How is Forster distance calculated?

The Förster distance represents the molecular separation at which energy transfer is 50-percent efficient. Forster distance (R₀)for each donor-acceptor pair is calculated using the formula:

R?= 0.2108 [κ² Φ?n^-4J]^1/6 nm.  

‘κ’ is the orientation factor between two molecules, ‘Φ?’ is the quantum yield of donor fluorescence (without acceptor), ‘n’ is the refraction index of the medium surrounding the FRET pair, and ‘J’ is the overlap integral.

Forster distance is presented in nanometers for each FRET pair.