How to Calculate Board Feet: Lumber Buying Guide

Understanding board feet is the difference between buying exactly what you need and wasting hundreds on unnecessary lumber. This guide explains the formula, decodes nominal vs actual dimensions, and shows you how to calculate material costs for any project.

The Quick Answer

For a deck project requiring 10 pieces of 2×6×8 boards:

• Board feet per piece: 8 board feet
• Total board feet: 80 BF
• Estimated cost: $240-$320 (at $3-$4 per board foot)

One 2×6×8 board contains 8 board feet because: (2” × 6” × 8’) ÷ 12 = 8 BF. When shopping, multiply total board feet by your local price per board foot to estimate costs before checkout.

The Board Foot Formula

A board foot is a volume measurement: one square foot of wood that’s one inch thick. Think of it as a 12” × 12” × 1” piece of lumber.

$\text{Board Feet} = \frac{\text{Thickness (in)} \times \text{Width (in)} \times \text{Length (ft)}}{12}$

Why divide by 12? Because thickness and width are measured in inches, but length is measured in feet. Dividing by 12 converts everything to a consistent cubic volume measurement.

Example Calculation

For a 2×6 board that’s 10 feet long:

1. Thickness: 2 inches
2. Width: 6 inches
3. Length: 10 feet
4. Calculation: (2 × 6 × 10) ÷ 12 = 120 ÷ 12 = 10 board feet

Important: Use the nominal dimensions (2×6), not actual dimensions (1.5” × 5.5”), for board foot calculations. The lumber industry standardized board feet based on the advertised nominal size, even though the actual milled lumber is smaller.

Nominal vs Actual Lumber Dimensions

This is where beginners get confused. A 2×4 board is not 2 inches by 4 inches. When lumber is first cut at the sawmill, it starts at the nominal (named) size. Then it’s dried and planed smooth, which removes about 1/2 inch from each face.

Complete Size Chart

1-by Lumber (1x boards)

Nominal Size	Actual Size	Common Uses
1×2	3/4” × 1-1/2”	Trim, lattice, furring strips
1×3	3/4” × 2-1/2”	Trim, shelving, paneling
1×4	3/4” × 3-1/2”	Trim, siding, tongue-and-groove
1×6	3/4” × 5-1/2”	Shelving, fence boards, siding
1×8	3/4” × 7-1/4”	Shelving, shiplap, wide trim
1×10	3/4” × 9-1/4”	Shelving, stair treads
1×12	3/4” × 11-1/4”	Shelving, wide boards, workbenches

2-by Lumber (2x boards - Dimensional Framing)

Nominal Size	Actual Size	Common Uses
2×2	1-1/2” × 1-1/2”	Stakes, light framing
2×4	1-1/2” × 3-1/2”	Wall framing, studs (most common)
2×6	1-1/2” × 5-1/2”	Joists, rafters, deck boards
2×8	1-1/2” × 7-1/4”	Floor joists, beams, headers
2×10	1-1/2” × 9-1/4”	Floor joists, beams, long spans
2×12	1-1/2” × 11-1/4”	Stairs, large beams, deck joists

4-by Lumber (4x boards - Heavy Framing)

Nominal Size	Actual Size	Common Uses
4×4	3-1/2” × 3-1/2”	Deck posts, pergola supports
4×6	3-1/2” × 5-1/2”	Large posts, heavy beams
4×8	3-1/2” × 7-1/4”	Structural beams, large headers
4×10	3-1/2” × 9-1/4”	Heavy beams, bridge supports
4×12	3-1/2” × 11-1/4”	Large structural beams

6-by and Larger (Timber)

Nominal Size	Actual Size	Common Uses
6×6	5-1/2” × 5-1/2”	Large posts, structural timber
6×8	5-1/2” × 7-1/4”	Heavy beams, structural supports
8×8	7-1/4” × 7-1/4”	Timber framing, large posts

Why the difference? When rough-sawn lumber dries, it shrinks. Then planing (smoothing) the surface removes another 1/4” to 1/2” from each face. The lumber industry kept the traditional nominal names for marketing consistency, even though actual dimensions are smaller.

Common Lumber Sizes and When to Use Each

Understanding which board to choose saves money and prevents structural issues.

Framing Lumber (2x boards)

2×4 boards are the workhorse of construction:

• Wall studs (16” or 24” on center)
• Interior partition walls
• Light framing and blocking
• Temporary bracing

2×6 boards provide more strength:

• Exterior wall framing (better insulation space)
• Floor joists for short spans (under 10 feet)
• Deck boards and deck framing
• Rafters for moderate roof slopes

2×8, 2×10, 2×12 boards for structural loads:

• Floor joists for longer spans
• Headers over windows and doors
• Deck beams and rim joists
• Stair stringers

Finish Lumber (1x boards)

1×4 and 1×6 boards for trim and paneling:

• Baseboards and crown molding
• Window and door trim
• Fence pickets
• Shiplap or tongue-and-groove walls

1×8, 1×10, 1×12 boards for wider applications:

• Shelving
• Wide trim boards
• Stair treads
• Furniture building

Posts and Beams (4x and larger)

4×4 posts for vertical support:

• Deck posts
• Pergola columns
• Mailbox posts
• Short fence posts

6×6 and larger for heavy-duty:

• Timber frame construction
• Large deck posts spanning multiple stories
• Structural beams for open floor plans

Lumber Grades: Select, Construction, Utility

Not all lumber is created equal. Grades determine strength, appearance, and price.

Grading System

Appearance Grades (for visible wood):

• Select or Clear: Minimal knots, smooth grain, best appearance. Use for trim, furniture, cabinets. Costs 2-3× more than construction grade.
• No. 1 Common: Small knots and minor imperfections. Good for painted projects.
• No. 2 Common: Larger knots and blemishes. Acceptable for rustic looks or non-visible areas.

Structural Grades (for framing):

• Stud Grade: Standard 2×4 wall studs. Meets code for load-bearing walls.
• No. 1 & Better: Higher strength for joists and rafters. Fewer defects.
• No. 2: Most common framing lumber. Adequate strength for typical residential construction.
• Utility: Lowest grade. Use only for blocking, bracing, or non-structural applications.

How to Read Grade Stamps

Every piece of dimensional lumber has a stamp showing:

• Species: SPF (Spruce-Pine-Fir), SYP (Southern Yellow Pine), HEM-FIR (Hemlock-Fir)
• Grade: Stud, #2, #1, etc.
• Moisture content: S-DRY (surface dry, under 19%), KD (kiln-dried)
• Mill identification

Example stamp: “HEM-FIR | S-DRY | STUD” means hemlock-fir, surface-dried, stud grade suitable for wall framing.

Linear Feet vs Board Feet: When Each Matters

Linear feet measures length only. Board feet measures volume (length × width × thickness). Use the right measurement for each situation.

When to Use Linear Feet

• Fencing: 100 feet of fence needs 100 linear feet of rail boards, regardless of board size
• Deck railings: Measured by perimeter distance
• Trim molding: Priced per linear foot because all trim is the same thickness
• Rope, wire, pipe: One-dimensional materials

Example: You need 50 linear feet of 1×6 fence boards. Buy 50 feet of 1×6 lumber, which equals 25 board feet (0.5 BF per linear foot for 1×6).

When to Use Board Feet

• Lumber pricing: Most dimensional lumber is priced per board foot
• Project estimating: Calculate total wood volume needed
• Hardwood purchasing: Hardwood is almost always sold by the board foot
• Comparing different sizes: Which is cheaper, 10 2×6×8 boards or 8 2×8×8 boards?

Example: A deck requires 200 board feet of 2×6 decking. Calculate linear feet needed: 200 BF ÷ 0.5 BF per linear foot = 400 linear feet. For 12-foot boards, that’s 34 boards.

How Lumber is Priced

Understanding pricing structures prevents overpaying.

Pricing Methods

Per Board Foot (most common for dimensional lumber):

• Typical range: $1.50 - $6.00 per board foot depending on species, grade, and market
• Softwood framing: $2.50 - $4.00 per BF (as of 2026)
• Hardwood: $4.00 - $15.00+ per BF depending on species
• Formula: Total cost = Board feet × Price per BF

Per Piece (big box stores):

• Convenient but hides the per-BF cost
• Compare prices by calculating BF and dividing by piece price
• Example: $8.50 for a 2×6×8 (8 BF) = $1.06 per BF (excellent price)

Per MBF (thousand board feet - wholesale):

• Lumberyards selling in bulk
• Example: $2,400 per MBF = $2.40 per board foot
• Formula: Price per BF = MBF price ÷ 1,000

Price Comparison Example

Which is the better deal?

• Option A: 2×6×10 boards at $12.50 each
• Option B: 2×6×8 boards at $9.00 each

Calculate board feet per piece:

• Option A: (2 × 6 × 10) ÷ 12 = 10 BF per board
• Option B: (2 × 6 × 8) ÷ 12 = 8 BF per board

Calculate price per board foot:

• Option A: $12.50 ÷ 10 BF = $1.25 per BF
• Option B: $9.00 ÷ 8 BF = $1.13 per BF

Winner: Option B is 10% cheaper per board foot. If you can work with 8-foot boards, buy those and save.

Standard Lumber Lengths

Dimensional lumber comes in 2-foot increments. Knowing available lengths helps minimize waste.

Common Lengths Available

Length	Uses	Availability
6 feet	Short projects, blocking	Limited in big box stores
8 feet	Most common framing length	Widely stocked
10 feet	Longer walls, joists	Widely stocked
12 feet	Joists, long spans, deck boards	Widely stocked
14 feet	Large rooms, commercial	Special order
16 feet	Floor joists, deck beams	Special order
18-20 feet	Commercial framing	Lumberyard only

Stocking tip: Big box stores (Home Depot, Lowe’s) stock 8’, 10’, and 12’ lengths regularly. Longer lengths require special order or a lumber supply yard.

Calculating Waste and Cutoffs

The 10% waste rule: Always add 10% to your lumber order to account for:

• Damaged or warped boards you reject
• Cutting mistakes
• Unusable cutoff pieces
• Last-minute design changes

Example: Your deck needs 180 board feet of 2×6. Order 180 × 1.10 = 198 board feet (round up to 200 BF).

Calculating for Specific Projects

Real-world examples show how to apply the board foot formula to common builds.

Example 1: Deck Project

Project: 12’ × 16’ deck with 2×6 boards laid perpendicular to joists 16” on center.

Step 1: Calculate deck area

• 12’ × 16’ = 192 square feet

Step 2: Account for board coverage

• 2×6 boards have 5-1/2” actual width
• With 1/8” gap between boards: 5-5/8” total per board
• Coverage per linear foot: 5.625” ÷ 12” = 0.469 square feet per linear foot

Step 3: Calculate linear feet needed

• 192 sq ft ÷ 0.469 = 409 linear feet

Step 4: Convert to board feet

• 2×6 lumber: 1 linear foot = 1 board foot
• Total: 409 board feet

Step 5: Determine number of boards

• Using 12-foot boards: 409 ÷ 12 = 34.1 → 35 boards
• Board feet check: 35 boards × 12 BF per board = 420 BF (includes waste)

Step 6: Calculate cost

• At $3.50 per board foot: 420 BF × $3.50 = $1,470

Example 2: Framing a Room

Project: Frame a 10’ × 12’ room with 8-foot ceilings.

Materials needed:

• Wall studs (2×4×8):

  • Perimeter: (10’ + 12’) × 2 = 44 feet
  • Studs at 16” on center: 44 ÷ 1.33 = 33 studs
  • Top/bottom plates: 44 feet × 2 = 88 linear feet = 12 boards
  • Total 2×4×8: 45 boards
  • Board feet: 45 × 5.33 BF = 240 BF

• Door header (2×8×10):

  • 1 board = 13.33 BF

Total board feet: 253 BF Cost at $2.80/BF: $708

Example 3: Fence Calculation

Project: 100-foot fence with 6-foot tall 1×6 boards.

Picket boards:

• Boards per foot: 12” ÷ 5.5” actual width = 2.18 boards per foot
• Total boards: 100 feet × 2.18 = 218 boards
• Using 6-foot 1×6: 218 boards
• Board feet per 6-foot 1×6: (1 × 6 × 6) ÷ 12 = 3 BF
• Total: 218 × 3 = 654 board feet

Rails (2×4×8):

• 3 rails per section: top, middle, bottom
• 100 feet ÷ 8-foot sections = 13 sections
• Rails needed: 13 × 3 = 39 boards
• Board feet: 39 × 5.33 = 208 BF

Posts (4×4×8):

• Posts every 8 feet: 13 posts
• Board feet: 13 × 10.67 = 139 BF

Total fence: 1,001 board feet Cost at $3.00/BF: $3,003

Pro Tips for Buying Lumber

1. Bring a Tape Measure and Check Every Board

Don’t assume lumber is straight. Sight down the length and check for:

• Bow: Curve along the face
• Twist: Board spirals along its length
• Cup: Curve across the width
• Checks: Cracks perpendicular to grain

Reject any board with more than 1/4” deviation over 8 feet. Warped lumber wastes time and money trying to force it straight.

2. Buy Longer Boards to Minimize Joints

Fewer joints = stronger structure and faster installation. If your deck is 14 feet long, buy 16-foot boards instead of joining two 8-footers. Yes, longer boards cost slightly more per board foot, but you save on labor and fasteners.

3. Shop Local Lumberyards for Better Quality

Big box stores prioritize price over quality. Local lumberyards often stock:

• Higher grades (fewer knots and defects)
• Better moisture content (properly kiln-dried)
• More species options (cedar, redwood, hardwoods)
• Knowledgeable staff who can recommend the right material

Expect to pay 10-20% more, but you’ll get straighter, stronger lumber.

4. Understand Moisture Content

Green lumber (fresh-cut, high moisture) is cheaper but shrinks as it dries, causing:

• Warping and twisting
• Gaps opening between boards
• Nail pops and cracks

Kiln-dried (KD) lumber has moisture reduced to 15-19% and is dimensionally stable. Look for the “KD” stamp. Always use KD lumber for interior projects and visible surfaces.

5. Calculate Board Feet Before You Shop

Walk into the store knowing exactly how many board feet you need. This prevents:

• Overbuying and wasting money
• Underbuying and making extra trips
• Sales pressure to buy unnecessary extras

Use the formula: (Thickness × Width × Length) ÷ 12 = Board feet

6. Time Your Purchase

Lumber prices fluctuate with housing market demand. Buy during:

• Winter months (November-February): Lowest demand, best prices
• Midweek (Tuesday-Thursday): Less crowded, better selection

Avoid buying during:

• Spring and summer (April-August): Peak building season, highest prices
• Weekends: Picked-over inventory

Frequently Asked Questions

How do I calculate board feet for odd-sized lumber?

Use the same formula: (Thickness × Width × Length in feet) ÷ 12. For example, a 1×7 board that’s 9 feet long: (1 × 7 × 9) ÷ 12 = 5.25 board feet. The formula works for any dimensions, even non-standard sizes like 1×7 or 5×5.

Do I use nominal or actual dimensions for board feet calculations?

Always use nominal dimensions (the advertised size like 2×4) for board foot calculations, not actual dimensions (1.5” × 3.5”). The lumber industry standardized board feet based on nominal sizes, so all pricing and estimating uses nominal measurements.

What’s the board foot measurement for plywood?

Plywood is sold by the sheet (4’ × 8’ = 32 square feet), not by board feet. A 3/4” thick sheet of plywood contains 2 board feet (0.75” ÷ 12 × 32 sq ft), but retailers don’t price it that way. Calculate plywood needs by sheet count, not board feet.

How many 2×4 studs do I need per linear foot of wall?

For standard framing with studs 16 inches on center: 0.75 studs per linear foot of wall. A 10-foot wall needs 7-8 studs. For 24” on center spacing: 0.5 studs per linear foot. Always add extra for corners, door frames, and window openings.

Can I convert board feet to cubic feet?

Yes: 1 board foot = 1/12 cubic foot (144 cubic inches). To convert board feet to cubic feet, divide by 12. For example, 60 board feet = 5 cubic feet. This matters when calculating truck bed capacity or storage space.

Why is lumber priced higher in some regions?

Regional pricing depends on:

• Distance from sawmills: West Coast states near forests pay less
• Transportation costs: Remote areas pay shipping premiums
• Local building codes: Hurricane or earthquake zones require higher-grade lumber
• Supply and demand: High-growth areas have higher prices

Expect 30-50% price variation between regions. West Coast lumber averages $2.50/BF while Northeast markets can hit $4.50/BF for the same material.

Ready to calculate your project? Use our lumber calculator to get instant board foot estimates and cost breakdowns for any build.