Without actually pouring wax into a container, how do you know how much wax it will hold? In short, this is how to do it (with details after the summary):

1. Find out how much water (weight in ounces) the jar will contain when filled to the desired wax fill line.
2. Find the specific gravity (or density) of your wax from the MSDS.
3. Multiply the water weight by the specific gravity to get the wax weight.

Step 1: Find the water weight

First thing we need to do is figure out how much water weight will fill the vessel to the fill line. You can weigh your vessel empty, and then weigh it filled; the difference will be water weight. OR, if you have a scale with a tare function, place your vessel on the scale, tare to zero, and then pour water in until it reaches the wax fill level you would like.

Step 2: Find the specific gravity of the wax

A reputable wax supplier will provide the MSDS for the waxes they sell. I use Ecosoya Q210 and I purchased my wax from Candlescience. On Candlescience’s website, I download the MSDS for my wax here.

In the MSDS, I look for mention of specific gravity or density… and yup, as I expected, here it is:

So now I know my specific gravity! I choose 0.89, the smaller number, because it’s always better to have too much wax than too little.

Step 3: Math!

In step 1, I found that my water weight is 12.85 oz. In step 2, I found that my specific gravity is 0.89. The math is super easy:

12.85 oz x 0.89 = 11.43 oz

I round that up to 11.5oz, and voilà: My wax (and FO) fill weight for the Shadowfire single wick vessel is 11.5 oz!

One question I occasionally get is, “How do I estimate how long my candle will last?” Here’s how!

Important Note

It is important to note that wax consumption will depend on the fragrance oil that is mixed in with the wax and also the wick’s capacity and number of wicks. This means that if you change fragrance, fragrance percentage, wax, or wick, you will need to re-test and recalculate your burn rate again. It’s easiest to do this during wick testing.

Step One: Gathering Data

During the wick testing phase, you’ll be testing for the ideal melt pool, hot throw, and vessel sturdiness. One more thing you can do while testing is record start and end candle weights.

1. Weigh the candle: wick, wax, vessel, fragrance oils, decorations, and all. If your candle vessel has a lid, exclude it, don’t weigh it.
2. When you start your test, record the starting weight and the time you light the candle.
3. At the end of your test, blow out the candle. Weigh the candle again and record the ending weight and ending time.

Step Two: Calculations (with Example!)

The starting weight less the ending weight will give you the weight of the wax consumed during the burn. For example, I recently tested a candle that started the test at 498g and ended at 487g.

498g – 487g = 11g

We also need to figure out how long the candle burned. For example, the candle was lit at 10:15am and it was blown out at 12:10pm.

12:10pm – 10:15am = 1 hour and 55 minutes burn time

Now, take the weight of the wax consumed during the burn and divide it by the number of hours burned. (You can use minutes if you like.) This will give you a wax burn rate.

11g / 115 minutes = 0.096g/minute

To convert this to hours:

0.096g/minute x 60 minutes = 5.76g/hour

Step Three: Find Your Candle’s Burn Time

When you finally pour your candles, you should know how much wax is in each one. For the candle in our example, I decided that they would be 12.5oz each (not including vessel or wicks, but including wax and FO.) Since my burn rate is in grams, I’ll convert ounces to grams (it’s more accurate that way). Google makes it easy. 12.5oz is 354g.

Now I divide the weight of the wax (and fragrance oil) by my burn rate.

354g / 5.76 g/hr = 61.45 hours

Woot! We figured out that a 12.5 oz candle will probably burn for just under 61.5 hours. Since candles may burn faster or slower depending on where they are located (for example near a draft or in a still room) I like to couch the burn estimate in range, so I would then put the estimated burn time as 55 – 65 hours.

Most candle supply stores sell pre-cut, primed, and tabbed wicks, and most of the time those will be all the wick you ever need. Sometimes, however, you need a really long wick for a tall container. Or you need a particular size but no one has it in stock or sells it.

You can buy spools of raw wicking (and tabs). I get mine from Candlewic (I don’t have any affiliation with them, but I use them as a supplier for my business too.)

Raw wicks on spools will look a little different from what you are used to when you buy pre-tabbed wicks. The wicks don’t stand up on their own because there is no wax to stiffen them. Likewise, because raw wick is literally braided and woven cotton threads, these will have air bubbles that will either be trapped in the wick or will create bubbles around your wick when you use them.

While I could work with raw wick directly, I prefer to pre-prime my wicks. For this, any type/color of wax will work! The only thing is to make sure the wax you use has a higher melting point. I use white beeswax because I make lip balm and I always have some beeswax lying around.

First I cut the wicks to the length I want. Right now I am still testing wicks, so I cut them pretty long (I’ll cut them into thirds after they’re primed). I then drop the wicks into the melted beeswax and stir them around until I’m sure they’re soaked through. Then I pull on some poly/plastic gloves to protect my hands.

I fish out the wicks with a skewer or with tweezers, and then lay them on parchment paper or wax paper. I have a very small window in which I won’t burn my fingers (from hot beeswax) and I quickly straighten and smooth out the wicks by pulling them between my fingers and laying them out on the wax paper.

If I work too slowly the beeswax solidifies on me and leaves me with a tangled mess, but if that happens I drop the clump back into the melted beeswax in my cup and it all melts down again. (I should have taken pictures during this process but was too busy to do so. Next time, I’ll do it and put up a TikTok video!)

It doesn’t take long for my straightened wicks to be ready for me to pack them up for future use. I bought tabs and I have pliers–I will use some of these in candles and tab them as I wick the vessels.

I am going to experiment with dying the beeswax in the future. Just imagine: red wicks in green wax for Christmas, purple wicks in pink wax for Valentine’s Day, or red-white-blue wicks in a triple wick candle for Independence Day. The possibilities are endless…