Wax weight from volume: specific gravity and the ounce problem
A candle jar is sold by volume, but wax is bought and weighed. To go from one to the other you need the specific gravity of the wax: its weight compared with the same volume of water. Water is the reference, so a wax with a specific gravity below one is lighter than water.
The weight of a fill is the volume you pour times the specific gravity. Published figures are about 0.9 for soy wax flakes (a supplier's safety data sheet), around 900 kilograms per cubic metre for paraffin, and about 0.97 for white beeswax at room temperature. They are typical values: for an exact figure use your own supplier's data sheet. No citable figure was found for coconut or blended waxes, so those are entered as a custom gravity.
A fluid ounce measures volume and an ounce measures weight. A jar that holds eight fluid ounces of water holds a little more than eight ounces of water by weight, and a wax lighter than water weighs less than that, so the number on the jar is not the weight of wax it takes. To avoid the question, fill the jar with water to the level you will pour to and weigh the water: the calculator's water weight mode takes that figure directly.
A blend of waxes is treated as if the volumes of its parts add up. Its specific gravity is one divided by the sum of each wax's share over its own gravity, which always lies between the lightest and the heaviest wax in the mix. Dividing the batch weight by that gravity gives the volume, and dividing the volume by the jar size gives the number of jars.
Chart: soy wax per candle by jar size and fragrance load
Each cell is the wax for one candle filled to the rim with soy wax. The column is the fragrance load; the oil is part of the same fill, so more oil means less wax.
| Fragrance percentage | ||||
|---|---|---|---|---|
| Jar volume | 0 % | 6 % | 8 % | 10 % |
| 4 US fl oz | 106.46 g | 100.44 g | 98.58 g | 96.79 g |
| 6 US fl oz | 159.70 g | 150.66 g | 147.87 g | 145.18 g |
| 8 US fl oz | 212.93 g | 200.88 g | 197.16 g | 193.57 g |
| 9 US fl oz | 239.55 g | 225.99 g | 221.80 g | 217.77 g |
| 12 US fl oz | 319.39 g | 301.32 g | 295.74 g | 290.36 g |
| 16 US fl oz | 425.86 g | 401.75 g | 394.31 g | 387.14 g |
Chart: fill weight by jar size and specific gravity
Each cell is the full weight of wax in one jar filled to the rim, with no fragrance. The same jar takes a different weight of each wax; read down to your jar size and across to your wax's gravity.
| Specific gravity | ||||
|---|---|---|---|---|
| Jar volume | 0.86 g/mL | 0.9 g/mL | 0.95 g/mL | 0.97 g/mL |
| 4 US fl oz | 101.73 g | 106.46 g | 112.38 g | 114.75 g |
| 8 US fl oz | 203.47 g | 212.93 g | 224.76 g | 229.49 g |
| 12 US fl oz | 305.20 g | 319.39 g | 337.14 g | 344.24 g |
| 16 US fl oz | 406.93 g | 425.86 g | 449.52 g | 458.98 g |
Used by
- Candle wax calculatorWax and fragrance oil for one candle jar or a whole batch.
- Candle wax blend calculatorWeight of each wax in a candle wax blend, the blend's gravity and the jars it fills.
Sources
- Candlemaking (Australia) safety data sheet, soy wax flake GW464: specific gravity and weight per gallon
- Paraffin wax (Wikipedia): density and melting range
- Flints safety data sheet ROP206, white beeswax: relative density at 20 C
- NIST SP 811 appendix B: US fluid ounce, ounce and pound conversion factors
- Craftybase candle fragrance load calculator: container size times wax gravity gives the fill weight