Consider the size of the ceiling. Small ceilings should have recessed lighting with trims that are 3 to 4 inches in diameter, while large ceilings need larger lights that have a diameter of 6 to 8 inches.
Determine how high your ceilings are. The higher the ceiling, the larger the lights should be. Ceilings that are 12 feet high should have lights that are at least 6 inches in diameter, while 8-foot ceilings can get away with 4-inch lights.
Compare the two factors to determine the lighting size. For example, if your ceiling is large and high, you will want recessed lighting that is 8 inches in diameter. Ceiling that is low and small needs only 3-inch diameters. If you have something in the middle, such as a low, large ceiling, use 5-inch lights.
Position lights 3 feet apart if you have 8-foot ceilings, 4 feet apart for 10-foot ceilings and 5 feet apart for 12-foot ceilings.