Once you've decided to start on your candle project, it soon becomes apparent that you will need to calculate how much wax and scent is required for your container. We'll start with the container itself so we can determine the fill line (the point to which it will be filled to), keeping in mind that if it has a lid that will go on it, we'll need to allow enough space at the top so the wick won't get crunched. Typically, with whatever type of container, it looks best if it is not filled to the top, but has at least about 3/8ths of an inch left open at the top.
Note that this process entails using water in your container to figure it out, so this needs to be done well in advance of actually pouring your candle to ensure the container is absolutely dry, as any amount of remaining moisture will cause problems with your candle.
The weight we are looking for is the weight of water that has been poured to the desired fill line. You can either weigh the container when empty, make a note of it and deduct it from the combined weight of the container and the water, or tare your scale so it only measures the water weight.
To figure out the weight of the wax required, there needs to be an adjustment made for the difference in density between the water and the wax. The amount I've read for this is between 82% to 90% ... so the water weight is multiplied by something in between. I'm going to go with 86%, which is another figure I've seen noted. So, if the total weight of the water is 6.5 ounces, which is what it is, for instance, in an 8-ounce jelly jar, then the amount of wax will be 5.59 ounces. This is the 6.5 (ounces of water) multiplied by .86 which is the percentage adjustment for the approx. difference in water weight to wax weight.
To figure out the fragrance oil, we first need an idea of the percentage of oil that will be used with the type of wax. A paraffin wax may easily hold 10%, but some soy waxes may hold less, and that amount is going to vary based on the type of soy wax. This is important because if you add more fragrance oil than the wax can safely handle, there is going to be excess oil that could over saturate the wax. Over time, especially in soy wax, the oil could partially sink through the wax toward the bottom of the candle, making the wax too fragrance oil heavy.
For this example, let's use 8% as our guideline. If we have 5.60 ounces of wax, then our fragrance oil is going to be 5.60 x .08 = .448 ounce of scent. If the wax can safely hold 9%, then this of course can be rounded up to a half ounce. Adding this to the wax amount is going to make the total wax and scent six ounces, which is just about right for this size container.
If your calculations result in a little too much scented and/or colored wax, there are lots of creative ways to put it to good use. I never throw any wax away, except for spent wax at the bottom of burnt candles. All other wax becomes part of my scrap wax bin and there are usually some chunk candles up the road just waiting for it!
