Lumber Calculator
Stud counts that include the corners, kings, jacks and cripples.
Getting your lumber order right
A wall needs far more studs than length divided by spacing. Corners, kings, jacks and openings all add pieces.
Why the stud count is always higher than you expect
Take a twenty-four foot wall at sixteen inch centres. Divide and add one and you get nineteen studs. Then start building it.
Each corner takes three studs rather than one, so that is four more. Every window and door needs a king stud and a jack stud on both sides, which is four pieces per opening, twelve across a door and two windows. What comes back off the total is the handful of studs that would have landed inside the openings, because those do not get framed — about six of them on a wall like this.
Nineteen becomes twenty-nine, and thirty-two once you allow ten percent for culls. Then there are ten cripples above the headers and under the sills, cut from offcuts rather than bought.
Ten pieces is a wasted trip to the yard at four in the afternoon, and it is the number this calculator is built to get right.
Nominal size and actual size are different numbers
A 2x4 has not measured two inches by four since it was rough-sawn. Surfaced and dried, it is one and a half by three and a half.
Which number you use depends on what you are doing. Anything you are fitting into a space — stud bays, headers, cavity depths — uses the actual dimension. Board feet, which is how lumber is priced and sold in volume, uses the nominal one. The calculator uses nominal for board feet and actual everywhere else, which is the convention the yard works to.
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FAQFrequently asked questions
Start with the wall length divided by your stud spacing, plus one for the end. Then add two studs at each corner, four per opening for the kings and jacks, and take off the studs that would have fallen inside the openings, because those do not get framed. Cripples go above each header and below each window sill, usually cut from offcuts. A wall with a few openings needs considerably more than the spacing calculation alone suggests.
At sixteen inch centres a plain ten foot wall takes nine studs including the end one. Add a three foot window and it goes to eleven full-length pieces, because the two kings and two jacks come on and the two studs that would have sat inside the opening come off, plus four short cripples above and below. Enter your wall and openings above for the real number.
Multiply nominal thickness in inches by nominal width in inches by length in feet, then divide by twelve. The nominal size is the important part: a 2x4 counts as two by four even though it measures one and a half by three and a half.
Nominal is the name, actual is the measurement. A 2x4 measures one and a half inches by three and a half, a 2x6 measures one and a half by five and a half. Use actual dimensions when fitting lumber into a space and nominal when calculating board feet.
Sixteen inches on centre is the common default. The code table allows twenty-four inch centres for 2x4 studs in a wall carrying only a roof and ceiling, and tightens to sixteen once the wall carries a floor as well, or if the studs are a lower grade. Twelve inch centres are used where extra strength is wanted. Your load path and your local code decide which applies, not preference.
Two. The code requires wood stud walls to be capped with a double top plate, and a single plate is only allowed if the splices, corners and wall intersections are tied with steel plates and the rafters or joists land over the studs. With one bottom plate that means plate material of three times the wall length, which is the part of a lumber order people most often under-buy.
A king stud runs full height beside an opening. A jack stud sits against it, cut shorter, and carries the header. Cripples are the short studs filling the space above a header and below a window sill. Every opening needs two kings and two jacks, plus cripples, which is why openings add so much to a stud count.
Around ten percent is a common allowance. Some of it covers cutting waste and some covers pieces you reject on sight — bowed, twisted or badly crowned boards that are not worth framing with. The allowance above is editable if your supplier's stock is better or worse than average.