There is described a combine harvester comprising a grain bin having a grain volume monitoring system. The grain volume monitoring system has at least one image capture device which monitors the level of grain in the grain bin, such that a calculation of the volume of grain in the grain bin can be determined. In particular, the image capture device monitors the height of sections of the grain pile, as well as the angle of repose of the grain pile, which are used to calculate the contained volume of grain. The calculated volume can be compared with pre-set volume limits to prevent spillage of grain when driving on an incline or over uneven terrain.