Home / Science & engineering / Biology / Protein standard curve

← Biology

Biochemistry Standard curve

Protein standard curve calculator (BCA / Bradford)

Build a standard curve and estimate protein concentrations of unknown samples. Supports linear/quadratic regression (auto compare AICc), blank subtraction, replicates (mean±SD), residuals, and point exclusion.

All calculations run in your browser; data is not sent.

Other languages ja | en | zh-CN | es | pt-BR | id | fr | hi-IN | ar

Example (preset)

Choose an example to fill inputs and see results immediately.

Description
—
How to use (3 steps)
  1. Paste standards (concentration and absorbance) or import a CSV/TSV file.
  2. Select assay (BCA/Bradford) and fit (auto/linear/quadratic).
  3. 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.

Input (paste / CSV)

Assay
Blank subtraction (0 concentration)
Blank mean: —
Weighting (optional)
Note
If SD is available, you can weight by 1/SD² (replicates recommended).

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)
Point exclusion
Click standard points on the plot to exclude/restore (Undo available)
Excluded
—

Results

Selected model
—
Equation
—
R²
—
RMSE
—
AICc
—
Comparison (auto)
—

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

  1. Enter standards (concentration x and absorbance y). With replicates, the tool computes mean±SD.
  2. Optionally subtract blank (0 concentration) mean absorbance (applied consistently to standards and unknowns).
  3. Fit with linear (y=a+bx) or quadratic (y=a+bx+cx²) and show metrics (R²/RMSE/AICc).
  4. 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.

How to use this calculator effectively

This guide helps you use Protein standard curve calculator (BCA / Bradford) in a repeatable way: define a baseline, change one variable at a time, and interpret outputs with explicit assumptions before you share or act on results.

How it works

The page applies deterministic logic to your inputs and shows rounded output for readability. Treat it as a comparison workflow: run one baseline case, adjust a single parameter, and measure both absolute and percentage deltas. If a result seems off, verify units, time basis, and sign conventions before drawing conclusions. This approach keeps your analysis reproducible across teammates and sessions.

When to use

Use this page when you need a fast estimate, a classroom check, or a practical what-if comparison. It works best for planning and prioritization steps where you need direction and magnitude quickly before investing in deeper modeling, manual spreadsheets, or formal external review.

Common mistakes to avoid

Interpretation and worked example

Run a baseline scenario and keep that result visible. Next, modify one assumption to reflect your realistic alternative and compare direction plus size of change. If the direction matches your domain expectation and the size is plausible, your setup is usually coherent. If not, check hidden defaults, boundary conditions, and interpretation notes before deciding which scenario to adopt.

See also

FAQ

What should I do first on this page?

Start with the minimum required inputs or the first action shown near the primary button. Keep optional settings at defaults for a baseline run, then change one setting at a time so you can explain what caused each output change.

Why does this page differ from another tool?

Different pages often use different defaults, units, rounding rules, or assumptions. Align those settings before comparing outputs. If differences remain, compare each intermediate step rather than only the final number.

How reliable are the displayed values?

Values are computed in the browser and rounded for display. They are good for planning and educational checks, but for regulated or high-stakes decisions you should validate assumptions with official guidance or professional review.

Can I share and reproduce this result?

Yes. Use the share or URL controls when available. Keep a baseline case and one changed case so others can reproduce your reasoning and verify that the direction and scale of change are consistent.

Is my input uploaded somewhere?

Core calculations run locally in your browser. Some pages encode parameters in a shareable URL, but no automatic upload is performed unless you explicitly share that link.