[make] a calculation

to determine a value through mathematical means

He needed to make a calculation to estimate the project's total cost.
She made a calculation to estimate how much paint would be needed for the room.
Let me make a calculation to figure out the total cost of the project.
He made a calculation to find out how much money he would save by switching to a cheaper phone plan.
Let's make a calculation to see how many guests we can accommodate at the party.