Deck Board Calculator
Find out how many deck boards you need: enter your deck dimensions, board width and the gap between boards, and get the board count plus total linear feet — assuming full-length boards.
Result
| Exact boards | |
| Total linear length |
Units & conversions used
Imperial inputs are feet for deck dimensions and inches for board width and gap; results are board counts and linear feet/meters (1 ft = 0.3048 m). Metric inputs are converted first: 1 m = 3.28084 ft, 1 cm = 0.3937 in.
Formula & source
linear feet = boards × board length(ft)
Source: basic division — boards laid side by side across the deck width, each occupying its width plus one gap; no authority needed. Assumes full-length boards: every board spans the full deck length with no butt joints. Result is rounded up because you buy whole boards.
Worked example (you can verify by hand)
Input: 12×16 ft deck (boards run the 12-ft direction), 5.5 in boards, 0.25 in gap.
- Deck width in inches: 16 × 12 = 192 in
- Space per board: 5.5 + 0.25 = 5.75 in
- Exact boards: 192 ÷ 5.75 = 33.39 → 34 boards
- Linear feet: 34 × 12 = 408 ft (124.36 m)
Expected output: 34 boards, each 12 ft long — 408 linear ft total.
Limitations — what this cannot do
- Counts surface boards only. Joists, beams, posts, footings, ledger boards, screws/clips and flashing are not included — those need a separate framing plan.
- Assumes every board spans the full deck length. If your boards are shorter than the deck, butt joints and extra waste change the count — buy a few extra boards.
- Does not account for picture-frame borders, stair treads, or angled/herringbone patterns, all of which use more material.
- Actual board lengths sold vary (8, 12, 16, 20 ft); match your purchase to available lengths to minimize waste.
FAQ
Why do I need a gap between deck boards?
The gap lets rain drain through, allows the wood or composite to expand and contract with temperature and moisture, and keeps debris from trapping moisture between boards. 1/4 in is the typical spacing.
Does this include the deck frame?
No — this calculator counts surface boards only. The frame (joists, beams, posts) is a separate structural calculation that depends on spans, loads and local code.
What if my deck is longer than the boards I can buy?
Then boards must be joined end to end with butt joints, ideally staggered over joists. The calculator assumes full-length boards, so add a few extra boards for the joints and the offcuts they create.
Should I add extra boards for waste?
The count already rounds up to whole boards, which covers the fractional remainder. For complex shapes, stairs or a picture-frame border, buy 5–10% extra as a planning margin.
How many deck boards do I need?
Use the calculator at the top of this page: enter your deck's length and width, the actual board width (5.5 in for a nominal "6-inch" board), and the gap spacing (typically 1/4 in). It divides the deck width by (board width + gap) and rounds up to whole boards. Remember this counts surface boards only — the frame, stairs and fasteners are separate.
Concrete vs wood deck — which should I choose?
Wood/composite deck: faster and often cheaper to build, comfortable underfoot, but needs periodic sealing or staining (wood) and board replacement over a 15–25 year life. Concrete patio/slab: very low maintenance and a 30+ year life, but harder underfoot, slower to install (curing time), and harder to change later. For ground-level outdoor space a concrete slab is usually the economical choice; for an elevated structure attached to the house, a wood or composite deck is the practical one. Use our concrete slab calculator to compare material quantities.