Protein Concentration Calculator

The concentration of proteins in solution can be determined by substituting the molecular weight, extinction coefficient and λmax into a derived form of the Beer-Lambert Law. A substance's λmax is the wavelength at which it experiences the strongest absorbance. For proteins, this wavelength is 280 nm.

The absorbance at λmax can be measured using a spectrophotometer. There are some important things to keep in mind when measuring protein absorbance:

  1. The protein should be well-dissolved in solution. Protein precipitation will cause inaccuracies in concentration calculations.

  2. The absorbance reading should not exceed the maximum detection limit of the instrumentation. This can be identified by a plateau in the absorbance spectrum. If the absorbance spectrum plateaus, dilute the sample and try again.

  3. This calculator assumes a 1 cm pathlength for instrumentation. Standard cuvettes for spectrophotometers are typically 1 cm. If a different pathlength is used, value should be corrected during data entry.

How to use this tool:

1. Select the protein. Or select "custom sequence" to enter the amino acid sequence or the UniProt ID.

2. Enter the absorbance at λmax. For a typical protein, λmax is 280 nm. However, this value may change based on the protein. Please use the maximum absorbance as indicated by the spectrophotometric reading (ie. highest peak).

3. If the absorbance is obtained with a diluted sample, enter the dilution factor in order to determine the concentration of the original sample.

4. If pathlength differs from 1 cm, enter corrected value into pathlength textbox.

5. Press calculate to display the concentration.

NameNot identified
MWWaiting for sequence
Extinction coefficientWaiting for sequence
Absorbance at λmax
Dilution factor (optional)
Pathlength cm