Fit your standard curve online, then calculate unknown sample concentrations instantly. Supports 4PL, linear, and log-linear regression.
How to Use This Tool
1
Enter Standards
Input known concentrations and their corresponding OD / RLU / signal values. Duplicates: enter each replicate on a separate row.
2
Choose Model
4PL is recommended for most ELISA. Use Linear or Log-Linear for simple assays with narrow dynamic range.
3
Fit Curve
Click Fit Curve. View the chart, R² value, and fitted parameters. A good fit has R² > 0.99.
4
Calculate Unknowns
Enter your sample signal values (one per line) and click Calculate to get concentrations.
Standard Curve Data
Step 1
Paste from Excel / spreadsheet: select two columns (Concentration + Signal), copy, then click in the box below and paste (Ctrl+V). Tab-separated, comma-separated, and space-separated all supported.
Concentration
Signal (OD / RLU)
rows parsed — preview:
Concentration
Signal
Tip: Include duplicate/triplicate rows with the same concentration — the tool will average them automatically.
Fitting Options
Step 2
Fitting Model
4PL recommended for most ELISA
Concentration Unit
Label only, does not affect calculation
Signal Label
e.g. OD 450nm, RLU, FU
Fitted Curve
Step 3
Enter standard data and click Fit Curve to see results here.
Goodness of Fit (R²)—
4PL Parameters
A (min)
—
B (slope)
—
C (EC50)
—
D (max)
—
Calculate Unknown Concentrations
Step 4
Please fit a curve first (Step 3).
Results will appear here.
About the Models
4PL — 4-Parameter Logistic
y = D + (A−D) / [1 + (x/C)^B] Best for sigmoid-shaped curves. Recommended for competitive and sandwich ELISA with wide dynamic range.
Linear Regression
y = mx + b Use only when the signal–concentration relationship is truly linear over the working range. Limited dynamic range.
Log-Linear (Semi-Log)
y = m·log(x) + b Linearizes the relationship for assays where signal is proportional to log(concentration). Does not handle zero concentrations.