1 muffin = 1/4 cup of batter
2 muffin = 2/4 cup of batter (or 1/2)
3 muffin = 3/4 cup of batter
4 muffins = 4/4 cup of batter (or 1 cup)
5 muffins = 5/4 cups of batter (or 1 and 1/4 cups)
6 muffins = 6/4 (or 1 and 2/4 cups) (or 1 and 1/2 cups)
and it keeps going
hope it helps!