We present a detailed study of compressively strained PbxSr1−xTiO3 thin films grown by off-axis radio frequency magnetron sputtering on (001)-oriented Nb-doped SrTiO3 substrates. Film tetragonality and the ferroelectric critical temperatures are measured for samples of different composition and thickness and compared with a phenomenological Landau-Devonshire model. 180∘ ferroelectric domains are observed using both X-ray diffraction and piezoresponse force microscopy and domain sizes obtained by the two techniques are compared and discussed.