There are 2^32 different possible hashes which give a difficulty 1 share, so on average:

seconds to generate a share = (2^32)/(hashrate in hashes per sec)

shares per minute = 60/(seconds to generate a share)

shares per hour = 60*(shares per minute)

Take this number, multiply by your expected payment per share (e.g. the current PPS rate for whichever pool) and you have BTC/hour.