Protein Concentration Calculator
Determine protein concentration from absorbance using the Beer-Lambert law.
About Protein Concentration Calculator
The Beer-Lambert law is linear only between roughly 0.05 and 1.5 absorbance units. Outside that window, stray light and detector saturation make readings unreliable regardless of the arithmetic. Absorbance at 280 nm depends on tryptophan and tyrosine content, so the extinction coefficient is protein-specific and must not be assumed.
Formula
Protein Concentration
A = ε c l, so c = A ÷ (ε l), then × dilution factor
- ε
- Molar extinction coefficient at 280 nm
- l
- Cuvette path length in centimetres
Worked example
With the default values below, Protein Concentration Calculator returns Concentration of 0.98633. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Absorbance at 280 nmminimum 0
- 0.65
- Molar extinction coefficientminimum 1 M-1 cm-1
- 43,824 M-1 cm-1
- Path lengthminimum 0.01 cm
- 1 cm
- Protein molecular weightminimum 1 Da
- 66,500 Da
- Dilution factorminimum 1 x
- 1 x
Results
- Concentration
- 0.98633 mg/mL
- Molar Concentration
- 0.000014832 mol/L
- Concentration
- 14.8321 uM
- Protein Mass in One Millilitre
- 0.98633 mg
- Verdict
- Absorbance within the reliable linear range
Step by step
- 1Values used
- 2Protein Concentration
- 3Concentration= 0.98633 mg/mL
- 4Molar Concentration= 0.000014832 mol/L
- 5Concentration= 14.8321 uM
- 6Protein Mass in One Millilitre= 0.98633 mg
- 7Verdict= Absorbance within the reliable linear range
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 9 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 Protein Concentration calculated?
A = ε c l, so c = A ÷ (ε l), then × dilution factor The Beer-Lambert law is linear only between roughly 0.05 and 1.5 absorbance units. Outside that window, stray light and detector saturation make readings unreliable regardless of the arithmetic.
Why does Protein Concentration matter?
Absorbance at 280 nm depends on tryptophan and tyrosine content, so the extinction coefficient is protein-specific and must not be assumed.
What values do I need to enter?
This calculator takes 5 inputs: Absorbance at 280 nm, Molar extinction coefficient, Path length, Protein molecular weight, Dilution factor. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.