Classic candles, I was wondering the same just earlier today. I was doing a test burn on a couple 1/2 pints, and I was wondering, why 3 hours? I have always heard, burn in 3 hour intervals, why not 4, or 2? I guess everyone is different, and ks ranch explained it well! As far as getting the length of time that the entire candle will burn, I still haven't been able to do that one. Sometimes I'll get 12- 3 hour burns, sometimes its 15. Who knows!