Decking Calculator
Take off a deck surface: enter the deck dimensions, the board width including the gap you'll leave, the board length, joist spacing, and waste, and get boards, joists, and lineal footage — then print it as a material order sheet with a screw estimate. Coverage math with practice-figure defaults: the framing itself (beams, posts, footings) and the joist sizing are separate questions. Free, no login.
Deck
Materials
Boards by coverage; joists for the deck length at spacing. Planning figures — add beams, posts, and blocking separately.
Decking Calculator — Material Order Sheet
Prepared with NORDIX — nordixhq.com/tools/decking-calculator
| Deck: 16 × 12 ft (192 ft²) | Board: 5.5" × 16 ft | Joists: 16" o.c. | Waste: 10% |
| Item | Qty | Unit | Notes |
|---|---|---|---|
| Deck boards | 29 | pieces | 16 ft boards (464 lineal ft), waste included |
| Joists | 13 | pieces | 16" o.c. across the deck length |
| Deck screws | 629 | screws | 2 per board–joist crossing (estimate) |
Method: boards by coverage (board width incl. gap × length) with waste; joists across the deck length at spacing; fasteners at 2 per board–joist crossing. Empirical planning figures — beams, posts, blocking, hangers, and stairs excluded; confirm against the deck plan.
How this calculator works
Boards are counted by coverage — how much deck one board blankets, gap included — and joists by spacing along the deck length:
boards = ⌈area ÷ (width÷12 × length) × (1 + waste%)⌉ · joists = ⌊length ÷ spacing⌋ + 1
The board width you enter is the actual face width plus the gap, not the nominal size: a 5/4×6 measures about 5-1/2", so with a 1/8" gap enter roughly 5.6 — entering the nominal 6 undercounts boards by about 8%. Grooved composite with hidden fasteners typically lands at 5.7–5.75 once the clip gap is in. The waste default of 10% is a planning allowance for a rectangular deck run perpendicular to the joists; diagonal layouts, picture-frame borders, and cut-up shapes run 15% or more. Joist spacing is a practice figure with a real constraint behind it: 16" o.c. is standard for 5/4 wood run perpendicular, while diagonal decking and many composites need 12" o.c. per the manufacturer’s span rating.
Worked example
A 16 × 12 ft deck, 5.5" boards (gap included) 16 ft long, joists at 16" o.c., 10% waste:
- Area: 16 × 12 = 192 ft²; one board covers (5.5 ÷ 12) × 16 = 7.33 ft².
- Boards: 192 ÷ 7.33 × 1.10 = 28.8 → 29 boards (464 lineal ft).
- Joists: ⌊16 ÷ 1.333⌋ + 1 = 13 joists across the deck length.
- Screws (order sheet): 2 per board–joist crossing ≈ 629 screws — an estimate; hidden-fastener systems run about one clip per crossing instead.
Enter the same deck above (the calculator’s defaults) to reproduce it, then print the order sheet.
Reference: decking per 100 ft² by board width (practice figures)
Computed with the same coverage math, for 16-ft boards before waste. The entered width is always face width plus gap — which is why the composite row needs fewer boards than its nominal size suggests.
| Width incl. gap | Typical product | Boards / 100 ft² | Lineal ft / 100 ft² |
|---|---|---|---|
| 5.5" | 5/4×6 face width, boards tight (calculator default) | 14 | 218.2 |
| 5.6" | 5/4×6 wood incl. ⅛" gap | 14 | 214.3 |
| 5.75" | grooved composite incl. clip gap | 14 | 208.7 |
Frequently asked questions
How many deck boards do I need?
The calculator works by coverage: deck area divided by the coverage of one board (its width including the gap, times its length), increased by your waste percentage and rounded up to whole boards. A 16 × 12 ft deck (192 sq ft) with 5-1/2 in. boards 16 ft long and 10% waste comes to 29 boards. Ordering board lengths that match your joist layout with minimal splicing keeps the real count close to the math.
What board width should I enter?
The actual face width plus the gap you will leave between boards, in inches — not the nominal size. A 5/4x6 deck board actually measures about 5-1/2 in., so with a 1/8 in. gap enter roughly 5.6; grooved composite boards with hidden fasteners usually land around 5.7–5.75 once the clip gap is included. Entering the nominal 6 in. would undercount boards by roughly 8%.
What joist spacing should I use for a deck?
16 in. on center is the standard for 5/4 wood decking run perpendicular to the joists. Diagonal decking and many composite products need tighter framing — often 12 in. o.c. — so check the decking manufacturer's span rating before you set joist layout. The calculator counts joists along the deck length at whatever spacing you enter, plus one to close the run; verify the framing itself against the building code adopted in your jurisdiction.
How much waste should I add for decking?
10% is a reasonable default for a rectangular deck with boards run perpendicular to the joists — treat it as an estimating allowance, not a standard. Go to 15% or more for diagonal (45°) decking, picture-frame borders, or decks with angles and cutouts, since every mitered end throws off more scrap. Runs pieced from short stock also waste more than long single-board runs.
Does the calculator include beams, posts, and fasteners?
No — it returns deck boards and a joist count only; beams, posts, footings, rim joists, blocking, and hangers are separate takeoff lines. For fasteners, a common estimating rule of thumb is two screws at every board-joist crossing — roughly 350 screws per 100 sq ft at 16 in. o.c. — while hidden-fastener systems run about one clip per crossing. Ledger and structural connections are their own hardware list.
Method: boards by coverage (face width incl. gap × board length) with the entered waste — the waste percentage and the 2-screws-per-crossing fastener rule are planning figures, not standards; joists counted along the deck length at spacing, plus one to close the run. Excluded: beams, posts, footings, rim joists, blocking, hangers, ledger hardware, and stairs — separate takeoff lines. Joist size and allowable span come from the IRC deck provisions (R507) or an engineer, and composite spacing limits from the decking manufacturer — verify the framing against the code adopted in your jurisdiction.
Pair with the Joist Span Calculator for what governs the framing under the boards, the Board Foot Calculator to price the lumber list, or the Stud & Framing Calculator for the wall framing takeoff.