Converting Filter Factors  to f-Stops
Filter 
Factor
f/stops
Filter Factor f/stops
1x --
4x +2
1.2x +1/4
4.8x +2-1/4
1.25x +1/3
5x +2-1/3
1.4x +1/2
5.7x +2-1/2
1.6x +2/3
6.4x +2-2/3
1.7x +3/4
6.8x +2-3/4
2x +1
8x +3
2.4x +1-1/4
9.5x +3-1/4
2.5x  +1-1/3
10x +3-1/3
2.8x +1-1/2
11.4x +3-1/2
3.2x +1-2/3
13.5x +3-3/4
3.4x +1-3/4
16x +4