99 efficiency at 25 microns is what you can expect. Buckley says the only way a micron rating means anything is to use the filter efficiency numbers published by the manufacturer.

Mobil 1 M1 113a Extended Performance Oil Filter
Oil filter micron rating. Tests have shown that particles as large as 200 microns will pass through a nominally rated 10 micron filter. At 10 microns its 94 percent efficient. Both filters will essentially remove their respective percentages of particles 20 microns or larger in diameter including virtually all particles large enough to be visible to the naked eye. However 10 micron is still very small and can benefit many industries from oil to chemical plants because of their ability to filter so much. The motorcraft fl 500s oil filter took the top spot on our list of the best oil filters thanks in large part to its highly efficient filter media that helps to protect against engine wear by screening out abrasives such as carbon sand dust and bits of metal. Purolator classic oil filters are 975 percent efficient and purolator pureone filters are 999 percent efficient the highest efficiency ratings on the market.
Like the micron ratings lower than this 10 micron rated filters tend to clog quickly. Motorcraft fl 500s oil filter. Another common rating for filters is the absolute rating. For the fram ultra guard filter it is 99 percent efficient at 20 microns. With a 95 efficiency rating it doesnt perform quite as well as those units. A nominal rating is an arbitrary size value assigned to a filter by the manufacturer.
For example a nominal micron rating of 10 microns at 95 means that the filter media retains 95 of the particles that are 10 microns and larger. Nominal micron rating means that the filter can capture a given percentage of particles of the stated size. At an average cost of 4 to 5 frams standard oil filter is the cheapest filter in our lineup costing roughly half the price of the mobil 1 and royal purple options mentioned above. This rating filters a little less than the 5 micron rating. For example a filter with a micron rating of 25 will filter out contaminants of 25 microns or larger in size and a filter with a micron rating of 5 will filter out contaminants of 5 microns or larger in size. Filters with a 10 micron rating can remove some unseen materials from liquid but not bacteria or viruses.
An absolute rating gives the size. Because the nominal rating is arbitrary it has no value. A micron rating is used to indicate the ability of an oil filter to remove contaminants by the size of the particles that the filter will collect and retain. The shell of the oil filter is much thicker which gives it extra strength. Ratings are from amazon at the time of publication and can change. This filter efficiency rating is listed as a percentage.
Every filter features 100 micro glass media which ensures the best particle removal possible. Get superior particle removal and high performance from royal purples extended life oil filter.