On average it takes about 140 passive candidate leads to get one hire. Sometimes this number can be as low as 20 or so, or even as high as 200, but the 140 seems to be the mean for cold calling experienced individual contributor and mid-management level candidates across a variety of industries. Besides differences between industries this number also varies because of differences in how well you manage the process, how good you get at finding alternative was to reach people, how effective you are at converting suspects into prospects, and how diplomatically you manage your hiring managers or clients. It breaks down like this:

• 1. You should be able to reach about 25% of the cold passive leads you attempt to contact. These are leads not candidates!
• Of those about 25% should be interested. These are the "so called" passive candidates (or in other words prospects who have no reason to be expecting your call) so most of them will just not be interested. However, the better you get at quickly establishing rapport the higher this percentage can go. Personally I've managed recruiters with ratios upwards of 50% here, that is to say one out of two connections with real live peopel turned into interested prospects.
• Of those interested, since these are highly targeted passive candidates (remember that you went seeking specifically for them), they are well qualified so about 50-60% should end up being submitted, and about 80% of those you submit for consideration should be accepted.  

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