(L x W) x 1.5 = Wattage 

Take the length of the room times the width of the room in feet and then times that number by 1.5.

 

(L x W) x 2.5 = Wattage

Much like the formula above take the length times the width of the room in feet, but instead of multiplying times 1.5 try 2.5. That should give you the right intensity for any reading, writing or fine detail work like chopping or sewing. The best form of task lighting will come from sources like lamps, hanging pendants, or spot lights.  

All fixtures hung from the ceiling excluding eating areas should be hung at least 7' off the floor. Sconces can be added to any room for extra lighting and ambiance. They should be mounted 60" off the floor and mounted no closer than 6-8 feet apart.

To find the right sizing for an entryway add the length of the room by the width and height of the room in feet. That number is the number in inches that the size of the fixture should be.

L + W + H = Fixture size in inches

A dining room chandelier should be no wider than 12 inches less the width of the table and should sit 30" above the top of the table for a standard 8' ceiling. Raise the fixture 3" for each additional foot of ceiling height.