Example (preset)
Choose an example to fill inputs and see results immediately.
- Paste standards (concentration and absorbance) or import a CSV/TSV file.
- Select assay (BCA/Bradford) and fit (auto/linear/quadratic).
- The standard curve and unknown concentrations appear (dilution factors supported).
Out-of-range estimates (extrapolation) can be inaccurate. Check warnings in the results. This is a calculation tool and does not prescribe experimental optimization.
Need help choosing blank handling or fit type?
Use this calculator for the actual BCA or Bradford fit, unknown concentrations, and exportable tables. Open the assay standard curves guide when you need the reasoning around blank subtraction, linear vs quadratic choice, range interpretation, and what belongs in the report.
Input (paste / CSV)
Weighting (optional)
Standards
Format: col 1 = concentration, col 2+ = absorbance (rep1, rep2, …). TSV/CSV supported.
Unknowns
Format: col 1 = sample name, col 2+ = absorbance (rep columns supported), optional last column: dilution_factor.
Advanced (point exclusion / residuals / CI)
Results
Plots
Table (standards)
| Concentration | Mean | SD | ŷ | Residual | Excluded |
|---|
Table (unknowns)
| Sample | Mean Abs | Conc (measured) | Dilution factor | Conc (stock) | In range |
|---|
Note: Out-of-range estimates (extrapolation) can be inaccurate.
Workflow
- Enter standards (concentration x and absorbance y). With replicates, the tool computes mean±SD.
- Optionally subtract blank (0 concentration) mean absorbance (applied consistently to standards and unknowns).
- Fit with linear (y=a+bx) or quadratic (y=a+bx+cx²) and show metrics (R²/RMSE/AICc).
- For unknowns, back-calculate concentration from absorbance and apply dilution factors to get stock concentrations.
FAQ
What is the difference between BCA and Bradford assays?
Both estimate protein concentration from absorbance. Curve shape can change by conditions and range, so this tool supports linear and quadratic fits.
What should I enter first?
Enter standards (known concentrations) and their absorbance. If you provide replicate columns, the tool computes mean±SD automatically.
Do I need blank subtraction?
Often, subtracting the 0-concentration (blank) absorbance improves stability. Apply the same blank subtraction to both standards and unknowns.
Should I use a linear or quadratic fit?
Quadratic may fit better over a wide range, while a narrowed range can be fine with a linear fit. Use auto comparison (AICc); if the difference is small, preferring the simpler linear model is often safer.
My unknown concentration is outside the standard range.
Out-of-range estimates are extrapolations and can be inaccurate. Consider adjusting dilution factors or the standard range.
How do I enter dilution factors?
You can enter a dilution factor per unknown row. Stock concentration is calculated as measured concentration × dilution factor.
Can I use these results in a paper or report?
Yes, but include key settings such as fit type (linear/quadratic), whether blank subtraction was used, and whether extrapolations were present, so the analysis is reproducible.
Interpretation and next steps
Keep this page focused on the fit itself. Move to the guide when you need to justify blank subtraction, decide whether a quadratic fit is worth the added complexity, or write the method in a way another lab member can reproduce.
- Assay standard curves guideRead this next for blank handling, fit selection, extrapolation checks, and reporting choices across protein assays and ELISA.
- ELISA standard curve fitter (4PL/5PL)Switch here when the assay is sigmoidal and you need 4PL or 5PL fitting rather than a protein-assay standard curve.
- A260 concentration & purity calculatorCheck nucleic-acid concentration and purity before the assay workflow when sample quality is still uncertain.
- Linear regression calculatorUse a simpler regression page when you want to inspect slope, intercept, and residual behavior without the full assay workflow.