Burn rate is a term used to determine how well a particular combination of wax and wick is working. It can happen that by altering the wax mixture and using a different wick you can have a longer-burning candle that is therefore less costly.
To find the burn rate, first weigh the candle. Then, burn the candle for a specific length of time; put it out and weigh it again, with any drippings. Unburned wax was not consumed as fuel by the flame.
Burn rate is usually figured in grams. Here's an example: your candle weighs 340 grams. After burning 1 hour, it weighs 40 grams. Therefore, each minute it burned (burn time) consumed 5 grams of wax. Your burn rate is 5 grams per minute.