Measure the ceiling area with a tape measure in the room you will install the fluorescent light fixtures.
Divide the length or width area by the light coverage from each fluorescent fixture. For example, if a light fixture claims it will provide four feet of lighted space, a room 20-foot wide needs five fixtures.
Plan for more light over work spaces. Lights should be more prevalent over a workbench in a garage rather than over the area you park your car.
Visit a local lighting store to see what types of fluorescent fixtures they offer. Compare your measurements with information they offer for planning your light fixture layout.