There are four important sizes to consider when choosing an oil filter. The most important is the filter micron size. This is a rating that designates how large a particle can be that will pass through the filter. The larger the micron rating, the smaller the particle must be before it can get through. An article in Motor Oil World outlined an oil filter study conducted by General Motors using diesel engines. This study concluded that a quality filter with a good rating improved mileage by nearly one percent. The other three sizes are thread size, filter height and filter diameter.
Remove the oil filter and drain the oil into a catch pan. Use a ruler to measure the diameter of the screw hole on the old filter. Also, measure the filter threads with a thread gauge, according to metric or SAE (Society of Automotive Engineers) thread ratings.