qPCR standard curve calculator (efficiency, R², unknowns)

How to use (3 steps)

Paste standard points (Quantity, Ct) or load a CSV file. Rows with the same Quantity are treated as replicates.
Choose a regression method (OLS/WLS) and options such as 95% bands. Enter unknown Ct values if you have them.
Click Calculate to see the standard curve, efficiency, QC checks, unknown estimates, and step log. Share URLs keep the same settings.

Recommended order

First, build a standard curve (this page)
Next, review PCR efficiency (%) → Jump to efficiency
If needed, calculate relative expression (ΔCt / ΔΔCt) → ΔCt / ΔΔCt

Go deeper

Linear regression & correlation
How to read residuals and 95% bands
Descriptive stats
Check replicate variability

Data input and options

Preset examples

Defaults are examples. Selecting a preset replaces standard/unknown data and settings. For your own data, paste and click Calculate (or Reset). Jump to results

Standard points (Quantity, Ct[, w] per line)

CSV/TSV file (standard points)

Decimal Delimiter

Unknown samples (Sample, Ct optional)

Unknown dilution factor DF (optional)

Regression method Weights (WLS) Intercept Data used for regression

WLS weighting tips

WLS fits with point-wise weights. 1/Q and 1/Q² increase the influence of low-quantity points. Use the w column to set weights per point.

95% confidence band 95% prediction band Dilution factor D (for QC) Custom D

Auto-calculate

Results (summary)

PCR efficiency (%)

Calculated from slope m as Efficiency = (10^(-1/m) - 1) × 100. The range shown is a guide.

Results will appear here.

Ranges are guides. For research/education, review standard points and residuals together.

Quality checks (guide)

Concentration levels (mean ± SD)

Quantity	log10Q	n	Ct_mean	Ct_SD

Standard points (fit rows)

Advanced columns in standard table

Advanced columns (weight / yhat / residual / leverage / cooksD) can be toggled.

Quantity	log10Q	Ct	weight	yhat	residual	leverage	cooksD

Unknown samples (Ct → Quantity)

Sample	Ct	log10Q_hat	Quantity_hat	DF	Quantity_corrected

Standard curve and residuals

Standard curve (Ct vs log10(Quantity))

Hover points to see details.

Residual vs predicted Ct

Hover points to see details.

Calculation steps (How it’s calculated)

Notes for educators

Switch OLS/WLS and intercept on/off to compare how slope, residuals, and QC guides change.
With replicates, the mean and SD per level help discuss variability, outliers, and weighting.

FAQ

What is a qPCR standard curve?

A curve that relates standard quantity (copy number or concentration) to Ct by fitting Ct vs log10(quantity). It helps check linearity (R²) and amplification efficiency.

How many standard points are required?

At least two points are required to fit a line. For linearity and outlier checks, 4–6 points are recommended.

How is PCR efficiency (%) calculated?

From slope m: Efficiency = (10^(-1/m) - 1) × 100. The displayed range is a guide.

What does a slope around -3.32 indicate?

For a 10× dilution series, a slope near -3.32 corresponds to an apparent efficiency of about 100% (ideal guide).

Can efficiency exceed 100%?

Because it is inferred from the slope, apparent values over 100% can occur due to dilution error or inhibition. Treat it as a guide and check residuals and standard points.

Does the share URL include data?

Only settings (methods and band options) are saved. Standard and unknown data are not included.

What unit should I use for Quantity?

Any unit is fine (copy number, ng, concentration). Quantity must be positive for log10.

References (notes)

Guides shown on this page are general references. For research/education, consult primary sources as needed.

Comments

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