How to Calculate a Candle’s Burn Time

Why you measure instead of guess

Two candles with the same weight of wax can burn for very different lengths of time. The wick is a big reason. Suppliers point out that an over-wicked candle burns faster and an under-wicked candle burns slower. Wax type, fragrance, dye and jar all play a part too. So burn time belongs to your finished candle, not to the amount of wax in the jar.

The National Candle Association’s science activities describe the same basic idea: weigh the candle before and after burning for a set time, and you learn how much wax it used per hour. Published research on candle emissions also calculated burn rate this way, as mass used per hour.

How to measure burn rate, step by step

Before you start, make sure the candle already passes a basic burn test with no tunneling and no heavy soot. Timing a candle with the wrong wick only gives you a number for a candle you will not sell.

1. Weigh the finished candle. Subtract the empty container’s weight to get the net weight of the candle. Use grams if you can; they are easier to subtract. Use the same unit all through.
2. Trim the wick to about ¼ inch (6 mm), set the candle on a level, heat-resistant surface away from drafts, and light it. Write down the start time.
3. Burn for about four hours. Suppliers suggest roughly three to four hours for a first test. Longer tests give steadier data when you can do them, but guidance for jar candles says to put them out after four hours at a stretch.
4. Put it out and let it cool completely. Do not weigh it warm; liquid wax moves and the weight changes.
5. Weigh it again and subtract the container weight again.
6. Work out the rate. Weight before minus weight after is the wax used. Divide by the hours burned. That is your hourly burn rate.
7. Estimate total burn time. Divide the candle’s starting net weight by the hourly rate.

Why one test is not enough

The first burn can be a little off. A candle’s rate may also change as the wax level drops, because the jar holds more heat later in the burn. That is why guidance for burn testing says to judge a candle across its whole life, not only the first cycles.

• Repeat the test a few times and compare. Test several samples if you can; the NCA’s experiment guide suggests at least three samples for good data.
• Keep conditions the same. Room temperature, drafts, wick length and the candle itself should match from burn to burn.
• Measure again later in the jar. Do a timed burn near the middle and near the end. If the rate rises, your simple 50-hour estimate was too generous.
• Stop at a safe point. A common practice is to finish testing when only about ¼ inch of wax remains, so measure usable wax, not every last gram.

Record each session in a testing log: date, start and stop times, weights, wick, room and notes on the flame and pool.

An estimate is not a label claim

Any number from this method is an estimate for one formula and one set of conditions. If you want to print or advertise burn hours, keep the records behind it: wax, jar, wick, fragrance, dye, cure time, test conditions, every weight and the lit time. Re-test when anything in the formula changes, since a new wick or oil can change the rate.

Safety labeling is a separate topic. The industry’s ASTM F2058 standard covers the fire-safety warnings every candle should carry. It does not tell you how to figure out your burn time. For label rules see candle label requirements, and ask your state about its rules.

The CandleEasy Burn Time Calculator is a planning tool. Use your own measured numbers for any claim about a finished product.

Common mistakes

• Forgetting to subtract the container’s weight, which makes the burn time too long.
• Weighing a warm candle.
• Timing one burn and printing the answer.
• Burning a candle that tunnels or soots and treating its rate as typical.
• Mixing ounces and grams.