From the Hotline: Calculating FMLA leave

Question: The federal Family and Medical Leave Act (FMLA) refers to 12 weeks, but if someone is out seven working days (one week and two days), how would that be calculated? How would that be designated?

Answer: Employers may convert the amount of time available for Family and Medical Leave Act (FMLA) to hours for these types of situations.

For example, if an employee normally works eight hours per day, five days per week, this would amount to 480 hours over 12 weeks (8 x 5 x 12). Alternately, if someone works four hours a day for four days a week, their allocation would be 192 hours (4 x 4 x 12). Using this method, you can determine the total hours that this employee originally had available, and then deduct the number of hours used, to determine what the employee has remaining. This amount is what you would communicate to the employee regarding current available time.

Source: http://www.dol.gov/whd/opinion/FMLA/2002_05_09_1_FMLA.htm