well i typed out a big long message, and then MN went down :(
Basically...
Work out as a percentage of hours the hours worked by your part time person per year as against a full time person.
eg
full time of 37.5 hrs per week x 52 weeks = 1950 hours
Example 1) part time of 26 hrs per week x 52 weeks = 1352 hours per year.
pro rata is 1352/1950x100 = 69.3%
Example 2) part time of 30 hrs per week x 36 weeks a year (term only) = 1080 hours
pro rate is 1080/1950x100 = 55.4%
A full time employee gets (as standard) say 20 days annual leave + 8 bank hols.
so (20+8) x 7.5 hrs(per day) = 210 hrs per year.
Using example 1 above the part time employee gets 69.3% of this being 145.5 hrs
Example 2 gets 55.4% being 116 hrs per year.
However if the employee is entitled to more you imply increase the relevant section
Eg an employee may be entitle to 5 additional days plus the extra bank holiday this year
nb there is an extra bank holiday next year too..
Full time would get 25 days + 9 bank holidays...
so (25+9) x 7.5 hrs = 255 hours
Example 1 would get 69.3% of this being 176.5 this year
Example 2 would get 55.4% being 141.25 hours this year
Hope that makes sense!