A K&N 6001 filter has the following Beta Ratio Specs:
10/20/30=2.1/21.7/1000
10/20/30 are the micron sizes of the particles tested.
2.1/21.7/1000 are the Beta Ratios for those particles.
To get the percentages from the Beta number, subtract 1 from the Beta number and divide by the Beta number and multiply by 100. Our 2.1 would then be: 2.1-1= 1.1/2.1= 0523 x 100= 52.3 percent. Because our numbers are rounded, we did not quite reach K&N's published Beta Ratios of 53.1 percent at 10 microns (20 micron= 95.4 percent and 30 micron = 99.9 percent). For quick reference, here are common Beta Ratios and corresponding efficiencies.
Beta Efficiency
2 50%
10 90%
20 95%
75 98.7%
100 99%
200 99.5%
1000 99.9%