How many studs do I need for a 20 ft wall?

18 at 16 in on center, for a wall with one opening. The 20 ft run is 240 in, which is 15 bays, plus one stud at the end, plus two for the opening. At 24 in on center the same wall takes 13. If the wall has no openings at all it is 16 studs at 16 in — the difference between that and 18 is the pair this page adds for the header.

Why does the count not match my layout?

Because of the two studs per opening. A real layout displaces the studs a window sits on and adds jack and king studs in their place, so a 3 ft window at 16 in on center changes the count by nothing on the plan while this page adds two. That is deliberate: the two directions are not symmetric. Counting one stud too many costs a couple of dollars; counting one too few stops the job while somebody drives to the yard. Use the number to buy, and your layout to cut.

What is a board foot?

It is the North American unit for pricing lumber: one board foot is a nominal 1 in × 12 in × 12 in, so a 2×4 is 0.667 board feet per foot and a 2×6 is 1. It is calculated from nominal sizes, which is the trade convention and not a mistake — the actual volume of a 2×4 is about 0.44 board feet per foot, so the figure on this page is roughly 50% more than the wood, and it is also not a weight.

16 in or 24 in on center?

16 in is the residential default and the spacing most tables assume; 24 in saves studs and is common on non-bearing walls and on walls with thick enough sheathing to span it. The rule of thumb is that a bearing wall carrying a floor above stays at 16 in unless a span table says otherwise for your stud size. On the page the choice is a field, so you can price both: on a 40 ft wall the difference is ten studs.

How much top plate do I need?

Three runs of the wall length: one sole plate and a doubled top plate, which is the usual build for a bearing wall and what the plate figure reports. A partition wall that carries nothing above it is normally built with two runs, so multiply the plate linear feet by two thirds. The plate is reported separately from the studs because it is a different length — it runs with the wall, not up it — and it is the same lumber.

Does the wall height change the stud count?

No, and that catches people out. Height is eight feet in most houses and the studs are bought at that length, so it changes the stud linear feet and the board feet but not the number of pieces — a taller wall takes the same studs, each one longer. What does change the count is spacing and openings. If you are framing a wall over 10 ft, the studs become a special order and the price per piece steps up.

Framing Calculator

Result

Studs

Stud length in feet: 144 ft
Plate length in feet: 60 ft
Board feet: 136 bf

Framing calculator: work out how many studs a wall takes, how much plate goes with them and how many board feet that comes to, from the wall length, the height and the stud spacing. Stud spacing decides almost everything: a 20 ft wall at 16 inch on center has 15 bays and takes 18 studs once the end stud and one opening are counted, and the same wall at 24 in on center drops to 13. The count is bays rounded up, plus one for the end, plus two for every opening — the extra two are a rule of thumb for the jack and king studs that carry a header, and they are added without subtracting the studs the opening displaces, so a wall with a window in it comes out two studs heavier than a precise layout would. The page then reports the same batch of lumber four ways, because they are four different ways to buy it: studs by the piece, studs and plates by linear feet, and board feet — the North American trade unit, which for wall framing is calculated from nominal sizes, so a 2×4 reads 0.667 board feet per foot against an actual volume of 0.4375. The defaults, a 20 ft by 8 ft wall at 16 in on center with one opening, come to 18 studs of 2×4, 144 ft of stud and 60 ft of plate — three runs of the wall length, one sole plate and a doubled top plate.

Stud count and board feet per 8 ft of wall, by spacing

Stud spacing	Studs per 8 ft wall	Board feet per 8 ft wall (2×4)
16 in on center	7	37.33
24 in on center	5	26.67
400 mm on center	8	42.67
600 mm on center	6	32

Counts are for an 8 ft length of wall, 8 ft high, with no openings, and the board feet cover the studs only — the plate for an 8 ft wall is another 24 ft of lumber, or 16 board feet of 2×4. Read the rows in pairs: 16 in and 400 mm are the same spacing in two measurement systems, so they differ by one stud only because 400 mm is slightly tighter than 16 in. Board feet are calculated from nominal sizes, so the third column runs about 50% above the actual volume of the wood.

Formula

studs = ceil( wall length ÷ stud spacing ) + 1 + openings × 2 stud linear feet = studs × height plate linear feet = wall length × 3 board feet = board feet per foot × ( stud + plate linear feet )

L: Wall length, in feet
H: Wall height, in feet — usually the ceiling height, since studs run from the sole plate to the top plate
s: Stud spacing on center, in inches (16 in is the usual residential value, 24 in the cheaper alternative)
openings: Number of doors and windows in the wall — each one adds two studs for the header
plates: Linear feet of plate, counted as three runs: one sole plate and a doubled top plate
board feet: Volume in board feet, calculated from nominal sizes rather than actual ones — the trade convention

Use it once the wall is laid out on the floor, because the stud spacing is a decision rather than a measurement: 16 in on center is the residential default and the value most tables are written for, 24 in saves studs and needs thicker sheathing, and a bearing wall carrying a floor above should not go past 24 in without checking a span table. Count the openings first — a door and a window each cost two extra studs, and the header itself is not part of this page. Then read the four outputs as four shopping lists: buy studs by the piece and by length from the height, buy plate by the run, and if your supplier quotes board feet, that is the last row. For an interior partition wall that does not carry a load, count two plate runs instead of three and multiply the plate figure by two thirds.

Worked examples

A 20 ft × 8 ft wall at 16 in on center, one opening
1. Bays: 20 ft is 240 in, and 240 ÷ 16 = 15 exactly, so 15 bays
2. Studs: 15 + 1 end stud + 1 opening × 2 = 18
3. Stud linear feet: 18 × 8 ft of wall height = 144 ft
4. Plate: 20 ft × 3 runs = 60 ft
5. Board feet: 2×4 is 0.667 bf per foot, so (144 + 60) × 0.667 = 136 bf
The defaults, and the wall divides evenly — 15 bays, no short one at the end. The 18 studs are worth reading against a precise layout: a 3 ft window at 16 in on center displaces two studs and needs two at its edges, so on a real layout the change is nothing, and a framer laying it out on the deck would cut 16 studs where this page's rule of thumb counts 18. Those two extra studs are the delivery you do not have to make twice.
A 16 ft × 8 ft wall with no openings
1. Bays: 16 ft is 192 in, and 192 ÷ 16 = 12 exactly
2. Studs: 12 + 1 = 13, with nothing added for openings
3. Stud linear feet: 13 × 8 = 104 ft
4. Plate: 16 × 3 = 48 ft
5. Board feet: (104 + 48) × 0.667 = 101.33, reported as 101
Zero openings is a legal input, unlike the other four fields, which is why this example exists. Note the board feet: 101.33 is reported as 101 rather than 102, because board feet are a price figure rather than a count of pieces — you are not buying 102 of anything. If your supplier rounds it up to the next board foot, the difference is a few cents.
A 40 ft × 10 ft wall at 24 in on center, 2×6 studs, three openings
1. Bays: 40 ft is 480 in, and 480 ÷ 24 = 20 exactly
2. Studs: 20 + 1 + 3 openings × 2 = 27
3. Stud linear feet: 27 × 10 = 270 ft
4. Plate: 40 × 3 = 120 ft
5. Board feet: 2×6 is 1 bf per foot, so 270 + 120 = 390 bf
The same wall in 2×4 would read 260 board feet instead of 390, for identical lengths — board feet are a function of the nominal size, so a deeper stud costs more per foot even when nothing about the wall geometry changed. Read the stud count too: 24 in on center saves ten studs against 16 in on the same run, which is most of why it is popular, and it is also why the sheathing has to be thicker.

Limitations

This page counts material and does not design the wall. It does not check whether a stud size or a spacing is adequate — 24 in on center with 2×4 studs is fine for a partition and wrong for a two-storey bearing wall, and this page will happily count either. It does not size headers, does not count jack and king studs as a real layout would, and does not know about blocking, let-in bracing, shear nailing or any of the details an inspector looks at. The rule of thumb of two extra studs per opening is added without subtracting the studs the opening displaces, so a wall with openings reads high, deliberately: running short on a framing day means a trip to the yard, and one spare stud costs almost nothing. The count of openings has to come from you — the page never sees a drawing. Plate is counted as three runs, which is right for a bearing wall and one run too many for a partition. Board feet are calculated from nominal sizes per trade convention, so they are about 50% higher than the actual volume of wood for a 2×4 and they are not a weight. Finally, the counts assume every stud is full height: a wall with a header over a wide opening has shorter studs above it, and those are not modelled.

Frequently asked questions

How many studs do I need for a 20 ft wall?: 18 at 16 in on center, for a wall with one opening. The 20 ft run is 240 in, which is 15 bays, plus one stud at the end, plus two for the opening. At 24 in on center the same wall takes 13. If the wall has no openings at all it is 16 studs at 16 in — the difference between that and 18 is the pair this page adds for the header.
Why does the count not match my layout?: Because of the two studs per opening. A real layout displaces the studs a window sits on and adds jack and king studs in their place, so a 3 ft window at 16 in on center changes the count by nothing on the plan while this page adds two. That is deliberate: the two directions are not symmetric. Counting one stud too many costs a couple of dollars; counting one too few stops the job while somebody drives to the yard. Use the number to buy, and your layout to cut.
What is a board foot?: It is the North American unit for pricing lumber: one board foot is a nominal 1 in × 12 in × 12 in, so a 2×4 is 0.667 board feet per foot and a 2×6 is 1. It is calculated from nominal sizes, which is the trade convention and not a mistake — the actual volume of a 2×4 is about 0.44 board feet per foot, so the figure on this page is roughly 50% more than the wood, and it is also not a weight.
16 in or 24 in on center?: 16 in is the residential default and the spacing most tables assume; 24 in saves studs and is common on non-bearing walls and on walls with thick enough sheathing to span it. The rule of thumb is that a bearing wall carrying a floor above stays at 16 in unless a span table says otherwise for your stud size. On the page the choice is a field, so you can price both: on a 40 ft wall the difference is ten studs.
How much top plate do I need?: Three runs of the wall length: one sole plate and a doubled top plate, which is the usual build for a bearing wall and what the plate figure reports. A partition wall that carries nothing above it is normally built with two runs, so multiply the plate linear feet by two thirds. The plate is reported separately from the studs because it is a different length — it runs with the wall, not up it — and it is the same lumber.
Does the wall height change the stud count?: No, and that catches people out. Height is eight feet in most houses and the studs are bought at that length, so it changes the stud linear feet and the board feet but not the number of pieces — a taller wall takes the same studs, each one longer. What does change the count is spacing and openings. If you are framing a wall over 10 ft, the studs become a special order and the price per piece steps up.

References

Lumber — nominal and actual dimensions, and the board-foot convention used to price framing lumber — Wikipedia
Approximate Conversions from U.S. Customary Measures to Metric — the feet, inches and millimetre spacings compared on this page — National Institute of Standards and Technology

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