KES Parent is correct, the total number applying is about 3,500 for all KE Grammar
To get a view of the real probability of getting a place at a specific KE grammar, taking into account those that apply to multiple schools or reject a place, it's best to look at the pass scores as those are directly related to the candidate percentile.
If you take the pass scores for the last successful candidate for the last 5 years and select the highest (worse case) score. (from the sticky post).
Add 1 to allow for distance factors.
Divide by 3 and round up (to get the rounded score per paper)
You can then compile the following table from Age Standardisation Stats:-
SCHOOL, TOTAL SCORE, AV SCORE, PERCENTILE, PROBABILITY
KECHB, 348, 116, 86th, 1:7.1
KEFW, 331, 111, 77th, 1:4.4
KECHG, 330, 110, 74th, 1:3.9
KEAston, 329, 110, 74th, 1:3.1
KEHG, 320, 107, 68th, 1:3.1
So 1 in 7 is about correct for KECHB but it's quite a bit lower for other schools