Abstract The method of transforming Global Positioning System (GPS) derived ellipsoidal heights to Australian Height Datum (AHD) heights using a gravimetric geoid model is presented. Relative carrier-phase GPS observations, made at AHD benchmarks, are used to estimate the accuracy with which the gravimetric geoid height is known in Western Australia. The amount of GPS data collected for such an analysis is an important consideration, because the integer ambiguities must be solved in order to determine accurate heights. Graphical and statistical comparisons are made for the GEM-T2, OSU91A, AUSGEOID91 and AUSGEOID93 gravimetric geoid models. It is shown that the AUSGEOID93 model is superior to its predecessor and the two global models upon which it is based. However, long and short wavelength errors appear to remain, which may be due to the geopotential model and omission of terrain data respectively.