It has recently been reported that X-ray emission from the hotspots of Cygnus A has been detected. Inverse Compton scattering of radio photons in the hotspots by relativistic electrons is able to account for the observed X-ray intensity. On the basis of the beam model of strong double radio sources, and taking into account the results of X-ray observations, we give the expressions for physical quantities of hotspots in terms of only the observed quantities. We applied the results to the hotspots of Cygnus A. The beam model gives consistent values for hotspot A. For hotspot D, however, it remains a difficulty on the beam velocity.