Grooves and furrows have been interpreted as grabens resulting from extension of Ganymede's lithosphere. Geologically reasonable estimate of the dip (90¿--60¿) and displacement (less than 1 km to a few hundred meters) of faults bounding grooves on Ganymede allow calculation of the extension and surface area increase (0.04-2%) required for the formation of all grooved terrain. The implied radius increase is thus limited between 0.02 and 1%; 1% planetary expansion is the maximum possible since formation of the grooved terrain began. Similar estimates for faults bounding furrows, the oldest preserved tectonic features of Ganymede, indicate a maximum surface area increase of ~0.5% for the best developed furrow system, which is located in Galileo Regio. If equivalent furrow systems existed on all of the cratered terrain, then a maximum of ~0.5% increase in surface area of Ganymede is possible after the formation of the lithosphere and prior to the formation of grooved terrain. Faults bounding simple graben originate at a subsurface mechanical discontinuity and propagate upwards, resulting in grabens with similar widths and similar spacings between members of a set. The depth to this mechanical discontinuity for furrows and grooves on Ganymede must give at least a minimum lithosphere thickness, because it is impossible for faults to originate and propagate upwards from a point below the lithosphere. Therefore the minimum lithosphere thickness on Ganymede is 5 km and 9 km (in Marius and Galileo Regiones, respectively) at the time of furrow formation and 4 km at the time of groove formation.