Everyone has their own recipes for Limoncello and I'm curious to know how many lemons do you use per 750 ml of alcohol in your recipe ?

I don't have a specific number. It depends on the size of the lemons. I use the peelings from 2 pounds of lemons for each 750ml of 190 proof Everclear and let them steep for 3-4 weeks.

I use the zest of about 10 lemons but I use vodka (I don't believe that Everclear is legally purchased in NY).

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.

The lemons I can get are about 3 inches top to tail with a diameter of about 2 inches - perhaps 2.5 inches

But wouldn't weight be related more to the amount of juice in the lemon rather than the surface area of the zest? I don't drink a lot of lemon juice but if I use oranges - two oranges may be the same size but one that is full of juice may weigh twice the amount of the orange that has a thick pith (albedo), but the area of zest they both supply will be very similar. No?

Possibly. But if you are using lemons all from the same source and all picked at the same time, there shouldn't be much difference in the amount of juice and rind thickness. I think difference in size would make more difference in weight. Here are the Sorrento lemons off my tree. As you can see, some are much larger than others -- and definitely weighed more.

Took a while to find it, but did find a surface calculator for a prolate sphere. A lemon 3" by 2" wide has a surface area of 17 square inches A lemon 3" by 2.5" wide has a surface area of 22 square inches So 1/2 inch wider increases the surface area by almost 30% How about 3.5 by 2.5? Surface area is 25 square inches, just about 50% more than the 3" x 2" https://www.easycalculation.com/shapes/surface-area-of-prolate-spheroid.php

I used 50 lemons for 3.5 liters of 160 proof everclear. After 6 weeks we did some trials and the Mrs. said it wasn't lemony enough. Another 30 lemons went in and it sat in the everclear for another 6 weeks. I just filtered it last week and it is FULL of lemon flavor now!

I use lemon extract ...................simple process as most of you know with everkleer ,the simple syrup to taste.

No I use the extract made from the zest extraction sitting in Everkleer, for about a month or more. then add the extract to the simple syrup and what ever else I'm using as a volume maker.

So by extract, you mean the infused Everclear. I thought there was some commercial extract, like vanilla extract, that you buy at the store.

Your correct about the color there limes I think but you got the idea. Extruding the oils from the zest via the EverKleer gives you a real extract and can last for along time and is dense in flavors .