A280 Protein Concentration Calculator

1Choose Method: BCA Assay • Bradford Assay • Direct A280
How to use: pick a method below (Step 1), then for BCA or Bradford build a BSA standard curve in Step 2 (Direct A280 instead asks for extinction coefficient, MW and path length). Enter your unknown samples in Step 3 and read the calculated concentrations in Step 4. Need the extinction coefficient for A280? Use the Protein MW & Extinction Coefficient Calculator.
2Standard Curve (BSA Standards)

Enter known concentrations and absorbance at 562 nm. Blank-subtract your readings first.

Conc (µg/mL)Abs (562 nm)
3Unknown Samples

Enter sample name, absorbance (blank-subtracted), and dilution factor.

NameAbs (562 nm)DilutionConc (µg/mL)
Standard Curve
4Results Summary
2Standard Curve (BSA Standards)

Enter known concentrations and absorbance at 595 nm. Blank-subtract your readings first.

Conc (µg/mL)Abs (595 nm)
3Unknown Samples

Enter sample name, absorbance (blank-subtracted), and dilution factor.

NameAbs (595 nm)DilutionConc (µg/mL)
Standard Curve
4Results Summary
Protein Presets

Select a protein to auto-fill MW and extinction coefficient, or enter custom values.

2Parameters
Molar Extinction Coefficient (ε)
M-1cm-1
Molecular Weight (MW)
Da
Path Length
cm
ε 0.1% (1 mg/mL)
AU
3Sample Readings

Enter A280 readings. Values >2.0 may be unreliable due to detector non-linearity.

NameA280DilutionConc (mg/mL)
Concentration Chart
4Results Summary
Purification Yield Tracker

Track protein recovery across purification steps. Enter concentration and volume at each stage.

StepConc (mg/mL)Volume (mL)Total (mg)Step Yield (%)Cumul. Yield (%)
Frequently Asked Questions
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About the A280, BCA and Bradford Protein Concentration Calculator

This A280 protein concentration calculator covers all three of the standard quantification methods used in protein purification and bioprocess development: direct UV absorbance at 280 nm (Beer-Lambert law), the BCA assay (bicinchoninic acid colourimetric), and the Bradford assay (Coomassie G-250 dye binding). Accurate protein concentration data is essential for calculating purification yields, sizing chromatography loads, formulating drug substance, and reporting specific activity. Whether you searched for "a280 protein concentration calculator", "protein concentration calculator a280", or "how to calculate protein concentration from BCA assay", the workflow above handles your case in a few clicks.

The BCA assay (bicinchoninic acid) is widely used in bioprocess development because of its broad compatibility with buffers and detergents commonly found in downstream processing. The Bradford assay offers faster results but is sensitive to detergent interference. Direct A280 measurement provides real-time concentration data without reagents and is the method used by in-line UV monitors during chromatography. This calculator supports all three methods with standard curve fitting, automatic sample concentration calculation, dilution correction, and a purification yield tracker to follow protein recovery across your entire downstream process.

For related tools, try the Protein MW & Extinction Coefficient Calculator to determine the extinction coefficient needed for A280 measurements, or the Chromatography Column Calculator for sizing and loading calculations that depend on accurate protein concentration data.

A280 vs Bradford vs BCA: which protein assay to use

Choose A280 for purified, reagent-free proteins when you know the extinction coefficient; Bradford for a fast (~10 min) colourimetric read on low microgram amounts with no detergents present; and BCA for the widest range (~20–2000 µg) and the best detergent compatibility, provided your buffer is free of reducing agents and chelators. A280 is the only reagentless option but overestimates concentration when nucleic acids are present. Bradford has high protein-to-protein variability and is blocked by detergents, whereas BCA is the most forgiving of surfactants but is interfered with by DTT, BME, EDTA and other reducing agents or metal chelators. The table below summarises how the three methods compare at a glance.

Method Principle Wavelength Linear range Time Detergent / reducing-agent compatibility Best use
A280 Intrinsic Trp/Tyr/cystine UV absorbance (no reagents) 280 nm ~0.1–3 mg/mL (protein-dependent) Seconds Reagent-free; sensitive to nucleic-acid contamination at 280 nm Relatively pure protein with a known extinction coefficient
Bradford Coomassie G-250 dye binding 595 nm ~1–20 µg ~10 min Incompatible with detergents; high protein-to-protein variability Fast reads on detergent-free samples
BCA Cu2+ reduction + bicinchoninic acid chelation 562 nm ~20–2000 µg 30 min at 37 °C Detergent-compatible, but interfered by reducing agents/chelators; lower protein-to-protein variability Wide range in detergent-containing lysates

Method references & further reading

Further reading