Wing Loading is the weight divided by the wing area. The usual units we use are ounces per square foot so you'll need to multiple the weight by 16 and then divide the area by 144.

wt x 16 /(area/144)

If you work the constants out you get 2304. So if you divide the wing area in square inches by the weight in pounds, you can multiply by 2304 and get the wing loading.

Let's say you have a 10 lb airplane with 1000 sq. in.
10/1000 = .01
.01 x 2304 = 23.04 ounces per sq. ft.