qPCR Efficiency Calculator
PCR amplification efficiency is calculated from the slope of a Ct vs log10(quantity) standard curve. A slope of -3.32 indicates 100% efficiency (perfect doubling). This calculator performs linear regression on your standard curve data (Ct vs log10 of quantity) to determine the slope, y-intercept, R-squared, and efficiency. Enter standard curve quantites (copies, ng, or any consistent unit) and their corresponding Ct values in matching order. Results comply with MIQE reporting requirements.
qPCR efficiency formula
Ct = slope * log10(quantity) + intercept
E (%) = (10^(-1 / slope) - 1) * 100
For a perfectly efficient reaction, each cycle doubles the template: E = 2.00 (100%). The slope of the Ct vs log10(quantity) regression line should be -3.32 for E = 100%. Acceptable range: -3.10 to -3.60 (corresponding to 90 to 110% efficiency). Source: Bustin et al. (2009), Clinical Chemistry, MIQE guidelines.
MIQE efficiency reporting requirements
- Report efficiency as a percentage (90 to 110% is acceptable).
- Report the R-squared of the standard curve (R2 above 0.99 is required).
- Report the slope and y-intercept of the standard curve.
- Use at least 5 standard points spanning at least 4 orders of magnitude.
- Run each standard in triplicate and use the mean Ct for curve fitting.
qPCR efficiency: frequently asked questions
What is qPCR efficiency?
PCR efficiency (E) describes how well a PCR reaction doubles the target DNA each cycle. An efficiency of 100% (E = 2.0) means the target perfectly doubles each cycle. Efficiency is calculated from the slope of a standard curve: E = 10^(-1/slope) - 1, where slope is from a plot of Ct vs log10(quantity).
What is an acceptable qPCR efficiency range?
Acceptable qPCR efficiency is 90 to 110%, corresponding to E values of 1.90 to 2.10. The MIQE (Minimum Information for Publication of Quantitative Real-Time PCR Experiments) guidelines specify that efficiency must be reported and should fall within this range for valid relative quantification.
How is qPCR efficiency calculated from the standard curve slope?
qPCR efficiency = (10^(-1/slope) - 1) * 100%. A perfect doubling efficiency gives a slope of -3.32 on a Ct vs log10(quantity) plot. Slopes between -3.1 and -3.6 correspond to efficiencies of 90 to 110%.
Why does efficiency affect relative quantification (delta-delta Ct)?
The delta-delta Ct method assumes 100% efficiency (E = 2). If reference and target genes have different efficiencies, the result will be inaccurate. If efficiencies differ by more than 10%, use efficiency-corrected relative quantification (Pfaffl method) instead.
What is the MIQE guideline and why does it matter?
MIQE (Minimum Information for Publication of Quantitative Real-Time PCR Experiments) is a set of guidelines published in Clinical Chemistry (Bustin et al., 2009) that define the minimum data required for qPCR experiments to be reproducible. Reporting efficiency, R-squared, primer sequences, and annealing conditions are required by MIQE-compliant journals.
Official sources
- Bustin S.A. et al. (2009). The MIQE Guidelines: Minimum Information for Publication of Quantitative Real-Time PCR Experiments: Clinical Chemistry, NCBI PubMed Central.
- NCBI NIH qPCR primer design guide: NCBI Primer-BLAST.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.