# What's the mathematical formula for determining scale?

**URL:** <https://boards.straightdope.com/t/whats-the-mathematical-formula-for-determining-scale/206634>\
**Category:** Factual Questions\
**Created:** [October 10, 2003, 7:10am UTC](https://boards.straightdope.com/t/whats-the-mathematical-formula-for-determining-scale/206634 "2003-10-10T07:10:18Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Ranchoth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranchoth/32/1066_2.png) [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)\
**Post date:** [October 10, 2003, 7:10am UTC](https://boards.straightdope.com/t/whats-the-mathematical-formula-for-determining-scale/206634/1 "2003-10-10T07:10:18Z")

</div>

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,  
Ranchoth

---

<div class="post-metadata">

**Author:** ![don\_t\_ask](https://avatars.discourse-cdn.com/v4/letter/d/e68b1a/32.png) [@don\_t\_ask](https://boards.straightdope.com/u/don_t_ask)\
**Post date:** [October 10, 2003, 7:20am UTC](https://boards.straightdope.com/t/whats-the-mathematical-formula-for-determining-scale/206634/2 "2003-10-10T07:20:54Z")

</div>

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

If 3" = 250’  
1/2" = 41’ 8"

---

<div class="post-metadata">

**Author:** ![II\_Gyan\_II](https://avatars.discourse-cdn.com/v4/letter/i/bbe5ce/32.png) [@II\_Gyan\_II](https://boards.straightdope.com/u/II_Gyan_II)\
**Post date:** [October 10, 2003, 7:23am UTC](https://boards.straightdope.com/t/whats-the-mathematical-formula-for-determining-scale/206634/3 "2003-10-10T07:23:33Z")

</div>

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.