Lumber Calculator
Works out how many stock lengths of lumber to buy for a run of cut pieces, and shows the offcut each board leaves so you can pick the length that wastes least.
Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
The formula
cut pieces = ceiling(total run ÷ piece length × (1 + waste)) stock lengths = ceiling(cut pieces ÷ floor(stock ÷ piece))
Both roundings go upward because you cannot buy part of a board or use an offcut shorter than a piece. The second floor is where waste hides: a 4.8 m board yields two 2.4 m pieces exactly, but only one 2.5 m piece, with 2.3 m left over.
What to watch out for
The stock length decides the waste more than anything else:
- Pick a stock length the piece divides into. 2.4 m pieces from 4.8 m stock waste nothing; from 5.4 m stock they waste 600 mm every board.
- Longer stock is not always better. It costs more per metre, it is harder to handle, and it bows more in the rack.
- Sort on site. Framing lumber is graded, but the straightest boards still go where it matters — plates and the studs beside openings.
Frequently Asked Questions
How much lumber do I need?
Divide the total run by the cut length and add 10% for waste, then work out how many cut pieces come from each stock length. 60 m of 2.4 m pieces needs 28 pieces, which is 14 lengths of 4.8 m stock.
What lengths does lumber come in?
Metric stock runs 2.4, 3.0, 3.6, 4.2, 4.8 and 5.4 m. In the US it is 8, 10, 12, 14 and 16 ft. Pick the one your cut length divides into with least left over.
How much waste should I allow for framing lumber?
10% for ordinary framing. 15% where the stock is rough, reclaimed or has to be sorted for straightness, and less if every piece is a clean multiple of the stock length.