qPCR Efficiency From Slope or Standard Curve
What is qPCR efficiency?
qPCR efficiency describes how well your target amplifies each cycle. In an ideal reaction, the amount of product doubles every cycle, which corresponds to about 100% efficiency.
How this calculator works
You can calculate efficiency from the slope of a standard curve, or compute the slope from dilution series data. The relationship is based on a linear fit between Ct and the log of starting quantity:
\( Ct = m\cdot \log_{10}(Q) + b \)
Once the slope \(m\) is known, efficiency is computed as:
\[ \text{Efficiency}(\%) = \left(10^{\left(\frac{-1}{m}\right)} - 1\right)\cdot 100 \]
Interpreting results
As a practical guideline, many labs aim for efficiency around 90% to 110%, with a slope near -3.32. When using dilution data, this calculator also reports \(R^2\) to summarize how well the points match a straight line.
Common issues that reduce efficiency
- Inhibitors carried over from extraction or sample matrix.
- Pipetting variation across dilution points.
- Primer design problems, including off-target binding or dimers.
- Template quality issues such as degradation or contamination.
Notes about the table
When using dilution points, the table includes predicted Ct values and residuals for each point. Large residuals may indicate an outlier or inconsistent dilution preparation.