Calculation is the act of calculating, which is using math or logic to figure out a problem. If your calculation is correct, then you can wear you sister’s favorite dress and put it back before she gets home.
A calculation is a careful, thought-out activity. The first kind of calculation involves figuring out the answer to a problem in math — the kind you might use a calculator for. Calculation also refers to using logic to figure out a non-numerical problem. If you have a difficult decision to make — like deciding what college to attend — calculation is your friend. That kind of calculation is to thoroughly think something through and make plans.