Count wood studs and plate lumber for a framed wall from its length and spacing.
Studs = wall length ÷ spacing + 1. Plates run the full wall length once per plate. A common rule adds 3 studs per corner and 2 per opening for kings and jacks, on top of this straight-run count.
At 16" on center: 12 ÷ 1.333 = 9, plus 1 = 10 studs, before corners and openings.
That's a rough rule of thumb that includes corners, openings and waste. The straight-run count at 16" o.c. is 0.75 per foot plus one.
Stud count doesn't change with size; 2x6 is common for exterior walls (more insulation) and 2x4 for interior partitions.
Doing it from plans instead? Read Wood framing takeoff from plans, or see all free takeoff calculators.