Cargo Question

I feel kind of stupid asking this because A) it's likely already been answered somewhere and I just can't find it and B) it seems like a pretty mundane bit of inconsequential minutia but at the moment it's a detail that I need answered in order to fill in some background for a scenario.<br /><br />I'm trying to figure out how long it would take a mining ship to fill each unit of cargo space. In my case, I'm using a HS 20 mining vessel that is using a digger shuttle and an orbital processing lab. Do we have any hard-and-fast rules governing this sort of thing listed anywhere perchance?<br /><br />And am I correct in thinking that a ship's cargo units are the same as its hull size or is that different for freighters and mining ships?