Calculation Utilization Rate For Human Resources

Hi All,
I have been asked to calculate the utilization rate for human resource.
According to my knowledge i have done as below :
Standard Working Hrs : 40 hrs * 52 weeks in a year = 2080 hrs
Billable Resource : 10
Actual Working Hrs : No of working days*8 hrs
So it will be : 2080 hrs*10/Actual working Hrs
My question is if i take standatrd working hr in a day as 8 hrs to calculate the actual working hrs,the utilization rate will be correct ? according to my view it is not coz as the resource are working more than 8 hrs in day it wont be fair enough to calculate the actual hrs.
Also i have been asked to work out for per month.
So pls help me out in traceing this query.Its very urgent.

Dear Janaki,
Your projection on utilisation is correct.
but, rate of human utilaisation is depends upon the various technical issues on the floor. But all the times we con't consider those issues. For records one method should be follwed.
regards,
Vijay

Hi,
Resource Utilization Factor = (actual hours spent by the resource)/(Total Capacity Hours)*100
For Eg:
By considering, 8 Hrs/day with 22 working days for a month and 5 people worked on the projects.
If 2 out of 5 people always works 2 hours extra every day, then the utilization will be as follow:
RUF=((5*8*22)+(2*2*22))/(5*8*22)*100 = 110 %
If 3 out of 5 people always works 1 hour Less every day, then the utilization will be as follow:
RUF=((5*8*22)-(3*1*22))/(5*8*22)*100 = 92.5 %
Note: Actual effort should be accurate value
Leaves and Holidays to excluded from the capacity hours