Deck Calculator
Calculate the number of deck boards, total area, and linear footage for your deck project.
Common Deck Board Sizes
| Nominal Size | Actual Width | Actual Thickness | Notes |
|---|---|---|---|
| 5/4×6 | 5.5 in | 1.0 in | Most popular composite & PT decking |
| 2×6 | 5.5 in | 1.5 in | Solid, heavy; good for high-traffic |
| 2×4 | 3.5 in | 1.5 in | Narrower; more boards needed |
| 1×4 (hardwood) | 3.5 in | 0.75 in | Ipe, cedar, and tropical hardwoods |
Frequently Asked Questions
What is the actual width of a deck board?
Lumber is sold by nominal size, but the actual dimensions are smaller. Common deck board sizes: 2×6 has an actual width of 5.5 inches; 5/4×6 (the most popular decking) is also 5.5 inches actual; 2×4 is 3.5 inches actual. Always use actual dimensions, not nominal, when calculating board count.
What gap should I leave between deck boards?
The standard gap between deck boards is ¼ inch (0.25 in). This allows for water drainage and slight wood expansion. Pressure-treated lumber is often installed green (wet) and will shrink as it dries — some builders install wet PT boards with no gap, knowing they will shrink to ¼ inch. Composite decking manufacturers specify gaps in their installation guides.
How much extra decking should I order?
Add 10% for waste and end cuts on a straight-lay deck. Add 15% for diagonal installation. Waste comes from cuts at the rim joist, end trim, and any damaged or defective boards. Always check lumber at the yard and reject warped, cracked, or heavily knotted boards.
What is the maximum span for deck joists?
Joist spacing and span depend on lumber size and wood species. Common spans for Southern Yellow Pine: 2×8 joists at 16 in on center can span up to 12 feet; 2×10 can span 15 feet. Local building codes and the AWC Span Calculator should be consulted for structural design — this calculator covers decking boards only.
How do I calculate a diagonal deck layout?
For a diagonal 45° deck, boards run corner to corner. The effective span (and thus board count) increases by a factor of √2 (about 1.41). Calculate as you would for a straight deck, then multiply board count by 1.41, and add 15% waste factor. The boards will be longer and require more end cuts.