why is it that sometimes when you are calculating volume there is one number behind the decimal point, but sometimes there is two?
There can be any number of digits after a decimal point, not just one or two. It all depends upon the dimensions of the item that you are calculating the volume of. If you are calculating the volume of a prism, this formula always works: volume = base * height, where the base is the surface area of the bottom or top of the prism.