Protein Concentration Calculator (A280)
By Santaji GadepatilinUpdated October 27, 2026
M⁻¹cm⁻¹
43,824 M⁻¹cm⁻¹Da
66,463 Dacm
µM
calculatedmg/mL
calculatedType in any field to change it. Press × on a value to calculate that field instead.
How to use this calculator
Enter the A280 reading, the protein’s extinction coefficient and molecular weight, and the path length. The concentration is given in µM and mg/mL.
Formula
c = A280 ÷ (ε × l)
Example — BSA
A280 = 0.8, ε = 43,824 M⁻¹cm⁻¹, 1 cm:
- c = 0.8 ÷ 43,824 = 18.25 µM
- × 66,463 g/mol = 1.213 mg/mL
Frequently asked questions
How do I calculate protein concentration from A280?
c (M) = A280 ÷ (ε × l). Multiply by the molecular weight to get g/L, which equals mg/mL.
Where do I get the extinction coefficient?
From the amino-acid sequence (tryptophan, tyrosine and cystine content) using a tool such as ExPASy ProtParam.
What is the default protein?
Bovine serum albumin (BSA), with ε ≈ 43,824 M⁻¹cm⁻¹ and MW ≈ 66,463 Da.