconut/palm content or lower water content.
  • If bars are too soft after cure → increase harder oils (coconut/palm) or extend cure time.
  • If too harsh → increase superfat slightly or reduce coconut content.

20 Frequently Asked Questions (FAQs)

  1. What is a cold process soap calculator?
    A tool that computes the precise lye and water needed for a cold process recipe based on oils, superfat, and water percent.
  2. Why do I need a calculator?
    Because every oil has a different saponification (SAP) value — manual math is error-prone and dangerous.
  3. What is superfat?
    The percentage of free oils left unsaponified to add conditioning and avoid dryness.
  4. How accurate are SAP values?
    They’re approximations; use supplier-specific SAP values for production-level accuracy.
  5. What water percentage should I use?
    Commonly 30–38% of total oils. Lower % = faster trace and harder bars; higher % = more workable batter.
  6. Can I use KOH values for liquid soap?
    Yes, but KOH has different SAP values — the calculator must be set for KOH.
  7. How to convert grams to ounces?
    Multiply grams by 0.035274 to get ounces.
  8. Is NaOH the same as lye?
    Yes — sodium hydroxide is commonly called lye in soapmaking.
  9. Do additives change lye amount?
    No — colorants, fragrances, and exfoliants do not change lye; only oils/fats do.
  10. What is water:lye ratio?
    It’s water weight divided by lye weight; helps predict trace behavior.
  11. How long to cure soap?
    Typically 4–6 weeks for cold process; some recipes benefit from longer.
  12. Do I need a scale?
    Absolutely — use a digital scale accurate to 0.1 g for safety and consistency.
  13. How to scale a recipe?
    Multiply each oil, water, and calculated lye by your scale factor — or use the calculator’s batch-scaling feature.
  14. Can I use the calculator for melt-and-pour?
    No — melt-and-pour soap is pre-saponified and does not require lye.
  15. What about palm-free recipes?
    Replace palm with other harder oils (coconut, cocoa butter) but re-check SAP and properties.
  16. Are essential oils safe in cold process?
    Many are; check recommended usage rates and stability at high pH.
  17. Why test pH after cure?
    To ensure safe skin pH (typically 8–10 for well-cured soap).
  18. Can I reuse lye solution?
    No — prepare fresh for each batch. Lye solution concentration must be accurate.
  19. What happens if I add too little lye?
    The batch is over-superfatted — will have excess oils and may spoil over time.
  20. What if I add too much lye?
    The soap will be caustic and unsafe for skin — discard or rebatch carefully.

Final notes

A good Cold Process Soap Calculator is essential for consistent, safe, and reproducible soapmaking. Add a clear safety block, allow users to choose units, include supplier SAP overrides, and provide a printable recipe sheet with lye safety reminders. If you’d like, I can produce ready-to-paste content for your tool UI (short help pop-ups, safety checklist, or a downloadable recipe card) — tell me which one you want and I’ll create it.