qPCR Efficiency Calculator
Calculate qPCR amplification efficiency from a standard curve. Enter the slope (m) and this calculator finds: E = 10(−1/m) − 1 and %Efficiency = 100×E. Includes quick picks, steps, and a mini quality gauge.
Background
In qPCR, efficiency tells you how close your reaction is to doubling each cycle. A perfect reaction has 100% efficiency, which corresponds to a standard curve slope near −3.32 (for a 10× dilution series).
How to use this calculator
- Pick From slope (most common) or Two-point estimate.
- Enter the slope (or enter two Ct values + a dilution factor).
- Click Calculate to see efficiency (%) plus interpretation.
How this calculator works
- From slope: E = 10(−1/m) − 1
- Percent efficiency: %Eff = 100×E
- Two-point estimate: E = (dilution)(1/ΔCt) − 1
Formula & Equations Used
Efficiency (from slope): E = 10(−1/m) − 1
Percent efficiency: %Eff = 100×E
Two-point estimate: E = (dilution)(1/ΔCt) − 1
Example Problem & Step-by-Step Solution
Example 1 — Efficiency from slope
A standard curve has slope m = −3.32. Find efficiency.
- E = 10(−1/−3.32) − 1
- E ≈ 1.00
- %Eff ≈ 100%
Example 2 — Efficiency from slope (slightly low)
A standard curve has slope m = −3.80. Find efficiency.
- E = 10(−1/m) − 1
- E = 10(−1/−3.80) − 1 = 10(0.2632) − 1
- E ≈ 1.833 − 1 = 0.833
- %Eff = 100×E ≈ 83.3%
- Interpretation: efficiency is on the low side; check inhibitors, primer design, and pipetting accuracy.
Example 3 — Two-point estimate (Ct + dilution)
A 10× dilution shifts Ct from 18.2 (higher concentration) to 21.5 (lower concentration). Estimate efficiency.
- ΔCt = Ctlow − Cthigh = 21.5 − 18.2 = 3.3
- E = (dilution)(1/ΔCt) − 1
- E = 10(1/3.3) − 1
- E ≈ 2.009 − 1 = 1.009
- %Eff = 100×E ≈ 100.9%
- Note: a full standard curve (multiple points) is more reliable than a 2-point estimate.
Frequently Asked Questions
Q: What efficiency range is “acceptable”?
Many protocols use ~90–110% as a rule of thumb, but your assay may have different validation criteria.
Q: What does >110% efficiency usually mean?
Often a sign of non-specific amplification, primer-dimers, or dilution/standard-curve issues.
Q: Why is the ideal slope about −3.32?
Because a perfect doubling corresponds to a 10× dilution shifting Ct by ~3.32 cycles.
Q: Can I calculate efficiency from Ct values instead of a slope?
Yes—if you have two dilutions (and you know the dilution factor), you can estimate efficiency from ΔCt. But it’s less reliable than using the slope from a full standard curve.