Protein Concentration Calculator
Calculate protein concentration either directly from a measured mass and solution volume, or from an A280 absorbance reading using an extinction coefficient specific to your protein. There is no single universal A280-to-concentration conversion, so the absorbance mode requires your own coefficient.
Last updated: September 26, 2026
Frequently asked questions
Which mode should I use?
Use mass and volume if you know the actual mass of protein dissolved in a known volume. Use the A280 mode only if you have a published or measured extinction coefficient for your specific protein - a generic assumption is not reliable.
Why can't I just enter A280 without an extinction coefficient?
Absorbance at 280 nm depends heavily on each protein's tryptophan, tyrosine, and cystine content, so there is no single conversion factor that works for every protein the way there is for nucleic acids. Using the wrong assumed coefficient can give a badly wrong concentration.
Where do I find my protein's extinction coefficient?
It is often published in the literature for known proteins, or can be calculated from the amino acid sequence using established methods, or measured directly. Check a reference specific to your protein rather than guessing.
How is this different from the DNA Concentration Calculator?
The DNA Concentration Calculator uses standard A260 conversion factors that are considered roughly universal for nucleic acid types. Protein absorbance conversion is protein-specific, which is why this tool requires your own coefficient instead of assuming one.
What does dilution factor do in the A280 mode?
If you diluted your sample before measuring absorbance, multiply the calculated concentration back up by the dilution factor to get the concentration of your original, undiluted sample.
Can I use this for crude extracts or mixtures?
A280 readings for mixtures reflect the combined absorbance of everything present, not just your protein of interest, so this mode is most reliable for purified or well-characterized protein solutions.