Candles & melts

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.
• Flash point is the lowest temperature at which a liquid gives off enough vapour to form an ignitable mixture with air near its surface, and it is what flammable-liquid classes are drawn on: US DOT 49 CFR 173.120 (Class 3 at 60 °C or below; combustible liquid above 60 °C and below 93 °C) and OSHA 29 CFR 1910.1200 Appendix B.6 (categories 1–4, up to 93 °C). It does not set the temperature fragrance goes into wax at. CandleScience, “What temperature should I add fragrance oil to melted wax?” (updated 2026-05-04): add it “between 180-190°F (82-88°C) … regardless of the flashpoint of the fragrance oil”; and “What does the fragrance flashpoint mean?” (updated 2026-05-01): adding it above the flash point “will not cause it to combust”, the figure decides how it may be shipped, and scent added and poured soon “will not lose strength”. Cargill, NatureWax C-3 and C-6 handling sheet (11/16): melt at 160–200 °F (71.1–93.3 °C) and add the fragrance once the wax is completely liquid, with no flash-point condition. — The flash point still describes vapour that a flame or a spark can light, which is why hot wax is melted away from open flames and sparks whatever the oil. Follow your wax maker’s add temperature.
• 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.