There is debate about this. The US flag is based on the Grand Union Flag (also known as the continental flag).

It seems very likely that the Grand Union Flag was copied from the East India Company's flag. It is plausible that this was simply because it was easy to adapt the British naval ensigns that would have been flown by most of the ships - by adding white stripes to the red. It is also possible that it was chosen to represent an 'imperial British' identity (as opposed to a 'home British') - as the EIC flag was one of the most pervasive symbols of global Britishness. This is consistent with early hopes by the rebels that they would be able to reunite with Britain.