About This Calculator
This calculator helps you estimate the number of timber members needed for framing walls, floors, or decks. You can enter an explicit count or provide an area with spacing to auto-calculate.
Results include linear metres, cubic metres, and board feet to suit both metric and imperial ordering systems.
Common Spacings
| Application | Spacing |
|---|---|
| Stud walls | 400 mm (16") or 600 mm (24") |
| Floor joists | 400 mm (16") typical |
| Roof rafters | 400-600 mm (16-24") |
| Decking joists | 400 mm (16") |
Tips
- • Add 10% wastage for cuts, defects, and waste
- • Check standard stock lengths to minimise offcuts
- • Board feet (BF) = thickness (in) × width (in) × length (ft) / 12
Ready to Calculate?
Enter member count or area with spacing to get quantities.
Open CalculatorRelated Calculators
CACalifornia Building Code (Title 24)
References & Sources
Standards Cited
- NDS — National Design Specification for Wood Construction
Standard for structural wood design in North America - PS 20 — American Softwood Lumber Standard (ALSC)
Defines nominal and actual dimensions for dimension lumber
Formulas Used
- Member count (area-based):
count = ceil(perpendicularSpan / spacing) + 1
Source: NDS — Perpendicular span = area / member length; +1 for the end member - Total linear length:
totalLength = memberCount × memberLength
Source: Basic geometry - Volume:
volume = totalLength × crossSectionWidth × crossSectionDepth
Source: Basic geometry - Board feet:
BF = actualWidth_in × actualDepth_in × length_ft / 12
Source: PS 20 / ALSC — Board foot is the standard NA unit for lumber volume (1 BF = 144 cubic inches)
Key Assumptions
- Lumber sizes use actual (dressed) dimensions: 2×4 = 1.5" × 3.5" (38 × 89 mm) — PS 20
- Standard lumber lengths: 8 ft, 10 ft, 12 ft, 14 ft, 16 ft — Industry standard