Dimensional lumber is named by its nominal rough-sawn size – a 2×4 – but after drying and planing it is actually 1½ × 3½ in. Lumber yards sell construction lumber by the piece or the linear foot and hardwood by the board foot, and you will want the weight when loading a truck or a roof rack.
How to use the Lumber Calculator
- Nominal size
- Length
- Number of pieces
- Species
- Custom density
- Waste
- Price per piece
Results update as you type, and every field accepts the units shown in its menu.
How it works
Choose the nominal size, enter the length, the number of pieces, the species and the price per piece. The calculator works out the linear and board footage from nominal sizes, the actual volume and weight from the dressed sizes, and the cost after waste.
Nominal vs actual sizes
| Nominal | Actual (in) | Actual (mm) |
|---|---|---|
| 1×4 | 0.75 × 3.5 | 19 × 89 |
| 1×6 | 0.75 × 5.5 | 19 × 140 |
| 1×8 | 0.75 × 7.25 | 19 × 184 |
| 2×4 | 1.5 × 3.5 | 38 × 89 |
| 2×6 | 1.5 × 5.5 | 38 × 140 |
| 2×8 | 1.5 × 7.25 | 38 × 184 |
| 2×10 | 1.5 × 9.25 | 38 × 235 |
| 2×12 | 1.5 × 11.25 | 38 × 286 |
| 4×4 | 3.5 × 3.5 | 89 × 89 |
| 4×6 | 3.5 × 5.5 | 89 × 140 |
| 6×6 | 5.5 × 5.5 | 140 × 140 |
Tips for an accurate estimate
- Sketch the job and split irregular areas into rectangles, circles and triangles before you measure.
- Add a waste allowance – typically 5–10% for simple layouts and 15–20% for diagonal, curved or heavily cut work.
- Check the coverage or yield printed on the product, because sizes and densities vary between manufacturers.
- Buy all units of a finished material (tile, brick, siding) from the same batch so colours match, and keep a few spares for repairs.
- Confirm local prices – quarry, lumber and steel prices vary widely by region and season.
Common mistakes to avoid
- Ordering exactly the calculated amount with no allowance for breakage, offcuts and settlement.
- Forgetting to subtract doors, windows and other openings – or subtracting small ones that still need cutting around.
- Confusing US short tons (2,000 lb) with metric tonnes (1,000 kg) when comparing quotes.
Inputs explained
| Field | What to enter |
|---|---|
| Nominal size | Choose one: 1×4, 1×6, 1×8, 2×4 … |
| Length | Choose one: 6 ft, 8 ft, 10 ft, 12 ft … |
| Number of pieces | A number |
| Species | Choose one: Douglas fir, Southern yellow pine, Eastern white pine, Ponderosa pine … |
| Custom density | Units: kg/m³, lb/ft³, g/cm³, lb/yd³ |
| Waste | In % |
| Price per piece | Units: /piece |
What each result means
- Linear feet = [Number of pieces]×[Length]
- Board feet (nominal) = [Nominal thickness]×[Nominal width]×[Length]×[Number of pieces]
- Actual volume = [Actual thickness]×[Actual width]×[Length]×[Number of pieces]
- Pieces to buy (with waste) = ceil([Number of pieces]×(1 + [Waste]÷100))
- Cost = [Pieces to buy (with waste)]×[Price per piece]
Formula
Linear feet = pieces × lengthBoard feet = nominal thickness × nominal width × length (ft) ÷ 12 × piecesWeight = actual volume × wood densityWorked example
Inputs — Nominal size: 2×4; Length: 8 ft; Number of pieces: 20; Species: Spruce-pine-fir; Custom density: 450 kg/m³; Waste: 10 %; Price per piece: $4.5 /piece.
Results — Linear feet = 160 ft; Board feet (nominal) = 106.67 board ft; Actual volume = 5.83 ft³; Approximate weight = 153 lb; Pieces to buy (with waste) = 22; Cost = $99.00.
Frequently asked questions
What are the actual dimensions of a 2×4?
1½ × 3½ in (38 × 89 mm). 2×6 is 1½ × 5½, 2×8 is 1½ × 7¼, 2×10 is 1½ × 9¼ and 2×12 is 1½ × 11¼.
How much does a 2×4×8 weigh?
About 9–12 lb dry depending on species; pressure-treated lumber can weigh 50% more while it is still wet.
How many board feet are in a 2×4×8?
5.33 board feet using nominal sizes.
What formula does the Lumber Calculator use?
Linear feet = pieces × length.