It makes a huge difference based on what alcohol you are using.
190 proof Everclear, like I said, peeling from 2 pounds.
151 proof Everclear, I would up the lemons to 3 pounds and let steep for 4 weeks
100 proof vodka, I would stuff as many peelings into the steeping jar as I could and let it steep for 6 weeks.
I use pounds of lemons rather than number of lemons, because there can be a big difference in size. My 7 Sorrento lemons weighed in at 3 pounds total, and 4 of those lemons were 2 pounds total. They do get pretty big. Had to cut those 4 into 1/8ths to squeeze them.