What is a good qPCR efficiency?

Many qPCR workflows accept roughly 90-110% efficiency, but the correct threshold depends on assay design, sample type, and lab validation rules.

Why is the qPCR standard curve slope negative?

Ct values decrease as template concentration increases, so plotting Ct against log concentration normally produces a negative slope.

Can I use this for RT-qPCR?

Yes. The calculation is the same when you are validating RT-qPCR amplification efficiency from a standard curve.

Is PCR efficiency enough to validate an assay?

No. You should also inspect R², melt curves or probe specificity, primer dimers, controls, and replicate variation.

PCR Efficiency Calculator

Convert a qPCR standard curve slope into amplification efficiency, percent efficiency, and a quick assay-quality check.

Standard curve slope

PCR Efficiency Formula

E = (10^(−1/slope)) − 1

The qPCR efficiency calculator converts the slope of a log dilution standard curve into per-cycle amplification efficiency. A slope near -3.32 corresponds to about 100% efficiency, meaning the target approximately doubles during each cycle.

Symbol	Variable	Description
slope	Standard curve slope	The slope from Ct or Cq values plotted against log template concentration.
E	Amplification efficiency	The fractional increase per PCR cycle before converting to percent.

How to Use the qPCR Efficiency Calculator

1
Build a dilution series
Run a standard curve from serial dilutions of your template, ideally across the range used by your samples.
2
Enter the standard curve slope
Use the slope from the regression of Ct or Cq against log10 concentration. The value is usually negative.
3
Check the percent efficiency
Read the calculated PCR efficiency and compare it with your lab's assay-acceptance range.

What PCR Efficiency Means

PCR efficiency describes how much target DNA increases each cycle during the exponential phase of qPCR. A perfect reaction doubles target every cycle, which is reported as 100% efficiency. Lower efficiency can suggest inhibitors, poor primer design, degraded template, or suboptimal reaction conditions.

Efficiency result	Interpretation
100%	Twofold amplification per cycle
90-110%	Common practical acceptance range
>110%	Review for primer dimers, nonspecific amplification, pipetting error, or a weak standard curve

Common Slope Benchmarks

The slope gives a fast quality signal before you interpret relative expression or copy-number results. A slope near -3.32 is ideal for a twofold amplification model.

Standard curve slope	Approximate efficiency	Signal
-3.58	90%	Often acceptable
-3.32	100%	Ideal twofold model
-3.10	>110%	Review carefully

Also check R², melt curve specificity, no-template controls, and replicate consistency.

PCR Efficiency FAQ

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