Lumber Calculator
Lumber for a wall is three purchases, not one: studs on a layout spacing, plates that run the full length, and stock long enough to reach the ceiling. Enter the wall and this gives you the piece count to hand the yard.
Buy about
— boards in total
- Studs: —
- Plate boards: — (— linear ft of plate)
- Stock length: — ft
- Board feet: —
How many studs do I need for a wall?
A 20 foot wall with studs 16 inches on center takes 16 studs. The arithmetic is 240 inches of wall divided by 16, which is 15 spaces, and 15 spaces need 16 studs because every space is bounded by a stud at each end. That closing stud is the one people forget, and on a four wall room it is four studs short.
So the formula is wall length in inches divided by the spacing, rounded up, plus one. Round up because a wall is never an exact multiple: 10 feet is 120 inches, 120 divided by 16 is 7.5, so you need 8 spaces and 9 studs.
Openings move the number in both directions. A 36 inch door at 16 inches on center covers two layout studs, and framing the opening back in takes four: two king studs running full height beside it and two jack studs under the header. The net gain is two per opening, not four. Adding four blind is how a wall with six windows ends up with a dozen leftover studs in the garage.
| Wall length | 16 in O.C. | 24 in O.C. | Plate boards at 8 ft |
|---|---|---|---|
| 8 ft | 7 | 5 | 3 |
| 10 ft | 9 | 6 | 6 |
| 12 ft | 10 | 7 | 6 |
| 16 ft | 13 | 9 | 6 |
| 20 ft | 16 | 11 | 9 |
| 24 ft | 19 | 13 | 9 |
| 30 ft | 24 | 16 | 12 |
| 40 ft | 31 | 21 | 15 |
16 inches on center or 24, and what the gap costs
Sixteen inches is the default for bearing walls and for anything that will carry tile, cabinets or a heavy mirror. Twenty four is legal for interior non-bearing walls, and it uses a third fewer studs: half a stud per foot instead of three quarters.
The saving tends to move into the drywall. On walls, half inch board is rated for 24 inch spacing, so nothing changes there. On ceilings it is not, and a 24 inch ceiling needs five eighths board, which is heavier per sheet and harder to hang alone. If you are working without a second pair of hands, that usually decides it before the stud count does.
Two other things 24 inches buys less of. Insulation at 24 inches doesn't change the R value of the cavity, but wider spacing means a wall that flexes more under a shoulder, which matters if the drywall is thin. And a wall with a vanity, a grab bar or a wall hung TV bolted to it wants a stud where the fastener lands, not 12 inches to either side.
Studs, plates and headers are three separate orders
Plates run the length of the wall and there are usually three runs: one bottom plate and a double top plate. The second top plate is not decoration on a bearing wall. It ties intersecting walls into the one you are building, and it lets you lap the joints so no two plate breaks land on the same stud.
Plate stock is bought long and cut once. A 20 foot wall with 8 foot boards takes 3 boards per run, so nine boards, and the drops are 4 feet long — long enough for blocking, too short for anything structural. That is why the calculator counts plate boards at stock length instead of converting 60 linear feet into some ideal number of pieces.
Headers are not 2x4 and are not in the stud count. A 36 inch door in a bearing wall needs a header sized off a span table, usually a double 2x8 or 2x10 depending on what sits above it. Those come in their own lengths and they are the one line item a stud calculator will always miss.
What length board to buy
Buy the shortest stock that covers the wall height: 8, 10, 12, 14 or 16 feet. A 9 foot wall needs 10 foot studs, and that is 25% more board feet per stud to gain 12 inches of length — you pay for the extra on every piece and cut most of it off.
| Wall height | Precut stud | Framed height |
|---|---|---|
| 8 ft | 92 5/8 in | 97 1/8 in |
| 9 ft | 104 5/8 in | 109 1/8 in |
| 10 ft | 116 5/8 in | 121 1/8 in |
Precuts exist because the plates eat length. A 92 5/8 inch stud plus four and a half inches of plates frames a wall that measures 97 1/8 inches to the top of the top plate, not 96. Buy 8 foot studs instead and the wall comes out an inch and a half tall, which shows up as a gap at the ceiling or a fight with the door frame.
Grade matters more than length. Stud grade is fine for a non-bearing partition. Anything carrying a load wants number 2 or better, which is straighter and dries harder. Framing lumber also shrinks as it dries, so buy it a week before you frame and let it sit flat and stickered — a wall built from green studs crowns and pops drywall screws by winter.
Board feet, and why a 2x4 is not 2x4
Board feet is nominal thickness times nominal width times length in feet, divided by 12. A 2x4x8 is 2 x 4 x 8 / 12 = 5.33 board feet, even though the piece in your hand measures 1.5 by 3.5 inches. The nominal number is what the price is built on.
| Nominal | Actual (in) | Board ft / ft |
|---|---|---|
| 1x4 | 3/4 x 3 1/2 | 0.33 |
| 2x4 | 1 1/2 x 3 1/2 | 0.67 |
| 2x6 | 1 1/2 x 5 1/2 | 1.00 |
| 2x8 | 1 1/2 x 7 1/4 | 1.33 |
| 2x10 | 1 1/2 x 9 1/4 | 1.67 |
| 2x12 | 1 1/2 x 11 1/4 | 2.00 |
| 4x4 | 3 1/2 x 3 1/2 | 1.33 |
| 6x6 | 5 1/2 x 5 1/2 | 3.00 |
Framing lumber is sold by the piece, not the board foot, so this only matters when you price rough sawn hardwood or order from a mill. If a quote comes back in board feet and your takeoff is in pieces, the two numbers will never agree and neither one is wrong — one is measuring wood, the other is counting boards you can carry.
Where the waste actually goes
Ten percent is normal on a wall. Five percent is possible on a plain rectangle where you can reuse drops, and fifteen is more honest on a wall with six openings, because every opening generates cripples and trimmers that come out of short scraps you may not be able to reuse.
The bigger waste is not the saw blade, it is the plate layout. A 20 foot wall built from 8 foot boards throws away 4 feet on every third board, and a 24 foot wall at 12 foot stock has no waste at all on plates. Matching stock length to wall length is worth more than trimming the waste percentage by two points.
Lumber calculator FAQ
How many 2x4 studs do I need for a 10 foot wall?
Nine studs at 16 inches on center, and six plate boards if you buy 8 foot stock. The studs come from 120 inches divided by 16, which is 7.5 spaces rounded up to 8, plus the closing stud at the end. The plates are three runs of 10 feet, and each run takes two 8 foot boards. Add 10% waste and you carry 10 studs and 6 plates.
How many studs are in a 24 foot wall?
Nineteen at 16 inches on center, thirteen at 24 inches. The count is the wall length in inches divided by the spacing, rounded up, plus one. Twenty-eight feet of plates at 8 foot stock adds 12 boards, three per run.
Should I use 16 inch or 24 inch stud spacing?
Sixteen inches for bearing walls, walls that carry tile or cabinets, and anything you might hang a shelf from. Twenty-four inches is code for interior non-bearing walls and uses a third fewer studs, but a 24 inch ceiling needs 5/8 inch drywall instead of 1/2 inch, so part of the saving goes into the board.
Do I count corner studs separately?
Yes. The layout spacing puts one stud at each end of a wall, but a corner where two walls meet needs a third stud so both walls have something to nail their drywall to. Count one extra stud per outside corner and per wall intersection.
How much lumber do I need to frame a 12x12 room?
About 40 studs and 18 plate boards of 8 foot stock, before openings and waste. Each of the four walls is 12 feet long, which is 10 studs at 16 inches on center; the four shared corners reuse studs rather than adding them, so the total lands near 40 rather than 44. Subtract the layout studs your doors and windows cover, add four per opening, then add 10%.
What is a precut stud?
A stud cut at the mill to a length that builds a specific wall height: 92 5/8 inches for an 8 foot wall, 104 5/8 for 9 foot, 116 5/8 for 10 foot. Add the 4 1/2 inches of plates and a precut 92 5/8 stud frames a wall that measures 97 1/8 inches, or 8 feet 1 inch, to the top of the top plate.
How many board feet is a 2x4x8?
Five and a third board feet, using nominal dimensions. Board feet is thickness times width times length in feet, divided by 12, so a 2x4x8 is 2 x 4 x 8 / 12 = 5.33. The piece actually measures 1.5 by 3.5 inches, so you are paying for 5.33 board feet of nominal lumber that contains about 3.5 board feet of wood.
Do I need a double top plate?
On any bearing wall, yes. The second plate ties intersecting walls to the one you are building and lets you lap the joints, so no two plate breaks land on the same stud. A single top plate is allowed on some non-bearing partitions, which is where the three-run count drops to two.
Where these numbers come from
Stud counts follow the layout rule in the code: studs at a maximum spacing, one at each end of the wall, doubled or tripled where walls meet and where openings are framed.
- International Code Council — IRC wall framing spacing, top plate and drywall thickness tables adopted by most US jurisdictions
- American Wood Council — span tables for headers and joists, and the sizing that a stud calculator does not cover
- Western Wood Products Association — nominal and dressed dimensions, and lumber grading rules
- USDA Forest Products Laboratory — Wood Handbook data on shrinkage and moisture content
Local amendments change spacing and bracing requirements, and wind and seismic zones add hardware this page does not count. Check with your building department before you frame.
Related calculators
Last updated: 2026-10-29