When using the Debye-Scherrer equation for calculating particle size (D=Kλ/(β cos θ) does one have to halve the FWHM(β)? Must all angles be in Radians?

The Debye-Scherrer method is used to obtain X-ray diffraction measurements in powders.This method is applicable to crystallites ranging from 1.0 to 0.01 μm in diameter, but the grains must have good crystallinity.