Standard Curve & 4PL Curve-Fitting Calculator
Fit the whole calibration range and read every unknown, with its residuals.
Try before you buy.
- Free preview: input labels and masked result rows; computed charts and complete exports stay locked.
- Locked until you unlock it: download and copy.
- Unlock: Pro pass, ₹179 for 30 days or ₹79 for 1 week, a one-time payment that never renews. Unlock: Pro pass, $5.99 for 30 days or $2.99 for 1 week, a one-time payment that never renews.
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Locked in the free preview. Batch runs unlock with a pass.
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About the Standard Curve & 4PL Curve-Fitting Calculator
Fit every standard you measured with a linear, log-linear, four- or five-parameter logistic or Michaelis–Menten model. Check the parameters, the residual of each standard and R², and read each unknown’s dilution-corrected concentration, or the reason it cannot be read. Whole plate-reader CSV files work, with no limit on their size.
The free preview shows the report’s rows with the computed values hidden; a Pro pass shows every value and chart, with copy and CSV, SVG or PDF downloads. A good fit does not show that an assay is valid, what its range of quantification is or that it suits clinical use: check the back-calculated standards and independent controls.
How to use it
- Paste or upload every standard and unknown well, and name the columns for type, ID, concentration (x), response (y) and the unknowns’ dilution.
- Choose a model that suits your response. Log-linear concentrations must be positive, and enzyme rates must not be negative.
- Select Calculate, and check every parameter, every residual and the calibration plot. Non-linear fits use your raw responses, unweighted, from several starting points.
- Check each unknown’s range and result; with a Pro pass, download the CSV, text, chart SVGs and a PDF report.
Examples
Standards (0, 2), (1, 5) and (2, 8); an unknown with a response of 6.5 at dilution 2
Intercept 2 and slope 3; the unknown reads 1.5 units, or 3 units after its dilution
Results keep the concentration and response units you use.
Method and sources
Linear: y = intercept + slope × x. Log-linear: y = intercept + slope × log10(x). 4PL: y = a + (d − a) ÷ (1 + (x ÷ c)^b); 5PL raises the denominator to a power g, with b, c and g positive. Michaelis–Menten: v = Vmax × x ÷ (Km + x). The Lineweaver–Burk plot shows the reciprocal data with the non-linear fit; it does not refit the reciprocals. See calibration-model considerations and NIST’s guide to non-linear regression.
Limitations
- Unweighted least squares is sensitive to outliers and may not suit assay data whose spread grows with the response; weighting and a validated calibration protocol are separate choices.
- A high R² or a converged fit is no evidence of analytical accuracy, and logistic parameters are unreliable when the standards do not reach the asymptotes.
- Unknowns outside the range of the standards are marked as extrapolated; a response beyond an asymptote gets an error instead of an invented concentration.
- The parameters: with b positive, d is the response at zero concentration and a the response at very large concentrations; in 5PL, c is a scale parameter, not necessarily the concentration at half response.
- Prediction intervals, detection limits, assay acceptance criteria and clinical interpretation are not estimated.
- PDF reports load their font from this site. A label the font cannot show gives a clear PDF error; the CSV, text and SVG files keep every label as you typed it.
Privacy
On this device: nothing is sent
Your data, the fits and the exports stay on this device. Only the report font loads from this site; nothing is uploaded and no AI is used.
Frequently asked questions
What do I get without a pass?
Without a pass, Standard Curve & 4PL Curve-Fitting Calculator shows input labels and masked result rows; computed charts and complete exports stay locked. Until you unlock it, the result can’t be downloaded or copied. A Pro, Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
Does this validate my experiment?
No. It calculates from the data you entered with the model it states. Check your sampling, the assay’s assumptions and independent controls.
Is there a limit on the number of wells?
No. Enter every well you measured; only your device’s memory limits a very large file.
What happens to a blank or invalid row?
It gets an error that names the row. A blank or an unquantified reading is never treated as zero or dropped silently.