Usually three 12 hour shifts/week, so annual salary needs to be calculated based on a 36 hour work week, not 40. This is a little accounting trick that saves hospitals money. Where the traditional 40 hour work week still exists, the hourly salary is usually less than 36 hour per week salaries, but the actual annual salary is more because you get paid for a full 40 hours per week.

For example:

$28/hr X 40 hrs/week X 52 weeks = $58,240/year

$30/hr X 36 hrs/week X 52 weeks = $56,160/year

$31/hour X 36hrs/week X 52 weeks = $58,032/year

Bear in mind that you also have to factor in differentials for evenings, nights and weekends to get a true picture of the annual salary.