How long does the penis need to be to reach g spot?

Penises and G-spots: As they say, "Anything more than a handful is a waste." Or is it, "Anything more than a handful goes to waste?" If we were measuring horses, a hand would be 4 inches, but we're not exactly measuring horses... and we shouldn't need to exactly measure anything here. Couples can focus on teamwork (instead of asking the penis to reach a quasi-mythical G-spot, ask them to reach one another).