Lye Masterbatch Calculator
Many soapers pre-dissolve lye into a 50% masterbatch solution — equal weights of dry lye and distilled water — so they can skip handling dry lye on every soap day. This tool tells you how to mix a batch, and how much of it to weigh out for any recipe.
A. Make a Masterbatch
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Dry NaOH lye
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Distilled water
- Weigh the distilled water into a heat-safe, lye-safe container (HDPE #2 plastic or stainless steel — never aluminum or glass).
- Slowly pour the weighed dry lye into the water (never the reverse), stirring gently until fully dissolved.
- Let it cool completely — the solution heats itself to around 180°F.
- Pour into a sealable HDPE #2 container, label it “CAUSTIC — 50% LYE SOLUTION” with the date, and store sealed.
B. Use Masterbatch in a Recipe
Take the lye and water weights from any lye calculator recipe and enter them here. We’ll tell you how much 50% solution to weigh, plus the extra water to add.
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50% solution to weigh
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Extra distilled water
Safety: A 50% masterbatch is just as caustic as fresh lye solution — goggles and gloves every time you open it. Label the container “CAUSTIC — 50% LYE SOLUTION” with the date. Keep it sealed, away from children and pets. Do not store in aluminum or glass long-term — use HDPE #2 plastic.
Why it works: a 50% solution is half lye by weight, so weighing out 2 × your recipe’s lye weight in solution gives you exactly the right amount of lye — plus half your water is already in there. The rest of the recipe’s water gets added separately.
