No, you don't. This is naive. Human beings aren't computers.
There is no constant output per hour of work. It's nonsense. The output per hour of work depends entirely on the state of mind and physical condition of the employee.
If the employee is well-rested, healthy, and happy, they will be quite productive.
If they are sleep-deprived because they stayed at the office until midnight, depressed because they have nobody to share their life with, and physically exhausted or sick because they haven't taken time off in years ... you really think they will produce the same output as well-rested, happy employees? No. They won't even produce a quarter. In fact, they will make mistakes that will end up costing you on top of whatever it is that you're paying them.