How stud layout works
Studs are laid out on center (O.C.): 16" O.C. means the center of each stud is 16" from the center of the next. Sheathing and drywall come in 48" and 96" lengths, which divide evenly by 16, 24 and 19.2. That's why those spacings exist: every sheet edge lands on the middle of a stud.
The catch is the first stud. It sits flush with the end of the wall, so its center is ¾" in from the end. If you just measured 16, 32, 48 from the end, your sheet edge at 48" would land ¾" off the stud's center. So framers pull the layout back by half a stud: the first mark is at 15¼", then 31¼", 47¼", and so on. The stud's edge goes on that line, and the 48" sheet edge lands right on the stud's center.
How many studs do I need?
For a straight wall: divide the length by the spacing, round down, and add one for the starting stud. Add one more if there's a leftover bay at the end. A 12'-6" wall at 16" O.C. is 150 ÷ 16 = 9.375, so 9 full bays + 1 + 1 = 11 studs. Then add:
- Corners: 2–3 extra studs per corner, depending on your corner style.
- Each window or door: a king and a jack stud on each side (4), plus cripples above and below.
- Intersecting walls: a ladder or 2 extra studs for backing.
- Waste: 10% or so for crowned, twisted or split stock.
Which spacing to use
- 16" O.C. is the default for most exterior and load-bearing walls.
- 24" O.C. works for many non-bearing interior walls and for advanced framing, where code and the design allow it. It uses fewer studs and leaves more room for insulation.
- 19.2" O.C. puts five studs in every 8 feet and is mostly used for floor joists.
FAQ
How do I calculate how many studs I need for a wall?
Convert the wall length to inches, divide by the spacing (16 or 24), round down, and add one. Add one more if there's a leftover gap at the end. Then add studs for corners, openings and backing, plus about 10% waste.
Why is the first stud mark at 15¼ inches?
Pulling the layout back by half a stud thickness (¾") means the center of each stud falls on an exact multiple of 16". That lets 4×8 sheathing and drywall edges land on the middle of a stud.
Is 24 inch stud spacing allowed?
Often, yes. The IRC allows 24" O.C. for many 2×6 bearing walls and most non-bearing walls, depending on wall height and the loads above. Check the stud spacing table in your local code (IRC Table R602.3(5)).
How much plate stock do I need?
For a standard wall with a double top plate and a single bottom plate, you need three times the wall length, plus extra for laps at splices and corners.