High resolution x-ray diffraction (HRXRD) is used to accurately determine the AlAs mole fraction in AlxGa1-xAs samples over the complete alloy range. The AlAs mole fraction error in the HRXRD measurement is estimated to be less than 0.0035. A small bowing in the variation of the alloy lattice constant with changing AlAs mole fraction is observed. The HRXRD characterized samples are used in Raman spectroscopy to calibrate the variation in the longitudinal optical (LO) GaAs and AlAs modes with varying alloy composition. Empirical expressions for the variation in the LO modes are found, with mole fraction errors of less than 0.03. Raman spectroscopy is a relatively simple nondestructive measurement and the expressions developed here allow for the fast determination of AlAs mole fraction in AlxGa1-xAs samples. The Raman data is compared to a theoretical dependence for a two phonon mode alloy crystal with excellent results.