Lumber Calculator
Estimate the framing lumber for walls, a floor or a gable roof. You get studs and plates, joists and rim board, rafters and ridge, plus sheathing, total board feet and cost at your yard’s prices.
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Framing is counted piece by piece. Walls take about one stud per foot at 16 in on center plus three plates per foot of wall. Floors take length (in) ÷ spacing + 1 joists. Gable roofs take length (in) ÷ spacing + 1 rafters per side. Sheathing is area ÷ 32 sheets. A 40 ft run of 8 ft wall comes to 48 studs, 8 plates and 11 sheets, about 365 board feet of lumber.
How to use this lumber calculator
- Pick walls, floor or roof. Run each part of the building separately and add the lists together.
- Enter the dimensions and spacing. The calculator counts the pieces. Member sizes (header, joist and rafter depth) come from your plans or code span tables.
- Enter your prices per board foot and per sheet so the total matches your lumber yard.
- Read the order list, then use the detailed calculators below for cut lengths and angles.
Nominal and actual lumber sizes
| Nominal | Actual (in) | Board feet per ft | Typical use |
|---|---|---|---|
| 2×4 | 1½ × 3½ | 0.67 | Wall studs and plates |
| 2×6 | 1½ × 5½ | 1.00 | Exterior walls, rafters, deck joists |
| 2×8 | 1½ × 7¼ | 1.33 | Rafters, floor and deck joists |
| 2×10 | 1½ × 9¼ | 1.67 | Floor joists, headers, ridge boards |
| 2×12 | 1½ × 11¼ | 2.00 | Long joists, stair stringers |
| 4×4 | 3½ × 3½ | 1.33 | Fence and light deck posts |
| 6×6 | 5½ × 5½ | 3.00 | Deck and pergola posts |
Lumber comes in even lengths from 8 to 20 ft (some yards stock 22 and 24 ft). Studs also come precut: 92⅝ in for 8 ft walls, 104⅝ in for 9 ft and 116⅝ in for 10 ft.
Framing rules of thumb
- WallsAbout 1 stud per linear foot at 16 in on center. Plates are 3 × wall length (one bottom, two top).
- FloorsJoists = length (in) ÷ spacing + 1. Rim board runs along both long sides. One hanger per hung joist end.
- RoofsRafters per side = length (in) ÷ spacing + 1. The ridge board is usually one size deeper than the rafters.
- SheathingArea ÷ 32 for 4×8 sheets. Roofs use the sloped area, which is footprint plus overhang times the pitch factor.
- WasteAdd about 10% to every count for culls, cuts and mistakes.
Treated or untreated lumber
Use pressure-treated lumber wherever wood touches concrete or masonry (sill plates, bottom plates on a slab) and for outdoor work. Use ground-contact rated lumber for posts and anything buried or close to the soil. Treated lumber needs hot-dip galvanized or stainless fasteners and hardware. Indoors and above ground, standard kiln-dried framing lumber is fine.
Worked example: a 12 × 24 ft floor and walls
- Floor: 24 ft long, 12 ft joists at 16 in
- 19 joists (2×10 × 12 ft) + 4 rim boards
- Subfloor (288 sq ft + 10%)
- 10 sheets of 23/32 in T&G
- Walls: 72 ft perimeter, 8 ft high, 4 corners
- 70 studs + 15 plates
- Wall sheathing (72 × 8 + 10%)
- 20 sheets of 4×8
All 5 framing & lumber calculators
Detailed calculators for each part of a framing job: cut lengths, angles and exact counts.
Frequently asked questions
How do I estimate lumber for framing?
Count each part: about 1 stud per foot of wall plus 3 plates per foot, joists = length ÷ spacing + 1, rafters = length ÷ spacing + 1 per side, sheathing = area ÷ 32. Add 10%.
What are standard lumber lengths?
Even lengths from 8 to 20 ft, sometimes 22–24 ft. Precut studs are 92⅝, 104⅝ and 116⅝ in.
Why is a 2×4 not 2 inches by 4 inches?
2×4 is the nominal size before drying and planing. It actually measures 1½ × 3½ in, but board feet and prices use the nominal size.
How much does framing lumber cost?
Prices change often and vary by region, so enter your yard’s prices. The calculator totals board feet and sheets for you.
When do I need pressure-treated lumber?
Where wood touches concrete or masonry and outdoors. Use ground-contact lumber for posts and anything near the soil.
How much extra lumber should I order?
About 10% for cuts, culls and mistakes, and more for complex roofs.
What this calculator assumes
- Rectangular walls, floors and gable roofs at the spacing you choose. Waste is added to studs and sheets.
- Wall header stock is assumed to be doubled 2×10, 3 in longer than each opening. Ridge boards are one size deeper than the rafters.
- The calculator counts pieces but does not size members. Use your plans, local span tables or a design professional for joists, rafters, beams and headers.
- Prices are your entries and exclude tax and delivery.