What is an acceptable qPCR efficiency?

An efficiency between 90% and 110% (E = 1.90 to 2.10) is generally accepted. Values close to 100% indicate that DNA doubles every cycle, which is ideal. Efficiencies below 90% suggest inhibitors, poor primer design, or suboptimal conditions; above 110% may indicate pipetting errors or primer dimers.

Why is the slope negative?

The standard curve plots Cq values (y-axis) against the log of template concentration (x-axis). As concentration increases, Cq decreases, so the slope is always negative. A slope of -3.32 corresponds to exactly 100% efficiency.

What does R² measure in a standard curve?

R² (coefficient of determination) measures how well the data points fit the linear regression line. An R² ≥ 0.99 is typically required for a reliable standard curve. Lower values suggest experimental variability or outliers.

What slope corresponds to 100% efficiency?

A slope of exactly -3.3219 (= -log₁₀(2) × 10, or equivalently -1/log₁₀(2)) corresponds to 100% efficiency, meaning each cycle perfectly doubles the template.

Can I use this for RT-qPCR?

Yes. The efficiency calculation is identical for both qPCR (DNA template) and RT-qPCR (RNA template). In RT-qPCR the standard curve is typically generated from serial dilutions of RNA or cDNA.

How do I calculate efficiency without a standard curve?

Without a standard curve, you can use the LinRegPCR method or the Pfaffl method which estimates efficiency from the amplification curves of individual samples. This calculator uses the standard curve slope method, which is the most common approach.

qPCR Efficiency Calculator

Name: qPCR Efficiency Calculator
Availability: InStock
Author: Nham Vu

Enter your standard curve slope (and optional R²) to calculate qPCR amplification efficiency and assess assay quality.

Standard Curve Parameters

Enter the slope from your qPCR standard curve regression.

Standard Curve Slope *

Must be a negative number (typically between -3.10 and -3.90).

R² Value (optional)

Coefficient of determination from the standard curve (0 to 1).

Dilution Factor

The dilution series used. 10-fold is standard for most qPCR assays.

Formula Reference

E = 10^{(-1 / slope)} − 1

Efficiency % = E × 100
Ideal slope: −3.32 → 100% efficiency
Acceptable range: −3.58 to −3.10 (90%–110%)
R² ≥ 0.99 required for reliable quantification

Summary

Enter your standard curve slope (and optional R²) to calculate qPCR amplification efficiency and assess assay quality.

How it works

Run a serial dilution of your template (e.g., 5-fold or 10-fold) and perform qPCR.
Plot Cq (cycle quantification) values versus the log of template concentration to obtain a standard curve.
Record the slope from your qPCR analysis software (typically a negative number around -3.32).
Enter the slope into the calculator. The tool applies E = 10^(-1/slope) - 1 to compute efficiency.
The result is expressed as a percentage. Values between 90% and 110% indicate an acceptable assay.
Enter the R² value of your standard curve to get a linearity quality assessment alongside efficiency.

Use cases

Validate a new qPCR assay before use in quantification experiments.
Compare efficiency across multiple primer pairs or probe sets.
Troubleshoot assays that are under-amplifying or over-amplifying.
Document assay performance metrics for publication or regulatory submissions.
Quickly re-evaluate efficiency when standard curve conditions change.
Screen primer pairs during assay design and optimization.
Verify that reference gene assays meet efficiency requirements for normalization.
Confirm lot-to-lot consistency of reagents and master mixes.

Frequently Asked Questions

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Last updated: 2026-05-28 · Reviewed by Nham Vu