Dimensional lumber is quoted three different ways depending on who you ask: by the piece, by the linear foot, and by the board foot. This calculator converts between all three so you can compare quotes that are not stated in the same unit.
Buying hardwood by the board foot? See the Board Foot Calculator.
About pricing on this page
This calculator is intentionally price-light. Absolute dollar figures are deliberately omitted because they vary too widely by region, brand, and installer to be useful as planning estimates. The relative-comparison tables below show how options stack up against each other — which is the durable, actionable information. For a real budget, get two or three written quotes from local suppliers and contractors after they have seen the job.
Lumber Quantity and Cost Calculator
Choose a lumber size, enter quantity and length, and compare cost per piece, per linear foot, and per board foot.
Nominal vs Actual Lumber Dimensions
A 2 × 4 has not measured 2 by 4 inches since surfacing became standard. The nominal name refers to the rough sawn size before drying and planing.
| Nominal | Actual | BF per LF | BF in 8 ft | BF in 16 ft | Common Use |
|---|---|---|---|---|---|
| 1 × 4 | 3/4 × 3-1/2 in | 0.333 | 2.67 | 5.33 | Trim, furring, battens |
| 1 × 6 | 3/4 × 5-1/2 in | 0.500 | 4.00 | 8.00 | Fence boards, trim, shelving |
| 1 × 8 | 3/4 × 7-1/4 in | 0.667 | 5.33 | 10.67 | Shelving, fascia |
| 2 × 4 | 1-1/2 × 3-1/2 in | 0.667 | 5.33 | 10.67 | Wall framing, blocking |
| 2 × 6 | 1-1/2 × 5-1/2 in | 1.000 | 8.00 | 16.00 | Walls, rafters, decking |
| 2 × 8 | 1-1/2 × 7-1/4 in | 1.333 | 10.67 | 21.33 | Floor joists, headers |
| 2 × 10 | 1-1/2 × 9-1/4 in | 1.667 | 13.33 | 26.67 | Joists, beams, stringers |
| 2 × 12 | 1-1/2 × 11-1/4 in | 2.000 | 16.00 | 32.00 | Long joists, stair stringers |
| 4 × 4 | 3-1/2 × 3-1/2 in | 1.333 | 10.67 | 21.33 | Posts, fence posts |
| 6 × 6 | 5-1/2 × 5-1/2 in | 3.000 | 24.00 | 48.00 | Structural posts, timbers |
Board footage is conventionally calculated on nominal dimensions even though the actual size is smaller. A 2 × 4 counts as 0.667 board feet per linear foot despite measuring 1.5 by 3.5 inches.
Common Framing Lumber Applications
| Application | Typical Size | Spacing | Notes |
|---|---|---|---|
| Interior wall framing | 2 × 4 | 16 in OC | Precut 92-5/8 in studs for 8 ft walls |
| Exterior wall framing | 2 × 6 | 16 or 24 in OC | Deeper cavity for insulation |
| Floor joists (short span) | 2 × 8 | 16 in OC | Spans to about 12 ft |
| Floor joists (medium span) | 2 × 10 | 16 in OC | Spans to about 15 ft |
| Floor joists (long span) | 2 × 12 | 16 in OC | Spans to about 18 ft |
| Deck joists | 2 × 8 or 2 × 10 | 16 in OC | Pressure treated required |
| Roof rafters | 2 × 6 to 2 × 12 | 16 or 24 in OC | Size per span and snow load |
| Deck posts | 4 × 4 or 6 × 6 | Per plan | 6 × 6 for decks over 6 ft high |
| Fence posts | 4 × 4 | 6–8 ft OC | Pressure treated, ground contact rated |
| Stair stringers | 2 × 12 | 12–16 in OC | Cut depth reduces effective strength |
Lumber Price Multipliers by Grade and Treatment
Relative to standard kiln-dried SPF at the same dimension and length.
| Type | Price Multiplier | Use |
|---|---|---|
| Standard kiln-dried SPF | 1.0× | Interior framing, general use |
| Stud grade | 0.9× | Wall studs only, non-structural spans |
| Select structural | 1.25× | Longer spans, engineered loads |
| Pressure treated (above ground) | 1.35× | Decks, exterior framing |
| Pressure treated (ground contact) | 1.5× | Posts, sill plates, ground use |
| Douglas fir | 1.3× | Higher strength framing, West Coast |
| Cedar | 2.1× | Fencing, trim, exposed exterior |
| Redwood | 2.4× | Premium exterior, decking |
Pressure treated lumber arrives wet and shrinks as it dries, so deck boards installed tight will open up within a few months. Account for this when spacing deck boards.
Common Lumber Buying Mistakes
Comparing Prices in Different Units
A quote of $6.50 per piece, $0.81 per linear foot, and $1.22 per board foot can all describe the same 8-foot 2 × 4. Without converting to a common unit you cannot tell which supplier is cheaper. Convert everything to price per linear foot, which is the easiest unit to reason about for dimensional lumber.
Assuming Nominal Equals Actual
Designing a cavity for a 2 × 4 that is actually 1.5 by 3.5 inches matters when you are sizing insulation, planning a rough opening, or fitting trim. The half-inch difference per dimension compounds across an assembly, and it is why R-19 batts do not fit 2 × 4 walls despite both being described with the number four.
Buying Untreated Lumber for Ground Contact
Above-ground treated lumber and ground-contact treated lumber carry different chemical retention levels, and the distinction is not cosmetic. Above-ground material used as a buried post or a sill plate on concrete will fail within a few years. Check the end tag for the retention rating rather than assuming any green lumber will do.
Skipping the Waste Allowance on Framing
Ten percent is the practical floor on a framing order. It covers crooked pieces you set aside, cut-offs too short to use, and the occasional miscut. Lumber is also graded loosely enough that a bundle typically contains a few pieces too bowed or twisted to use for anything structural. Ordering exact count means a return trip.