qPCR efficiency calculator.
Find your assay efficiency from a standard curve. Enter the slope of the Cq versus log-quantity line and the calculator gives the amplification efficiency and the fold per cycle.
Standard curve
LiveEfficiency = (10 to the power of minus one over the slope, minus 1) times 100. A slope of -3.32 is 100% efficiency, perfect doubling.
Amplification efficiency
100.2%
per cycle
Acceptable efficiency is usually 90 to 110% (slope -3.6 to -3.1). Calculations run in your browser; nothing you enter is stored.
How it works
Slope to efficiency
In qPCR, you build a standard curve by plotting the quantification cycle (Cq) against the log of template amount across a dilution series. The slope of that line tells you the amplification efficiency: efficiency equals 10 to the power of minus one over the slope, minus 1, expressed as a percentage.
A perfect reaction doubles the product every cycle, which gives a slope of -3.322 and an efficiency of 100%. The calculator turns any measured slope into an efficiency and a fold-per-cycle value.
Reference
Slope to efficiency.
Common standard-curve slopes and the amplification efficiency they give.
| Slope | Efficiency |
|---|---|
| -3.10 | 110% |
| -3.32 | 100% |
| -3.58 | 90% |
| -3.92 | 80% |
| -4.10 | 75% |
The full guide
The complete guide to qPCR efficiency.
What efficiency means, how the slope sets it, and what counts as a good assay.
What is amplification efficiency?
Efficiency is the fraction of template that is copied each cycle. At 100% the product doubles every cycle, an amplification factor of 2. Lower efficiency means less than doubling, which stretches out the curve and can bias quantification if standards and samples differ.
It is a key quality metric for any qPCR assay and is reported from the standard curve.
How the slope sets it
Plotting Cq against log10 of template amount gives a straight line whose slope encodes the efficiency. A slope of -3.322 means each ten-fold dilution shifts Cq by 3.322 cycles, exactly what perfect doubling predicts. The formula is efficiency equals 10 to the minus one over slope, minus 1.
Steeper slopes (more negative) mean lower efficiency; shallower slopes mean higher.
What is a good efficiency?
Most guidelines accept 90 to 110% efficiency, which corresponds to slopes between about -3.6 and -3.1. Outside that range suggests problems: inhibitors, poor primers, pipetting error or a bad dilution series.
An R-squared above 0.98 on the standard curve is also expected, showing the points fall on a clean line.
Fixing poor efficiency
If efficiency is off, check for PCR inhibitors, redesign primers, optimise the annealing temperature, and make the dilution series carefully with fresh dilutions. Efficiencies above 110% often point to pipetting error or primer-dimers rather than a real result.
Re-run the standard curve after changes and recompute the efficiency here.
The formula
Doubling,
measured.
Efficiency is 10 to the minus one over slope, minus 1. A -3.32 slope is a perfect 100%.
DNA copy number ›# qPCR efficiency
E = (10^(−1/slope) − 1) × 100
# worked example
slope −3.32 → 10^0.3012 − 1 = 100%Questions
qPCR questions.
How do I calculate qPCR efficiency?
+
From the standard curve slope: efficiency equals 10 to the power of minus one over the slope, minus 1, times 100. A slope of -3.32 gives 100% efficiency.
What slope means 100% efficiency?
+
A slope of -3.322. It means each ten-fold dilution shifts the Cq by 3.322 cycles, which is exactly what doubling every cycle predicts.
What efficiency is acceptable?
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Generally 90 to 110%, corresponding to slopes of about -3.6 to -3.1, with an R-squared above 0.98 on the standard curve.
Why is my efficiency over 100%?
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Usually pipetting error, primer-dimers or inhibitors rather than a real result. Remake the dilution series carefully and recheck primer design.
Is this qPCR efficiency calculator free?
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Yes. It is completely free with no sign-up, and every calculation runs locally in your browser, so nothing you enter is stored or sent anywhere.
About the developer
Jean Borg
Jean builds and maintains every calculator on freecalculators.pro from Malta, with a focus on tools that are fast, free and show their working. The qPCR efficiency calculator uses the standard slope formula and is for lab analysis.