It definitely depends on the person doing the brazing. You can use as little as an inch, or as much as an entire stick on the same joint, depending on your technique, the cleanliness of the joint, and the percentage of silver in the rod. I would say I tend to use more than other techs, because I try hard to get the rod to get sucked into the joint, and then I try to slowly build a cap on top of that on almost all of the joints that I do. I also don't clean most of my joints, so I try to make up for it by using extra sil-foss.
If you take the time to properly prep all of the joints, and have a good technique, you can get away with using less rod, and cheaper rod (less silver).
Purpose of this question wasn't really to try to save money. (but who isn't?) it was really for my to make sure that I wouldn't end up screwing myself in bidding some of these bigger jobs that might take 20lb to 30lb of sil-fos. that could end up in a big cost to me. I'm sort of new at the commercial estimating and trying to prevent a problem before I have one. Thank you all with all the help with this! It's nice to see a forum community to come together so well. i have been on others for my classic car questions and its like polling teeth for help sometimes lol.