Calculator 03 / Lumber & Framing
Lumber Calculator
A board foot is a volume, not a length — thickness × width × length — which is why two boards of the same length can price very differently. Get board footage for a lumber order, or stud count for framing a wall on 16" or 24" centers.
How this calculator works
Board footage uses nominal (not actual/dressed) dimensions, matching how lumber yards price and quote material. The stud formula gives a standard 16"/24" on-center layout plus common allowances for corners, wall intersections, and rough openings — always confirm against your actual framing plan.
Two worked examples
Board feet: ten 2×6×8 boards, 10% waste.
- Per board = (2 × 6 × 8) ÷ 12 = 8 board feet
- Ten boards = 80 board feet
- With 10% waste = 88 board feet
Studs: a 20 ft wall at 16" O.C., two corners, one door opening.
- Base run = (20 × 12) ÷ 16 = 15, plus one to close the end = 16 studs
- Corners = 2 × 2 = 4 studs
- Opening = 1 × 3 = 3 studs
- Total = 23 studs
The "plus one" is the stud that closes the last bay. Leave it out and every wall you frame comes up exactly one short, which is the most common arithmetic error in framing takeoffs.
Nominal versus actual size
A 2×4 has not measured two inches by four since kiln drying and surfacing became standard. You order, pay and calculate board feet in nominal sizes; you build to the actual ones. Both numbers matter, at different moments.
| Nominal | Actual (dressed) | Board feet per 8 ft |
|---|---|---|
| 1×4 | ¾ × 3½" | 2.67 |
| 1×6 | ¾ × 5½" | 4.00 |
| 2×4 | 1½ × 3½" | 5.33 |
| 2×6 | 1½ × 5½" | 8.00 |
| 2×8 | 1½ × 7¼" | 10.67 |
| 2×10 | 1½ × 9¼" | 13.33 |
| 2×12 | 1½ × 11¼" | 16.00 |
| 4×4 | 3½ × 3½" | 10.67 |
The pattern behind the actual column: nominal widths up to 6 inches lose half an inch, and anything over 6 inches loses three quarters. That is why a 2×8 is 7¼ and not 7½ — the single most misremembered dimension on a framing site.
Choosing on-center spacing
Spacing is a structural decision before it is a material one, and it has to come from your plans or your local code. What it does to the count is straightforward: dropping from 16 to 24 inches removes roughly a third of the studs in a run.
| Spacing | Studs in a 20 ft wall | Where it is used |
|---|---|---|
| 12" O.C. | 21 | Tall walls, heavy point loads |
| 16" O.C. | 16 | The residential default |
| 24" O.C. | 11 | Advanced framing, usually with 2×6 |
Twenty-four inch spacing only saves money if the rest of the assembly is designed for it — thicker studs, and joists and trusses stacked directly over each. Applied to a wall that was drawn for 16 inches, it is not an economy, it is a defect.
What the corner and opening allowances assume
The two extra studs per corner match a conventional three-stud corner, which gives you a nailing surface for drywall on the inside face. The three per opening covers two trimmers carrying the header plus one additional king stud beyond what the run already provides.
| Detail | Extra studs | Notes |
|---|---|---|
| Three-stud corner | +2 | What this calculator assumes |
| Two-stud corner with drywall clips | +1 | Saves lumber and allows more insulation |
| Wall intersection (tee) | +2 | Count it as a corner here |
| Door or window opening | +3 | Two trimmers plus a king |
| Cripples above and below | not counted | Add separately for tall openings |
Headers, plates and blocking are not in this count either. Plates alone are easy to forget and easy to work out: a wall needs one bottom plate and usually two top plates, so three times the wall length in linear feet.
Where lumber takeoffs go wrong
- Using actual dimensions for board feet. Board feet are always nominal. Calculating a 2×6 as 1½ × 5½ understates the order by about 31%.
- Dropping the closing stud. The base count is spacing plus one. Every wall, every time.
- Forgetting plates, headers and blocking. This tool counts studs. On a typical wall the plates add roughly three linear feet of material per foot of wall.
- Ordering the exact length you need. Framing lumber comes in even lengths. A 9 ft wall plate is cut from a 10 ft board, and the offcut is usually scrap.
- Ignoring grade and moisture. Board feet say nothing about whether the material is fit for the job. Green lumber shrinks as it dries, and a stud that was straight on delivery may not be a fortnight later.
Where these numbers come from
Nominal sizes, dressed sizes and panel span ratings are set by published standards rather than by convention. These are the bodies that set them.
- American Lumber Standard Committee — Administers PS 20, the American Softwood Lumber Standard — the source of every dressed dimension in the table above.
- APA – The Engineered Wood Association — Panel grades, thicknesses and span ratings for plywood and OSB sheathing.
- American Wood Council — Design values, span tables and the framing publications behind residential stud and joist layout.
Nominal vs. actual lumber size — which do I use?
Use nominal size (the size printed on the label, e.g. 2×6) for board footage — that's how lumber is bought and sold, even though the actual dressed size is smaller (a 2×6 is really 1.5"×5.5").
Should I round up individual board lengths?
Yes — lumber is sold in standard lengths (8', 10', 12', 16', etc.). Round each board up to the next stock length before ordering, even though this calculator computes raw board footage.
Can I save, share, or print a calculation?
Yes — use the Save, Copy link, and Print buttons under your results. Saved calculations can be grouped into a named project on the My Projects page for a combined job estimate with cost totals. Everything is stored only in your browser, never uploaded — see the Privacy Policy for details.
Estimates only. Confirm final counts against your framing plan and local building code requirements.