Angular conversion between 2*theta and q in small-angle scattering (SAS)

Select either conversion from 'q (or d) to 2*theta' or '2*theta to q (or d)', the range of conversion and the wavelength.
The angular units of 2*theta are in degree (0 -180) and q has the same (but reciprocal) unit as the wavelength, d has the same unit as the wavelength .
So if the wavelength is given in nm, q will be in inverse nm (or d will be also in nm). q is in reciprocal units, d in real-space units (d = 2*PI /q).