I live and work in Florida. I was hired by a company and paid a salary of $535.00 per week for 45 hours,although I always worked more hours than that my pay stubs always showed I worked 40 hours. About a year later I was converted to hourly. My new hourly rate was computed as follows, $11.27x40 hours=$450.80,5 hoursx$16.91=$84.55 for a total of $535.00.
My question is was this legal for him to compute my hourly rate this way,as my salary was based on 45 hours with no overtime ever paid? Should the $535.00 have been based on 40 hours? Would the "fluxuating work week" enter into this?

The employer can convert it any way they determine. There is no law regarding this.

As to the "fluctuating work week" pay method, while you were on salary, that can only be used when the hours regularly vary above and below 40 hours per week. In addition, you still must be paid overtime based on the "regular rate of pay" for all hours over 40 in a workweek.

What you might be talking about is a Belo-plan, wherein the salary is for a stated number of hours (not to exceed 60). To qualify the plan must:
1. agreed to by the employee through and individual contract or collective bargaining agreement;
2. the employee must work irregular hours (again, with workweeks fluctuating above and below 40 hours);
3. the contract must guarantee a straight-time rte of at least the statutory minimum wage and an overtime rate of at least 1.5 times the regular rate of pay (as the FLSA defines it); and
4. the weekly guarantee must be for not more than 60 hours per week.

A Belo plan 7(f) must also be approve by US DOL in Wash DC...