Require data as percentage based on a calculated column

Require data as percentage based on a calculated column

Hi, my Base Data looks like this:
SRID  StoreID Availability
1          A           1
1          B           0
2          C           1
1          D           1

I want this output
SR  #ofStores   Availability
1         3                 66%
2         1                 100%

I have been able to work out the #ofStores as Count of SRID. But I'm unable to figure out how to calculate a percentage on a calculate field - #ofStores. I can get counts in Availability (2 for SRID 1 and 1 for SRID 2). How do I calculate it as a %age of #ofStores?