That's how people use dice rolls for deducing a seed? They handle it differently based on the number they get? Then the formula from BlackHatCoiner makes sense, but it seems like a questionable way to create a seed. At that point just toss a coin or just use the dice as a 50/50 randomness; 0 bit for even and 1 for odd number on top.
A dice is slightly faster than a coin, because it produces 2 bits most of the time.