Kat . . print this off or write it down and stuff it with your filter.

1/8000 = 1/8
1/4000 = 1/4
1/1000 = 1/2
1/500 = 2
1/250 = 4 .
1/125 = 8
1/60 = 16
1/30 = 30
1/15 = 60
1/8 = 120
1/4 = 240
1/2 = 480
1 = 960
2= 1920
4 = 384

First column is your meter reading using NO FILTER. The second column is the adjusted exposure you need to use.