ELISA Standard Curve Calculator
Interpolate concentration from absorbance using a four-parameter logistic curve.
About ELISA Standard Curve Calculator
The four-parameter logistic curve is sigmoidal, so precision collapses near both asymptotes where a large concentration change produces almost no absorbance change. The reliable region is roughly the central 15 to 85 per cent of the response range. Readings outside the central region should be diluted and repeated rather than reported, because the interpolation error there can exceed the measurement itself.
Formula
ELISA Standard Curve
4PL: A = bottom + (top − bottom) ÷ (1 + (C ÷ C₅₀)^slope), solved for C
- 4PL
- Four-parameter logistic model, the standard for immunoassays
- Hill slope
- Steepness of the transition between asymptotes
Worked example
With the default values below, ELISA Standard Curve Calculator returns Interpolated Concentration of 208.2329. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Sample absorbanceminimum 0
- 0.85
- Bottom asymptoteminimum 0
- 0.05
- Top asymptoteminimum 0.01
- 2.4
- Inflection point concentrationminimum 0.001 pg/mL
- 120 pg/mL
- Hill slopeminimum 0.05
- 1.2
Results
- Interpolated Concentration
- 208.2329 pg/mL
- Position Within the Curve Range
- 34.043%
- Within the Reliable Range
- Yes
- Usable Absorbance Range
- 2.3500
- Dilution Advice
- Within the reliable central portion of the curve
Step by step
- 1Values used
- 2ELISA Standard Curve
- 3Interpolated Concentration= 208.2329 pg/mL
- 4Position Within the Curve Range= 34.043
- 5Within the Reliable Range= Yes
- 6Usable Absorbance Range= 2.3500
- 7Dilution Advice= Within the reliable central portion of the curve
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is ELISA Standard Curve calculated?
4PL: A = bottom + (top − bottom) ÷ (1 + (C ÷ C₅₀)^slope), solved for C The four-parameter logistic curve is sigmoidal, so precision collapses near both asymptotes where a large concentration change produces almost no absorbance change. The reliable region is roughly the central 15 to 85 per cent of the response range.
Why does ELISA Standard Curve matter?
Readings outside the central region should be diluted and repeated rather than reported, because the interpolation error there can exceed the measurement itself.
What values do I need to enter?
This calculator takes 5 inputs: Sample absorbance, Bottom asymptote, Top asymptote, Inflection point concentration, Hill slope. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.