What efficiency is acceptable?

Most guidelines accept 90–110% (slope −3.58 to −3.10) with R² > 0.98. Over 110% often means inhibitors or non-specific product; under 90% suggests suboptimal primers or degraded template.

Why can efficiency exceed 100%?

Usually an artefact — inhibitors carried through the dilution series, primer-dimers, or pipetting error making the slope too steep — not more than one copy per copy per cycle.

qPCR efficiency calculator

Calculate qPCR amplification efficiency from a standard-curve slope (Cq vs log quantity). A slope of −3.32 is 100% efficiency — a perfect doubling each cycle.

How it works

Formula

amplification factor = 10^(−1 ÷ slope); efficiency = factor − 1 (as a percentage, ×100). A slope of −3.322 gives a factor of 2.0 (a perfect doubling) = 100% efficiency.

Worked example

Slope −3.322: 10^(−1 ÷ −3.322) = 10^0.301 = 2.00, so efficiency = 2.00 − 1 = 100%. A steeper slope of −3.10 gives 10^0.323 = 2.10 → 110% efficiency.

When to use it

After running a dilution-series standard curve, to validate a qPCR assay. Acceptable efficiency is typically 90–110% (slope −3.6 to −3.1); values outside that flag inhibition, pipetting error or poor primer design.

Sensible defaults

The default slope −3.32 is the textbook 100%-efficiency value. Enter the slope your qPCR software reports from the standard curve.

FAQ

What efficiency is acceptable?: Most guidelines accept 90–110% (slope −3.58 to −3.10) with R² > 0.98. Over 110% often means inhibitors or non-specific product; under 90% suggests suboptimal primers or degraded template.
Why can efficiency exceed 100%?: Usually an artefact — inhibitors carried through the dilution series, primer-dimers, or pipetting error making the slope too steep — not more than one copy per copy per cycle.