The simplest and most commonly used method is the dilution or standard curve method. This method calculates PCR efficiency using the linear regression slope of a dilution series based on the following equation:
E = 10(-1/slope) -1
The ideal slope is -3.32, which correlates to an amplification efficiency of 100%, meaning exactly one copy per cycle. Slopes in the range of -3.60 to -3.10 are generally considered acceptable for Real-Time PCR. These slope values correlate to amplification efficiencies between 90% (1.9) and 110% (2.1). The correlation coefficient or R2 value should be at least 0.985 or higher.