Weigh or Measure Candle Ingredients? Use a Scale

Weigh your wax and your fragrance oil. Fragrance load is a share of weight, so the amount has to be a weight too. CandleScience's beginner supply list calls a scale its top tip and says to ignore the fluid-ounce marks on your cups. Lone Star lists a digital scale so you do not have to convert fluid ounces to weight. Wholesale Supplies Plus says the same thing about oil: weight, not fluid ounces.

Why does volume give the wrong amount?

A fluid ounce measures space. An ounce on a scale measures weight. They only come close for water, and water is not what is in your pitcher. The number that links them is specific gravity, which is density compared with water (water is 1).

• Golden Wax 464 soy wax: 0.9 on one safety data sheet, and 0.89 to 0.92 g/ml at 25 C on the maker's 2023 EU sheet.
• White Sage and Lavender fragrance oil (CandleScience safety data sheet): 0.922.
• Plumeria fragrance oil (same supplier): 0.91834.

Oils differ from each other, and from wax, and your own oil's number is on its safety data sheet. One US fluid ounce of water weighs about 1.043 oz (29.57 g), which is 29.5735 / 28.3495. Everything else is that number times its specific gravity.

Worked example: 8 percent of 16 oz of wax

You want an 8 percent load on 16 oz (454 g) of wax. The right amount is 16 x 0.08 = 1.28 oz (36 g) of oil by weight. Say you pour 1.28 fluid ounces from a cup instead. The second oil below is a made-up example.

• Oil at specific gravity 0.922: 1.28 x 1.043 x 0.922 = 1.231 oz. That is 1.231 / 16 = 7.69 percent, short by 0.049 oz (1.4 g).
• Denser oil, specific gravity 1.05 (example): 1.28 x 1.043 x 1.05 = 1.402 oz. That is 1.402 / 16 = 8.76 percent, over by 0.122 oz (3.5 g).

Neither miss ruins a candle. But if your wax tops out at 9 percent, the second oil is close to the edge, and you would never know. Switch oils and your "8 percent" quietly changes. Weighing removes the problem.

Wax works the same way. A pint (16 fluid ounces) of solid wax at specific gravity 0.9 weighs 16 x 1.043 x 0.9 = 15.0 oz, not 16. Flakes and pellets in a cup have air between them, so they weigh less than that. That is my observation, not a published number.

What kind of scale do I need?

Any digital kitchen scale or candle and soap scale works, per CandleScience. Put the pitcher on it, tare it to zero, then add the wax. For small jars I like a scale that reads to a tenth of a gram. 6 oz of wax at 8 percent takes about 14 g of oil, and a 1 g wobble is 1 / 14 = 7 percent of that dose. That is my own habit, not a standard.

Is there anything I can measure by volume?

Water, for finding how much a jar holds. You still weigh it: fill the jar with water to your fill line and weigh the water. Our guide on how much wax fills a jar shows the sums. Jar sizes printed on a label may be brim volume, so the scale is the honest reading.

Common mistakes

• Using the fluid-ounce marks on a glass measuring cup for oil.
• Switching to a new oil and assuming the old volume still gives the same load.
• Weighing the wax but pouring the oil by the capful.
• Forgetting to tare the pitcher, so the pitcher's weight counts as wax.
• Mixing grams and ounces in one recipe. One ounce is 28.35 g.

Questions

Is a fluid ounce the same as an ounce?

No. A fluid ounce is volume and an ounce is weight. For water they are close (1.043 oz per fluid ounce), but not for oil or wax.

Can I trust "1 oz of oil per pound of wax" when I measure in a cup?

The phrase means 1 oz by weight, which is 6.25 percent of the wax. Our guide on ounces per pound explains it. In a cup, 1 fluid ounce of a lighter oil is under 1 oz, and a denser one is over.

Does it matter for a single test candle?

The error in grams is small. The point is repeating it: if you cannot say what you poured, you cannot compare two test candles. Weigh from the very first one.