I'm just curious about this. I'm not sure if the length of zeros in the hash result is directly proportional to the probability, or how to calculate this.
(Average hashing power of network per second between the last difficulty adjustment and the difficulty adjustment that came before it) * 600
or (2^32 * difficulty)
As relative Answer in terms of Coins per day:
A B coins = reward / (difficulty * 4294967296 / hashsPerSec / 3600 / 24)
A is the number of seconds in an hour
B is the number hours in a day