I would like to build a entryway bench using a 3 foot length of 2 x 12. I plan to use 16" hairpin legs made of 1/2" cold rolled steel. Not sure if the type of wood matters, but I will probably use pine. How much weight can I expect the bench to hold?
I ran this through the sagulator, Assuming a shelf 36", 2x12 on side, supported at the ends (floating) with a center load of 1000 lbs, and got a total deflection of .07 inches.
1200 lbs still read as acceptable, 1250 went borderline.
So for supporting one or two humans within normal weight parameters, you should be good. I'd be more interested in the legs and how they are connected.
Unless you want to use a 2x12 for aesthetic reasons, it is way overkill. I just built a bench slightly longer than that with 2x8 and it doesn’t sag at all under adult weight. This may help decide on an appropriate width of 2x.
Or based on this load table I’d estimate 1500lbs