The burn time of a candle depends on its weight. It is easy to calculate how long a candle will burn with an easy-to-use formula.
According to Candle Cauldron, the burn time of a candle can be calculated by weighing the candle and burning it for a set amount of time. For instance, the site suggests weighing the candle, burning it for three hours, and then weighing it again. With that information, the burn time of the candle can be calculated.
For instance, if the calculation is started with a 16-ounce candle, it should be burned for three hours and then reweighed. If it is now 15.5 ounces, then in three hours it burned only .5 ounces. By splitting the .5 ounces into three hours, the calculation shows that .16 ounces burns away within an hour. So, the total weight, which was 16, divided by .16 per hour equals the total burn time. The calculation comes out to 100 hours, which should be the longest time the candle will burn.
There is also another trick that can be used. In a standard 2-ounce candle mold, the mold is rated as a 15-hour mold. So, divided by two, each ounce should burn for 7.5 hours.