Instead of creating a spreadsheet for scaling up from your reference you can get what is called a "proportion wheel". It does the calculations for you and has been used by illustrators for decades.
Another useful measuring device is a pair of calipers. This is especially helpful if you blow your reference up to painting size. You can measure the distance between the eyes on the reference and then move the calipers over to the painting. You don't even have to make a mental note that it's 17/20ths of an inch or anything like that.
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