Deck Board Calculator — Estimate Decking Materials
Enter your deck dimensions, board width, gap spacing, board length, and waste factor to instantly calculate the number of boards across, total linear feet needed, and how many boards to purchase. Supports 2×6, 2×4, composite, and custom board widths.
Deck Board Calculator
Estimate boards, linear feet, and board count for any deck size
Default: 1/8" (0.125)
Recommended: 10% for simple decks, 15% for diagonal patterns
Frequently Asked Questions
How do I calculate how many deck boards I need?
Divide your deck width (in feet) by the effective board width (board width + gap, converted to feet) to get boards across. Multiply by deck length to get linear feet. Add your waste factor (typically 10%), then divide by board length to get the total board count to purchase.
How many 2x6 boards do I need for a 12x16 deck?
A 2×6 board has an actual width of 5.5 inches. With a 1/8-inch gap (0.125"), the effective width is 5.625 inches = 0.469 feet. Boards across = ceil(12 / 0.469) = 26. Linear feet = 26 × 16 = 416 lf. With 10% waste = 457.6 lf. Using 8-foot boards: ceil(457.6 / 8) = 58 boards.
What is the standard gap between deck boards?
The standard gap for pressure-treated lumber installed wet is 1/8 inch (0.125"). As the boards dry, they shrink to approximately 1/4-inch gaps. For kiln-dried or composite lumber, install at 1/4 inch. Always check manufacturer specifications for composite decking, as hidden fastener clips have a built-in gap.
What waste factor should I use for decking?
Use 10% for a simple rectangular deck with boards running parallel. Use 15% for a 45-degree diagonal pattern. Use 15–20% for herringbone or picture-frame borders. For irregular L-shape decks, 10–12% is appropriate. It's always better to buy a little extra than to run short mid-project.
What is the actual width of a 2x6 deck board?
A nominal 2×6 board has an actual width of 5.5 inches (139.7 mm). The actual thickness is 1.5 inches. Lumber is sold by nominal size, but all calculations should use the actual (dressed) dimensions. Similarly, a 2×4 has an actual width of 3.5 inches, and a 2×8 measures 7.25 inches wide.
How many linear feet of decking do I need for a 200 sq ft deck?
For a 200 sq ft deck with 2×6 boards (5.5" wide) and 1/8" gap: effective board width = 0.469 ft. Linear feet = (deck width / 0.469) × deck length. For a 10×20 deck: boards across = ceil(10/0.469) = 22, linear feet = 22 × 20 = 440 lf. With 10% waste = 484 lf. Divide by your board length to get count.
Can I use this calculator for composite decking?
Yes. Enter the actual face width of your composite board in the board width field. For hidden fastener systems (Trex, TimberTech, Fiberon), use the gap specified by the manufacturer — typically 3/16 inch or the gap built into the fastener clip. Add at least 10% waste to account for end cuts.
What board length should I choose to minimize waste?
Choose a board length that divides evenly into your deck length, or is slightly longer. For a 16-foot deck, 16-foot boards have zero end waste — one board per run. For a 14-foot deck, 16-foot boards waste 2 feet each; 8-foot boards require two pieces (2 ft of waste on one). Compare total waste across options using the calculator.
Deck Board Calculator: Formula, Board Sizes & Gap Guide
This deck board calculator estimates the number of decking boards you need based on your deck dimensions, board width, gap spacing, and a waste factor. It outputs deck area, boards across, total linear feet, and the final board count to purchase.
Deck Board Formula
Boards Across the Deck
The number of boards laid perpendicular to the deck length:
Board width and gap are in inches, converted to feet by dividing by 12.
Linear Feet Required
Boards to Purchase
Effective board width = (5.5 + 0.125) / 12 = 0.469 ft
Boards across = ⌈12 / 0.469⌉ = 26
Linear feet = 26 × 16 = 416 lf
With 10% waste = 457.6 lf
Board count = ⌈457.6 / 8⌉ = 58 boards
Common Deck Board Sizes
Lumber is sold by nominal size, but the actual dimensions are smaller after milling. Use the actual width when calculating:
| Nominal Size | Actual Width | Notes |
|---|---|---|
| 2×4 | 3.5 inches | Narrow boards, more gaps, lighter look |
| 2×6 | 5.5 inches | Most common; good balance of strength and appearance |
| 5/4×6 (Radius Edge) | 5.5 inches | Thinner profile (1"), rounded edges, popular composite |
| 2×8 | 7.25 inches | Wider boards, fewer seams, premium look |
| Composite 1×6 | 5.5 inches | Trex, TimberTech — often includes hidden fastener gap |
Gap Spacing Guide
Gaps between deck boards allow for drainage, airflow, and wood expansion. The right gap depends on material and climate:
| Gap Size | Use Case |
|---|---|
| 1/8" (0.125") | Standard for pressure-treated and cedar when installed wet — boards shrink to ~1/4" gap as they dry |
| 1/4" (0.25") | Dry or kiln-dried lumber; hot, dry climates |
| 3/16" (0.1875") | Composite decking with face screws |
| Hidden fastener spec | Composite with hidden clips — gap built into clip (~3/16" to 1/4") |
Joist Spacing & Board Orientation
Joist spacing determines the required board thickness. Standard guidelines for pressure-treated lumber:
- 16" o.c. joists — 5/4×6 or 2×6 boards run perpendicular
- 24" o.c. joists — 2×6 minimum; 2×8 preferred for stiffness
- Diagonal pattern — reduce joist spacing by 25% (e.g., 16" → 12") or use thicker boards
- Herringbone / parquet — requires blocking between joists; add 15–20% waste factor
Waste Factor Recommendations
| Pattern / Situation | Recommended Waste % |
|---|---|
| Simple rectangle, parallel boards | 10% |
| L-shape or irregular deck | 10–12% |
| Diagonal (45°) pattern | 15% |
| Herringbone / picture frame | 15–20% |
| Multiple angles / curves | 20%+ |
Related Tools
- Board Feet Calculator — calculate lumber volume in board feet for purchasing and pricing.
- Concrete Calculator — estimate concrete volume for deck footings and piers.
- Stair Calculator — calculate rise, run, and stringer length for deck stairs.