Wood plank carrying capacity?

Question

What is the carrying capacity of different sizes of wood planks? Specifically was wondering the load that a 12x2 plank spanning five feet can support.

Answer 1

Is the plank horizontal or vertical (flat, or on edge)?  I suspect it makes a difference.  Notice that joists used in home construction are mounted on edge, not flat.

Google "Engineering Properties of Wood" and you might find a free e-book.  Just don't exceed the modulus of elasticity.

Answer 2

400 pounds in the center would be safe, but the plank would sag noticeably.  The load decreases in proportion to the length.  I.e., a ten foot span would carry 200 lbs.

If the load is distributed evenly over the length, then it can be doubled.

A one by 12  inch plank could hold about a quarter of the load, or 100 pounds on a 5 foot span, and 50 pounds on a ten foot span.

To calculate capacities of different size planks you have to know some  beam design theory.  There are probably tables that you could find on line, if you look awhile.  Possibly under 'timber design', 'wood deck design' or 'scaffold design'