The geometry of a bicycle frame is determined by the lengths of the various tubes (seat tube, top tube, head tube etc.) and the angles at which they are joined.
According to Paul Hillbrick, the critical aspects of frame geometry in relation to the fit of a bike are the seat tube angle, the head tube angle, the top tube length and the standover height (which will depend on the seat tube length, whether the top tube is horizontal or sloping and the height of the bottom bracket.)
Look up the geometry of a bike on a manufacturer's website and you should find measurements for each of these aspects. Often others will be included as well.