Candle Math Equations
The hardest part of making candles is accurately measuring the amount of wax and fragrance oil you need for your containers.
In this guide, we’ll walk through three fundamental equations for making candles so you can be sure what you’re not wasting a drop on your next batch of candles.
By the end of this post you should understand the theory of candle math.
Equation 1: Total Weight
Total Weight = Water Weight x Specific Gravity x Total Candles
Equation 2: Wax Weight
Wax Weight = Total Weight ÷ (1 + Fragrance Load)
Equation 3: Fragrance Oil Weight
Fragrance Oil Weight = Wax Weight x Fragrance Load
or
Fragrance Oil Weight = Total Weight – Wax Weight
Full instructions and explanation below.
Basic Theory
Building A Sweet Scent
Almost every candle has wax and fragrance oil.
These equations hold true whether you’re using a normal wax, like soy, a premium blend, like coco créme beeswax, or a custom blend of whatever you want.
Before you do anything you need to figure out one thing: fragrance load.
Fragrance takes up a significant amount of space in the candle, anywhere from 3% to 12% by weight.
How do you decide on a fragrance load?
Every wax has a total allowable fragrance (max fragrance) it can hold. This amount is typically listed by the supplier or the manufacturer, and depends on the wax in question.
Wax can only hold so much extra “stuff”, including fragrance oil and additives, and your design must respect that amount otherwise it could leak out and become a fire hazard.
Think of the wax like a sponge: it can only absorb so much before reaching capacity.
Turning Water Into Wax
Wax weighs less than water.
Meaning, if you placed a block of wax next to an equally sized block of water, they would be the same size but not the same weight.
As a general rule of thumb, you can convert water weight into wax weight by multiplying by 0.86 because wax is approximately 86% as dense as water.
Some wax is less dense, and some is more – read more about that here.
Applying this idea to candle making, we can figure out how much total weight our candle is to find out how much wax and fragrance oil we need.
One more note: never measure out supplies in fluid ounces (fl oz).
Fluid ounces measure volume, but we want to measure weight. Instead use:
- ounces (oz)
- grams (g)
…and all the equations below work for both as long as you stick with one unit throughout!
Before You Start
- Determine a fragrance load. If you need a suggestion, use 6% if you’re not using palm wax. Otherwise use 3% if you’re using palm wax. If you are planning on combining multiple fragrances, that doesn’t affect this step.
- Assume a specific gravity/density of 0.86. This is a global average if you have nothing else to go off of. Learn about measuring the specific gravity/density of your specific wax here.
Remember: these equations are merely an estimate!
Candle math is meant to put you in the right ballpark with your supplies and equipment, not to micro manage your work.
Ideally you can optimize how supplies are consumed, limit waste, and maintain quality control with excellent notes.
Equation 1: Total Weight
Total Weight = Water Weight x Specific Gravity x Total Candles
Before we can break down the measurements into wax and fragrance, we have to know how much the entire candle weighs.
The Total Weight is the wax AND the fragrance oil, not just the wax.
Everything in candle making is measured by weight – click here to learn four reasons why.
You’ll convert water weight into wax weight in this step, which means you have to know the specific gravity (also referred to as relative density). If you don’t have anything else to go on, use a value of 0.86 for the specific gravity.
Check out this resource if you want to find the actual specific gravity for your wax.
Put it all together and you should have the total weight of ONE candle.
Multiply that number by the total candles you will make from this batch to find the actual total weight.
Summary
- Measure the weight of the empty container/mold
- Fill container or mold with water and measure the weight
- Subtract the empty weight (#1) from the water weight (#2). This is the water weight for one candle.
- Multiply value in step 3 by 0.86 (or your calculated value for Specific Gravity)
- Multiply value in step 4 by the total number of candles in your batch.
Equation 2: Wax Weight
Wax Weight = Total Weight ÷ (1 + Fragrance Load)
Wax weight is the total weight of wax included in your candle. Seems pretty obvious, but a lot of people confuse this with Total Weight.
The only time Wax Weight is the same as Total Weight is when you aren’t using fragrance oil (fragrance load of 0%).
Every other time, follow these steps to determine your wax weight.
The variables:
- f = fragrance load, expressed as a decimal (7.5% would mean f = 0.075)
- TW = total weight, expressed in grams or ounces (found in Equation 1).
- Wax Weight = weight of wax in batch, expressed in grams or ounces
Summary
- Transform your desired fragrance load into a decimal. We’ll call this f.
- Add 1 to f. Example: 1 + 0.075 = 1.075
- Divide Total Weight by value from Step 2. This is Wax Weight.
For example, if you had:
- fragrance load = 7.5%
- TW = 186 grams
Following the steps:
- f = 7.5% ÷ 100 = 0.075
- 1 + 0.075 = 1.075
- Wax Weight = 186 grams ÷ 1.075 = 173 grams
Custom Wax Blends
If you have custom wax blends or intend on combining multiple waxes together for this batch, follow the extended steps here:
- Determine the split between all the waxes in terms of percentage.
- Multiply each wax percentage by the Wax Weight found earlier.
For example, if you intend on blending 90% paraffin with 10% coconut:
- Paraffin = 90% x 173 grams = 156 grams paraffin
- Coconut = 10% x 173 grams = 17 grams
If you wanted to blend four different waxes, the logic still applies:
- Paraffin 1 = 40% x 173 grams = 69 grams
- Paraffin 2 = 20% x 173 grams = 35 grams
- Soy 1 = 25% x 173 grams = 43 grams
- Soy 2 = 15% x 173 grams = 26 grams
Be careful when you round your results so you don’t lose numbers. Round up or down to complete the math if you need to.
You should still end up with a Total Wax equal to what you found in the initial calculation before splitting it across each wax type.
Equation 3: Fragrance Oil Weight
Fragrance Oil Weight = Wax Weight x Fragrance Load
or
Fragrance Oil Weight = Total Weight – Wax Weight
Finding your required fragrance oil is often the easiest calculation!
All you need to accomplish this is the wax weight and the fragrance load you used to find it.
Summary
- Multiply Wax Weight by Fragrance Load (expressed as a decimal)
Note: if your blend combines multiple waxes, use the total weight of all the waxes for this calculation and ignore the individual splits.
For example, if you have:
- Fragrance load = 7.5% (0.075)
- Wax Weight = 173 grams
Following the steps:
- Fragrance Oil Weight = 173 grams x 0.075 = 13 grams.
Alternatively, you could subtract the Wax Weight from the Total Weight (because theoretically all that remains is Fragrance Oil weight). Remember:
Total Weight = Wax Weight + Fragrance Oil Weight
which means we can rearrange it to say:
Fragrance Oil Weight = Total Weight – Wax Weight
Both are valid!
Custom Fragrance Blends
If you have custom fragrance blends or intend on combining multiple fragrance oils together for this batch, follow the extended steps here:
- Determine the split between all the fragrance oils in terms of percentage.
- Multiply each fragrance oil percentage by the Fragrance Oil Weight found earlier.
For example, if you intend on blending 40% lavender with 60% apples:
- Lavender = 40% x 13 grams = 5 grams
- Apples = 60% x 13 grams = 8 grams
13 grams in our example is a small amount to split because your final percentages will be off due to the small weight. You’ll end up with better results in larger batches.
Be careful when you round your results so you don’t lose numbers. Round up or down to complete the math if you need to.
You should still end up with a Total Fragrance Oil Weight equal to what you found in the initial calculation before splitting it across each fragrance type.
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