Given 252 square feet and 37.1 foot wingspan.
The Aspect Ratio (AR) is 6.8.
Your model has a 60" wingspan. So you multiply the span by the AR and get 408 square inches. Not so tough.
Given the span and area, which are usually published, you can get the AR, which makes mode-sizing easy.
Uh...
Nope. And, unfortunately, nope.
AR is the area divided by the span
squared. For the given numbers, the Spit has an AR of 5.46 (which sounds a lot better than 6.8 -- the Spit just has stubbier wings than that).
Area is span squared divided by AR, so for a 60" span it's 3600 / 5.46, or 659 squares.
Pat and Mark and I are all giving you slightly different numbers because of rounding errors, but they're all close enough to 660 squares to make no nevermind.
I'm going to bang a drum here that I usually only bang on for junior (and senior) engineers: dimensional analysis would have caught this. Area is length * length, so if you carry your dimensions and get something other than you expect, you know that you've made a mistake. Ratios are usually dimensionless -- the aspect ratio certainly is. So if you divide 252
square feet by 37.1 feet you get 6.8
feet, and you know you absolutely positively can't have an aspect ratio. It's a pain to carry the dimensions in calculations like this, but the pain of getting a calculation wrong when you could have caught it can be many times worse if you actually go into production with the error in your design (think dead people, or crashed Mars rovers, or, worse, union sheetmetal fabricators giving you the eyeball).