Here is a method from Epoxyworks: https://epoxyworks.com/index.php/estimating-epoxy-amounts/
Basically you need to figure out how many cubic inches of epoxy is required. When you mix up epoxy you can also figure out the cubic inches for that piece and determine how much epoxy is needed for just that pour. I made up an index card with the amounts of part 1 and part 2 needed for a variety of sizes of boat pieces. then I was already when it came time to mix up a batch. It made life much easier. I used a digital gram scale.
Then you should be very happy with this. Sometimes when I was pouring small quantities of epoxy, 20 or 30 grams for example it was easy to add a gram or two too much. Then I found it handy to have the corresponding amount of epoxy figured out so I could simply add the proper amount to keep it in ratio. Don't forget that the measurements for volume, ie, # of pumps, versus weight are different. Your epoxy brand should have that information. Instead of 2 to 1 it might be 2 to 1.44 check with them for exact info.
I use 20 oz. triax on the bottom of my boats and it takes a little over 1 gal of West resin using 207 hardener which is 3-1 ratio. 2-1 ratio epoxy will go a bit farther. Can't help you with the sides as I rarely glass the sides of boats with Meranti.
When I was building my boat, I was told that for 10 oz of cloth, I'd need 10 oz of resin. So if the bottom of a 16' boat uses 4 yards of 22 oz cloth - total 88 oz - I'd need 88 oz of resin+hardener. Hope that helps.