Lumber Calculator
Timber is priced by board foot in North America and by cubic metre or linear metre in the UK. This calculator converts between them and works out how many lengths a job needs.
Formula
Usable cuts per board = board length ÷ (cut length + kerf)
- Kerf is the width the blade removes, typically 3 mm or 1/8 inch
- Board feet = thickness (in) × width (in) × length (ft) ÷ 12
A 2.4 m board cut into 600 mm pieces with a 3 mm kerf: 3 pieces, 183 mm spare
Board Feet
A board foot is 144 cubic inches: nominally one foot square and one inch thick.
Board feet = (thickness in × width in × length in) ÷ 144
A 2×4 at 8 feet measures 1.5″ × 3.5″ × 96″ = 504 in³, which is 3.5 board feet.
Note the actual dimensions. A "2 by 4" is 1.5 by 3.5 inches once planed, and pricing usually uses those nominal names while the timber is smaller.
Cutting and Waste
Add 10–15% for offcuts, and more where the design produces awkward lengths. Every cut also removes the saw kerf, typically 3 mm, which matters when several pieces come from one length.
Cutting four 600 mm pieces from a 2.4 m length looks exact and is not: three kerfs consume around 9 mm, so the last piece falls short. Plan cutting lists against real board lengths rather than dividing totals.
Moisture and Movement
Timber moves with humidity, expanding across the grain and barely at all along it. Kiln-dried stock at 8–12% moisture is stable indoors; green or damp timber will shrink noticeably as it dries, opening joints and cupping boards.
Let new timber acclimatise in the room where it will live for a week or two before cutting, and design joints so seasonal movement is accommodated rather than fought.
Quick Reference
| Cut length | Pieces | Used | Offcut |
|---|---|---|---|
| 300 mm | 7 | 2,121 mm | 279 mm |
| 400 mm | 5 | 2,015 mm | 385 mm |
| 600 mm | 3 | 1,809 mm | 591 mm |
| 800 mm | 2 | 1,606 mm | 794 mm |
| 1,200 mm | 1 | 1,203 mm | 1,197 mm |
Frequently Asked Questions
- What is a board foot?
- 144 cubic inches of timber, nominally a foot square and an inch thick. Multiply thickness by width by length in inches and divide by 144.
- Why is a 2x4 not actually 2 by 4 inches?
- The nominal size refers to rough-sawn dimensions before planing. A finished 2×4 measures about 1.5 by 3.5 inches.
- How much waste should I allow?
- Between 10 and 15 per cent, more for complex cutting lists. Remember the saw kerf removes about 3 mm at every cut.
- Does timber shrink after I buy it?
- It moves with humidity, mostly across the grain. Let it acclimatise indoors for a week or two before cutting, and buy kiln-dried stock for interior work.