What's the mathematical formula for determining scale?

If you’ll forgive me, one of 8 nerd worldwide who’s lousy at math, asking a dumb question…what’s the mathematical formula for determining the “scale” of a drawing or photo?

Say, I have a drawing of an aircraft. I know the aircraft to be 250 ft. long in real life, and the drawing of it is 3" long. If the drawing is, say, half an inch wide, how do I figure out how wide the actual aircraft is?

Well, thanks for your time,

Well 1/2 an inch is 1/6 of 3 inches.

If 3" = 250’
1/2" = 41’ 8"

The math you’ll be using is ratio & proportion.

If 250’ = 3" on paper, 0.5" on paper is (0.5/3) *250’ in real life --> 41.67 ft.

But, this assumes a “non-tilted” view of the plane i.e. direct view of the topside or the underside. Else, you would need to know the angles and do some co-ordinate transformations.