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Calculators

Candles & melts

Ask a chandler for a ten per cent load and they mean ten grams of fragrance per hundred grams of wax. Ask a cosmetic formulator and they mean ten per cent of the finished candle, which for the same jar is 9.09 %. Type whichever one you were given; this shows both.

The wax
Defaults for the family. Your grade’s own data sheet beats them — Golden Wax 464 and Nature Wax C-3 are both "soy" and take different loads.
Your vessels
Fill it with water and weigh it: one gram is one millilitre.
Never to the brim: the wick tab and the headspace both take room. Most jar candles sit near 85 %.
The fragrance
Flash point
From its safety data sheet. Leave it blank if you do not have one.

fill in the vessel and the load

Calculated at soapformulator.com, every value sourced. Check the figures against your own scale.

The formula, and where it comes from 
wax       = V × ρ_solid × fill × vessels     # ρ solid, not molten

of wax:   fragrance = wax × load ÷ 100
of total: fragrance = wax × load ÷ (100 − load)   # it is part of its own total

load of wax   = fragrance ÷ wax × 100
load of total = fragrance ÷ (wax + fragrance + additives) × 100
  • Wax manufacturers state maximum fragrance load as a percentage of wax weight: fragrance = wax × load ÷ 100. Expressed as a percentage of the finished candle the same load is fragrance ÷ (wax + fragrance) × 100. — The two conventions differ by roughly a tenth of the load. Always check which one a supplier figure is quoted in.
  • Solid paraffin and vegetable waxes have densities around 0.90–0.96 g/mL; molten, around 0.77–0.82 g/mL. A vessel measured by filling it with water gives its volume, which must be multiplied by the solid density to give the wax it holds. — Manufacturers publish a density per grade; use theirs where you have it. The defaults here are a starting point.
  • The flash point on a fragrance oil’s safety data sheet is the lowest temperature at which its vapour forms an ignitable mixture. Adding fragrance to wax above that temperature risks ignition and drives off the volatiles that carry the scent.
  • Cure is the time between pouring and burning, during which the fragrance binds into the wax matrix. Soy and coconut waxes are conventionally cured 1–2 weeks, paraffin 24–48 hours. — A convention of the craft. There is no published measurement that fixes a cure time for a given wax.

Why wax is weighed and vessels are not

A vessel has a volume and wax is bought by weight, so the two need a density between them. Solid wax is around 0.9 g/mL and molten wax nearer 0.78; using the molten figure against a vessel measured with water short-pours every jar by about a seventh.

Cure

The time between pouring and burning, while the fragrance binds into the wax. Soy and coconut are conventionally given one to two weeks, paraffin a day or two. There is no measurement behind those numbers — they are what the craft has settled on.

Common questions

Which convention does my supplier mean?
A wax manufacturer quoting a maximum load almost always means percent of wax. A fragrance house quoting an IFRA limit always means percent of the finished product. When a shop just says "10 %", assume wax and check.
Can I just add more fragrance?
Past what the wax holds it does not dissolve, it sits. You get oily patches on the top, a ring around the wick, a bigger flame and sometimes no more scent at all, because the fragrance that never bound into the wax never evaporates from the melt pool either.
Does the flash point matter at pouring temperature?
It matters when you add the fragrance, not when you pour. Above the flash point the vapour can ignite, and short of that you are driving off the volatiles that carry the scent. Let the wax down below it first.
Is there an IFRA limit for candles?
Yes — category 12, for products with no skin contact. It is usually generous, but it is not absent, and it is stated as a percentage of the finished candle rather than of the wax.

Goes well with

All tools
Fragrance & allergen check IFRA load by product type and EU/Canada allergen declarations from supplier sheets
Formulas & sources The exact equations behind every result, with citations

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