AAT Bioquest

Protein Concentration Calculator

The concentration of Protein in solution can be determined by substituting the molecular weight, extinction coefficient and λ max into a derived form of the Beer - Lambert Law. A substance's λmax is the wavelength at which it experiences the strongest absorbance. For Protein, 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 280 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 type. Or select "custom sequence" to enter the amino acid sequence or the UniProt ID.

  2. Enter the absorbance at λmaxFor 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.

Data Entry

Absorbance at λmax
Dilution factor (optional)
Pathlength cm


Have a question or a feature request about this tool? Feel free to reach out to us and let us know! We're always looking for ways to improve!

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This online tool may be cited as follows


"Quest Calculate™ Protein Concentration Calculator." AAT Bioquest, Inc.28 May2024https://www.aatbio.com/tools/calculate-protein-concentration.


AAT Bioquest, Inc. (2024May 28). Quest Calculate™ Protein Concentration Calculator. AAT Bioquest. https://www.aatbio.com/tools/calculate-protein-concentration.

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