Sizu Home › Calculators › Scent and Allergen Checker
Opens on the book's Market Batch. Change any number to your own and press Calculate.
Allergens from your safety data sheet: each one's % in the oil (the book's example figures)
Enter the batch and press Calculate.
The formula
- Scent at % of oils = oils × rate. At % of the whole batch = (oils + lye + water) × rate ÷ (1 − rate)
- Scent as % of the batch = scent ÷ (oils + lye + water + scent)
- The certificate's maximum is a % of the finished product: the lower of your rate and its cap wins
- Allergen in the soap = scent % of the batch × the allergen's % in the oil (from the SDS). Declare it above 0.01 % in rinse-off products (EU, UK)
The book's worked example, Chapter 6. The Market Batch: 3 % of 960 g of oils = 28.8 g of lavender, which is 2.07 % of the 1,390.6 g batch. If the oil's sheet listed linalool at 30 %, the soap would hold 2.071 % × 0.3 = 0.62 %, about 62 times the 0.01 % line: it goes on an EU or UK label.
Essential oils are not safe because they are natural: some are skin sensitizers. The allergen figures here are the book's examples; use the ones on your own oil's safety data sheet and certificate. Prices are illustrative US supplier prices from October 2026, shown without a currency sign; put in your own. Everything stays in your browser: no sign-up, nothing stored.