Why jar size and wax weight are different numbers
This is the single thing that trips up every new candle maker. A jar is sold by the volume it holds. Wax is sold by weight. An 8 fl oz jar does not take 8 oz of wax, and a 300 ml jar does not take 300 g.
Wax is lighter than water. Soy sits at roughly 0.9 g per millilitre, so a space that would hold 300 g of water holds about 270 g of wax. Then you leave headspace, because pouring to the brim puts the wick at the rim and leaves nowhere for a lid. Take 10% off for that and the same jar wants about 243 g.
The calculation
Two multiplications, in this order, and nothing else:
wax weight = jar volume × fill level × wax density
Keeping fill level and density apart matters. Most calculators collapse both into a single factor of 0.86 and hand you one number. That factor silently assumes you are pouring soy to about 95% full. Change either of those things and it is wrong, which is why the answer above moves when you switch to beeswax.
Wax densities
Typical solid densities and the fragrance each wax will hold. Your supplier’s spec sheet always beats a general figure.
| Wax | Density (g/ml) | Max fragrance |
|---|---|---|
| Soy (container blend) | 0.9 | 10% |
| Coconut soy blend | 0.92 | 12% |
| Coconut apricot | 0.92 | 12% |
| Paraffin (container) | 0.9 | 10% |
| Paraffin (pillar) | 0.9 | 6% |
| Beeswax | 0.958 | 6% |
| Rapeseed (canola) blend | 0.92 | 10% |
| Palm | 0.9 | 10% |
| Gel wax | 0.95 | 5% |
Working it out for an unusual vessel
If the supplier has not printed a capacity, measure it. Fill the empty vessel with water to where you intend to pour, tip that water onto a scale, and read the grams. Water is 1 g per millilitre, so the number you see is the usable volume in millilitres — the fill level is already accounted for, so set fill to 100% and enter that figure directly.
Odd shapes and moulds
The water method works for anything: tapered glasses, teacups, silicone moulds, tins with a rolled lip. It is more reliable than geometry for anything that is not a straight-sided cylinder.
Common mistakes
- Measuring wax by volume. Flakes and pellets pack differently every time. Always weigh.
- Forgetting wastage. Wax clings to the pot and the jug. Melt about 5% more than the batch needs.
- Reusing a soy figure for beeswax. Beeswax is denser, so the same jar needs more of it by weight.
- Pouring to the brim. No headspace means no room for a lid and a wick sitting dangerously close to the rim.