🧼 Soap Lye Calculator

Calculate lye (NaOH for bar soap, KOH for liquid soap) and water amounts for cold-process soapmaking. Add multiple oils with different saponification values.

Soap type

KOH purity (if applicable)

Superfat / lye discount (%)

Water as % of oil weight

Oil Blend

Common Soap Oils

🫒 Olive Oil

SAP (NaOH): 0.134. Conditioning, skin-loving. Slow to trace. Produces soft bars — best blended with coconut oil. Max 70–80% for bar soap.

🥥 Coconut Oil

SAP (NaOH): 0.190. High cleansing and lather. Hard bar. Drying at >30% — limit to 20–30% in skin-safe soap. Increases shelf life.

🌴 Palm Oil

SAP (NaOH): 0.141. Adds hardness and stable lather. Can replace up to 30% of oil. Sustainability concerns — consider RSPO certified.

🌻 Sunflower Oil

SAP (NaOH): 0.134. Conditioning, high oleic. Similar to olive oil. Shorter shelf life — use up to 15%. Good for sensitive skin.

🏃 Castor Oil

SAP (NaOH): 0.128. Boosts and stabilises lather. Only 5–8% needed — too much makes sticky soap. Always include in formulas.

🌿 Shea Butter

SAP (NaOH): 0.128. Very conditioning and creamy. 5–15% adds luxury. Reduces lather slightly. Pairs well with coconut oil.

🫧 Lard / Tallow

SAP (NaOH): 0.138–0.140. Produces hard, long-lasting bars with creamy lather. Traditional soapmaking staple. Very stable shelf life.

🌸 Sweet Almond Oil

SAP (NaOH): 0.136. Gentle and conditioning. Good for facial and baby soaps. Use up to 20% for skin benefits.

⚠️ Safety first: Lye (sodium or potassium hydroxide) is highly caustic. Always add lye TO water, never water to lye — it can splatter dangerously. Wear goggles, gloves, and work in a well-ventilated area. The lye solution heats dramatically on mixing. Keep vinegar nearby to neutralise spills.

🧪 Superfat: A 5% superfat means 5% of the oils remain unsaponified (not converted to soap). This leaves a margin of free oil that moisturises and reduces the risk of a lye-heavy batch. Never go below 0% superfat in skin-use soap. 5–8% is the sweet spot for most recipes.

⏰ Cold process timeline: Mix → trace → pour → gel phase (24h insulated) → unmold (24–48h) → cure (4–6 weeks). Soap is safe to use after full cure when excess water has evaporated and saponification is complete. Test with pH strips — soap pH should be 8–10.