|The amount of hot air needed to be exhausted is dependant on the amount of hot air generated. |
All computers generate different amounts of hot air dependant on the work they are doing, the type of CPU it is using and the environmental conditions. Consequently such a figure would be meaningless and impossible to calculate.
The only information along those lines is hidden deep inside the particular specs issued by the CPU manufactures where it does have a lot to say about cooling.
But that only relates to temperatures and heat sinks but nothing about air flow because a CPU manufacture will have no idea of what motherboard or case their CPU is going to end up in.
Some fan manufactures do publish figures for their fans but make no differentiation between hot air and cold air as hot air expands so there will be a greater volume of hot air leaving the case than cooler entering it.
Generally speaking a 5 inch rear fan along with the PSU fan exhausting hot air at the rear is usually enough. I front intake fan is very rarely needed.