The formula to use for growth rate is change in volume divided by initial volume:
So the growth rate for a month would be: the volume for that month minus the volume for previous month divided by volume of the previous month. For example if cell A1 = volume for March and cell A2 = volume for April, then the April growth is (cellA2-cellA1)/cell A1. Similarly the growth rate for a year would be the volume for the year minus the volume for the previous year divided by the volume of previous year. You may want to convert these to a percentage.