how do you calculate how much cement will be used per feet on a construction?

Take your measurements to the place where you are buying the cement (or are you referring to concrete?). They will tell you how many bags you need. And yes, there are standard volume formulas used, but you don't really need them, there are various calculator sites. Just google "concrete calculator". Good luck with your project

Dude I don't want to be disrespectful, but and a big but for what purpose? You will need to do different calculations for cement for different applications.

There is a formula for cement to make concrete, another formula for mixing mortar for laying bricks, blocks and stone, there is another formula for cement rendering, another to form a dry screed to lay tiles on. Your question is very simplistic, the meaning of simplistic, Treating complex issues and problems as if they were much simpler than they really are.

Concrete used for slabs is usually calculated in cubic yards. Measure length times width times depth. If measurements were in feet, divide by 27 to get cubic yards. Add a half yard in calculations for spillage, irregularities, and just because it's better to have a little too much than just not enough.

length * width * depth