Batchwell

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Lye and scent load calculators

Two calculators that work with your own recipes: one for soap, one for fragrance and essential oil in candles and body care.

Find it More → Calculators

Steps

  1. Go to More → Calculators.
  2. Choose NaOH · bar soap or KOH · liquid soap.
  3. Pick your oils and enter their grams. To work in percents, tick Enter oils as % of the oils and enter the Total oils (g). Tap Add oil for more.
  4. Set the Superfat (%). 5% is a common start.
  5. Choose Water by: Lye concentration (%), Water : lye ratio or Water as % of oils, and set its value.
  6. For KOH, check the KOH purity (%). Most KOH sold for soap is about 90%.
  7. Read the lye and water to weigh, the batch weight before additives, the lye concentration and the water to lye ratio.

Check a saved soap recipe

On a soap recipe, tap Check the lye, or choose it under Check one of your soap recipes. Batchwell loads the oils and shows the recipe’s real superfat. A negative number means more lye than the oils can use: check the recipe before you make it. Anything it doesn’t recognise as an oil is listed, so you can add it.

Scent load

  1. Enter the Batch weight (g): the wax for candles, the whole batch for body care.
  2. Enter Scent at (%) to see the grams, or Or: I used (g) to see the percent.

On a recipe, Check in calculators fills in that recipe’s scent percent and batch size.

Good to know

  • Lye is worked out oil by oil: its weight × its SAP value × (1 − superfat). KOH needs about 1.4 times as much as NaOH, divided by its purity.
  • The starting values are 33% lye concentration, a 2 : 1 water to lye ratio, or water at 38% of oils.
  • SAP values are published averages. Real oils vary a few percent, which the superfat covers.
  • Add lye to water, never water to lye, and wear goggles and gloves. Double-check a new recipe in a second calculator before the first batch.
  • The safe top scent rate depends on the oil and the product. Check the IFRA certificate or your supplier’s maximum, and your wax’s own maximum load.

Written for the Batchwell beta, October 2026. Screens can change as we build; if something here doesn’t match what you see, tell us.