Where the count comes from
Studs on layout is the part everyone can do and half the people get wrong. On a 16 foot wall at 16 inches on center, the layout marks fall at 16, 32, 48 and so on up to 192 inches, and there is a stud at zero as well. That is 192 divided by 16, which is 12, plus one for the starting stud: 13. The plus one is not a fudge factor, it is the fence-post problem. Thirteen studs, twelve bays.
Everything after that is detailing, and detailing is where estimates diverge. This calculator uses these allowances:
| Item | Allowance used here | Why it varies |
|---|---|---|
| Outside corner | 2 extra studs | A three-stud corner adds two beyond the layout stud. A two-stud corner with drywall clips adds one. California corners vary again. |
| Partition tee | 2 extra studs | A full backer plus blocking. Ladder blocking uses scrap and can add none. |
| Each opening | +4, less the layout studs inside it | Two kings and two jacks. Wide openings take double jacks; some take none if the header bears on a post. |
| Cripples | One per layout mark inside the opening | Only above the header. Windows also need cripples below the sill, which this does not count. |
The honest range on a real wall is plus or minus about 10 percent against a framer's own takeoff, and more if your corners or window detailing differ from the assumptions above. Treat the number as an order quantity, not a cut list.
Stud length and why 92-5/8 exists
A stud does not run the full wall height. It sits on the bottom plate and carries the top plates, so its length is the wall height less the plate thickness. With a double top plate that is three plates at 1-1/2 inches each, or 4-1/2 inches total. For a nominal 8 foot wall the stud is 96 minus 4-1/2, which is 91-1/2 — except that the standard precut is 92-5/8, which produces a 97-1/8 inch rough ceiling. That extra height exists so two 4 foot sheets of drywall stack with a little relief at floor and ceiling instead of binding. Read the stud length this calculator gives you as the arithmetic answer for the height you entered, and buy precuts if you want the drywall to behave.
Plates, laps and what the linear footage misses
Plate stock is straightforward linear footage: one bottom plate the length of the wall, plus one or two top plates. The catch is that the second top plate must lap the first at every corner and intersection, so the joints in the two courses cannot stack. In practice that means cutting into good stock rather than using an offcut. The piece count above is a plain division of linear feet by stock length and does not allow for that, so on a long wall with several corners add a piece or two to what it tells you.
Single top plates are allowed in advanced framing but only when the layout stacks — studs, joists and trusses all landing on the same 24 inch grid, with metal ties at the joints. If you are not building to that discipline, use the double plate.
What this does not decide for you
Header size is the big one. This calculator will tally the board feet of whatever header you pick, but it has no idea what is above the opening, how far the roof spans onto that wall, or what the snow load is. Header sizing comes off a span table for your code and your species, or off a stamped drawing. Picking a 2x8 because it fits the wall cavity is how people end up with a sagging opening.
Also absent: fire blocking, let-in bracing or structural sheathing, hold-downs, and anything about shear walls. Those are decided by the building, not by the wall's length.
Questions people ask
How many studs for a 20 foot wall at 16 on center?
Sixteen on layout, then add for the detailing. The layout is 240 inches divided by 16, which is 15 bays, plus one stud, so 16. A wall with two outside corners adds four, and a single three-foot door adds four kings and jacks, removes the two layout studs inside the rough opening, and puts back two cripples over the header. That lands around 24 studs. The layout number is exact arithmetic; the rest depends on how you detail corners and openings, so order a few over rather than exactly.
Is 24 inch on center strong enough?
For a non-bearing interior partition, almost always. For a load-bearing exterior wall it depends on the wall height, the stud size and the load above, and most prescriptive code tables get you there with 2x6 rather than 2x4. Advanced framing is built at 24 on center on purpose, because it uses less lumber and leaves more cavity for insulation, but it only works when the whole structure stacks on the same grid and the sheathing and headers are detailed for it. Do not switch an existing 16 inch design to 24 without checking the span table, and note that 24 inch spacing also needs 5/8 drywall on ceilings to avoid sag.
Does the calculator include cripples under a window sill?
No, only cripples above the header. Sill cripples depend on how far the sill sits off the floor and whether the sill is doubled, neither of which is a field here. A rough rule for adding them yourself: one cripple per layout mark inside the opening width, same as above the header, plus the sill plate itself at the rough opening width plus three inches. For a typical window that is another two to four pieces and one sill per opening.
How do I turn board feet back into a shopping list?
You mostly do not — buy by the piece. Board feet is useful for comparing a framing package against a quote, for estimating weight and truck space, and for pricing when a yard quotes by the thousand board feet. To go the other way, divide the board footage by the board feet per lineal foot for that size (0.667 for 2x4, 1.0 for 2x6) to get lineal feet, then divide by your stock length and round up per item rather than in aggregate. The piece counts above are already the shopping list; the board foot total is there for the quote comparison.