How many shares will be found for a given hashrate?
One difficulty-1 share takes on average 2^32 = 4.3 billion hashes to find.

If your hashrate is X GH/s, then in one day the number of difficulty-d shares you'll find is

(X * 1000000000 * 86400) / (2^32 * d)

Or simply

20,000 * X / d