All you have to do is divide by the numerator (the top number) by its denominator (the bottom number). Example. If you want to convert 3/8 into a decimal, divide 3 by 8.1. Because 8 can't go into 3, you have to add a zero to 3, making it 30. And you also have to make sure that you do all you're math correctly so that you get it correct!