Lumber & Board Feet
Board feet, stud and joist counts, linear feet and total cost — with the nominal-versus-actual size trap handled properly.
Use the nominal size — the name on the label, like 2×6 — not the dressed size you measure with a tape. Board feet are priced on the nominal figure by long-standing convention.
Board feet
Nominal versus actual — dressed softwood
| Called | Actually measures | Millimetres | Board feet per 8 ft |
|---|
Members needed
| Spacing | Members | Sheathing joins land on a stud? |
|---|
Your cut list
Add every different size you need. The totals underneath add up board feet, linear feet and cost across the whole job.
Whole job
| Size | Length | Qty | Board ft | Linear ft | Cost |
|---|
How to use this calculator
Step by step
- On Board feet, enter the nominal size — 2×6, not the 1½×5½ you would measure — with the length in feet and the number of pieces. That is the convention lumber is priced on.
- The actual dressed size row shows what the board really measures, in inches and millimetres, so you can check clearances and joinery against reality.
- On Framing, give the wall length or joist span, the spacing on centre, and the length of each member. Corners and openings are added on top of the base count.
- The comparison table shows how the member count changes at 12, 16, 19.2 and 24 inch spacing — useful when weighing material cost against stiffness.
- On Cut list, add one line per size you need. The totals cover the whole job in board feet, linear feet and money.
- Add ten percent to whatever you calculate before ordering. Some boards will be crowned, split or twisted and get culled on site.
Good to know
- Board foot = nominal thickness × nominal width × length in feet, all divided by 12. One board foot is a piece 1 inch thick, 12 inches wide and a foot long.
- Nominal sizes are historical: a 2×4 was a rough-sawn 2 by 4 before it was planed. Everything sold today is dressed smaller, and there is no way to opt out.
- Spacing at 19.2 inches on centre exists because five bays make exactly 8 feet — a whole sheet of plywood with no offcut. It is a genuine standard, not a typo.
- Hardwood is sold by the board foot, softwood framing usually by the piece. Both are quoted on nominal dimensions.
- Order longer boards and cut them down where you can. Two 8-foot pieces from one 16-foot board is usually cheaper than buying the 8-footers separately.
- Kiln-dried softwood runs about 30 lb per cubic foot. Green lumber can be half again as heavy — worth knowing before you load a trailer.
The maths behind it
- Board feet BF = (T × W × L) ÷ 12 T and W in nominal inches, L in feet.
- Board feet from inches BF = (T × W × L) ÷ 144 When the length is in inches instead.
- Stud count n = ⌈length in inches ÷ spacing⌉ + 1 The +1 is the stud at the far end.
- Corner allowance +2 studs per corner A standard three-stud corner.
- Opening allowance +5 studs per opening Two kings, two trimmers, and cripples.
- Plate material run × (1 + number of top plates) Bottom plate plus single or double top.
- Dressed size under 2″: −¼″; 2″: −½″; width 8″+: −¾″ The standard surfacing losses for softwood.
Why does a 2×4 measure 1½ by 3½?
Because the nominal name describes the rough-sawn size before the board was planed smooth on all four faces. Surfacing removes about a quarter inch per face, and the naming stuck. Board feet are still calculated on the nominal figure — that is the trade convention, and it is what the yard charges on. Use the actual size for anything you are physically fitting.
Should I use 16 or 24 inch spacing?
Sixteen for load-bearing walls and anywhere you want a stiff wall for drywall or tile. Twenty-four is permitted for many non-bearing and single-storey applications and uses noticeably less material, but the wall flexes more and drywall can telegraph the studs. Check your local code before deciding — it is not purely a preference.
Does the framing count include plates and headers?
Plates are worked out separately and reported in linear feet, since they come from long stock rather than stud-length pieces. Headers are not included, because their size depends entirely on the span and load above the opening — that needs a span table, not a multiplier.
How much waste should I allow?
Ten percent for straightforward work, fifteen to twenty for anything with lots of angles or short pieces, where offcuts pile up fast. On a cut list of mostly long straight runs you can go lower, but never to zero — some boards are simply unusable.
Is a board foot the same as a linear foot?
No. A linear foot just measures length, ignoring the cross-section. A board foot measures volume. Twelve linear feet of 1×12 is twelve board feet; twelve linear feet of 1×4 is only four. Both figures are reported here because suppliers quote sometimes one and sometimes the other.