depends on if you have cabinets /fridges/ dishwashers etc under it too and if you want seating at the bar etc !
24" or 600mm seems to be standard for cabinet coverage in a lot of countries - then overhang could be 8-12" or 200- 300mm either at the same height or higher or lower than the bar area .
why not add a sketch plan of the space you have and what you'd thought of so far ?!