THE 8:80 RULE
The " 8-80 " Rule This rule is used by most project managers as a guideline for determining whether an activity qualifies as a work package. The rule states that any work package that takes less than one day to complete ( 8hours ), may be too small, and consideration should be taken to combine with some additional work. Conversely, if a work package takes longer than two weeks ( 80 hours ) it is obviously too large, and consideration should be taken to be broken down into smaller work packages. If the project is scheduled to take 18-24 months to complete, you may want to consider work packages that are larger, like one month. The important objective here is you want to ascertain that a work package is completed on time. If it is not, you want to have enough time to recover and keep the project on schedule, delaying too long, you may not have the flexibility to put some extra people on the package to get it finished in time to save the schedule.