Free Lye Calculator

Calculate the exact amount of NaOH (sodium hydroxide) or KOH (potassium hydroxide) needed for your cold process, hot process, or liquid soap recipe. Choose from 20 common soapmaking oils, adjust your superfat and water amounts, and get an instant recipe summary you can take to the soap pot.

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Recipe Setup

Typical: 3–8%. Higher = more skin-conditioning, softer bar.
Default 38% of oil weight. Typical range 25–38%.

Oils & Fats

Enter the weight of each oil in your recipe. Leave blank or 0 to skip.

Results

Lye Needed
0.00g
Water Needed
0.00g
Total Oils
0.00g
Total Batch
0.00g
Water : Lye Ratio
—

Recipe Summary

Add at least one oil weight to see your recipe.
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How the Lye Calculator Works

Each oil has a known saponification value (SAP) — the amount of lye required to fully saponify 1 gram of that oil. The calculator multiplies each oil's weight by its SAP value, sums the totals, then reduces the lye amount by your chosen superfat percentage so a portion of the oil remains un-saponified for a more conditioning bar.

For liquid soap (KOH), we apply the molecular-weight ratio of potassium hydroxide to sodium hydroxide (≈1.4025) and adjust for KOH purity, since flakes are typically only 90% pure.

Safety note: Lye is caustic. Always wear gloves and eye protection, add lye to water (never the reverse), and verify your recipe with a second source before mixing.