Ideally the efficiency of a PCR should be 100% and qPCR tutorials online say that it should be somewhere between 90% to 100 %. In one of the recent talks that I attended, I was told that if my PCR has an efficiency of over 90% I should have a relook at my results because it is generally rare to get such high efficiency. I know it depends on a lot of factors ranging from primers, reaction conditions, chemistry to cycles as well. On a general note, what is the average efficiency of a PCR in practice?