How much wax do I need for a candle jar?
Candle jars are sold by volume (fluid ounces or millilitres of water they hold), but wax is bought and measured by weight. Wax is lighter than water, so a jar that holds 8 fl oz of water does not take 8 oz of wax. Mixing up the two is the most common reason a batch comes up a jar short.
Step 1: find the real capacity
Don't trust the number in the listing until you've checked one jar. Put the empty jar on a kitchen scale, zero it, and fill it with water to the brim. The weight in ounces is its capacity in fluid ounces (1 fl oz of water weighs about 1.04 oz, close enough for candles); in grams, it's the capacity in millilitres. Jars sold as "8 oz" often hold 9 or 10 fl oz to the brim.
Step 2: decide how full you'll pour
You never fill to the brim. Most makers leave about half an inch (1-1.5 cm) of headspace, which works out to roughly 85-90% of the brim capacity for a typical tumbler. The calculator uses 90% by default; change it to match your jars.
Step 3: multiply by the wax factor
Container waxes weigh roughly 86% as much as the same volume of water, which is why you see "multiply by 0.86" in many supplier guides. Some blends differ a little, so check the data sheet for yours.
Fill weight = capacity x fill level x wax factor
That fill weight is wax plus fragrance oil together. Split it using your fragrance load (see fragrance load explained).
Worked examples (soy, 90% fill, 8% fragrance load)
| Jar (to the brim) | Fill weight | Wax | Fragrance oil |
|---|---|---|---|
| 4 fl oz | 3.10 oz (88 g) | 2.87 oz | 0.23 oz |
| 8 fl oz | 6.19 oz (176 g) | 5.73 oz | 0.46 oz |
| 12 fl oz | 9.29 oz (263 g) | 8.60 oz | 0.69 oz |
Step 4: add a little extra
Some wax always stays in the pouring pitcher, and a jar can crack or a pour can go wrong. Adding 5-10% to the batch is cheap insurance; the calculator's overage box does this.
Common mistakes
- Using the listing's "oz" as weight. It's volume. Weigh one jar of water to be sure.
- Forgetting the fragrance is part of the fill. If you add fragrance on top of a full jar's worth of wax, you'll be over by the fragrance weight.
- Measuring fragrance by volume. Fragrance oils vary in density. Weigh everything on the same scale.
- Scaling by eye. Twelve candles at 8 oz is not "about six pounds of wax". It's 4.3 lb at 90% fill, before overage.
Ready to try it with your own jars? Use the wax and fragrance calculator.