★ CONSTRUCTION · DECKS · LUMBER
26 boards, 416 linear feet, $1,040.00. A 12 ft wide deck in 5/4×6 boards needs 26 boards at 16 ft long, and the last board needs 2.25 inches trimmed off it. Enter your deck size and board to size your deck and your cost.
A deck board is sold by its nominal size and milled smaller: a 5/4×6 board is really 5.50 inches wide. This calculator works out the boards, the linear feet and the cost for any deck from the board’s real face width, with the full nominal-to-actual size table and the gap between boards.
A deck board is sized from its face width, and the face width is not the number on the label. Lumber is sold by its nominal size and milled smaller: a 5/4×6 board is really 5.50 inches across the face, a 1×4 is 3.50 inches, a 2×8 is 7.25 inches and a 2×12 is 11.25 inches. Each board covers its face width plus the gap between boards, which is 1/8 inch by default. The boards needed are the deck width in inches divided by the coverage per board, rounded up — the last board is trimmed to fit, so the count always rounds up, never down. The linear feet are the boards times the board length, and the cost is the linear feet times the price per linear foot. The actual coverage is the boards times the coverage, which is always a little more than the deck width — the difference is what you trim off the last board.
At the default — a 12 ft wide deck, 16 ft boards, 5/4×6 boards at $2.50 a linear foot, gap 1/8 in — the face width is 5.50 in and the coverage per board is 5.50 + 0.125 = 5.625 in. The deck is 12 × 12 = 144 in wide, so the boards are 144 ÷ 5.625 = 25.6, rounded up to 26 boards. The linear feet are 26 × 16 = 416 ft and the cost is 416 × $2.50 = $1,040.00. The actual coverage is 26 × 5.625 = 146.25 in (12.19 ft), which is 2.25 in more than the deck — that is what you trim off the last board.
| Nominal size | Actual face width (in) | Coverage with 1/8 in gap (in) |
|---|---|---|
| 1×4 | 3.50 | 3.625 |
| 1×6 | 5.50 | 5.625 |
| 5/4×6 | 5.50 | 5.625 |
| 2×4 | 3.50 | 3.625 |
| 2×6 | 5.50 | 5.625 |
| 2×8 | 7.25 | 7.375 |
| 2×10 | 9.25 | 9.375 |
| 2×12 | 11.25 | 11.375 |
| Case | Boards | Linear ft | Cost |
|---|---|---|---|
| Default (12 ft wide, 16 ft long, 5/4×6, $2.50/ft) | 26 | 416 | $1,040.00 |
| 1×4 boards | 40 | 640 | $1,600.00 |
| 1×6 boards | 26 | 416 | $1,040.00 |
| 2×8 boards | 20 | 320 | $800.00 |
| 2×10 boards | 16 | 256 | $640.00 |
| 2×12 boards | 13 | 208 | $520.00 |
| 10 ft wide deck | 22 | 352 | $880.00 |
| 20 ft wide deck | 43 | 688 | $1,720.00 |
| 8 ft wide deck | 18 | 288 | $720.00 |
| 16 ft wide deck | 35 | 560 | $1,400.00 |
| 20 ft long boards | 26 | 520 | $1,300.00 |
| 12 ft long boards | 26 | 312 | $780.00 |
| 10 ft long boards | 26 | 260 | $650.00 |
| $3.50/lin ft | 26 | 416 | $1,456.00 |
| $1.75/lin ft | 26 | 416 | $728.00 |
| Gap 0 in | 27 | 432 | $1,080.00 |
Setup: deck width 12 ft, board length 16 ft, board size 5/4×6, price $2.50 a linear foot, gap 1/8 in.
Line 1 — the face width. A 5/4×6 board is really 5.50 in wide, not 6 in.
Line 2 — the coverage per board. 5.50 + 0.125 = 5.625 in.
Line 3 — the deck width in inches. 12 × 12 = 144 in.
Line 4 — the boards. 144 ÷ 5.625 = 25.6, rounded up to 26 boards.
Line 5 — the linear feet. 26 × 16 = 416 ft.
Line 6 — the cost. 416 × $2.50 = $1,040.00.
Line 7 — the actual coverage. 26 × 5.625 = 146.25 in (12.19 ft).
Line 8 — the trim. 146.25 − 144 = 2.25 in to trim off the last board.
Reverse: a 2×6 on a 12 ft deck needs 26 boards; 20 boards of 5/4×6 cover 112.50 in (9.38 ft); 30 boards at 16 ft are 480 linear ft; 416 ft at $3.00 a foot is $1,248.00; a 2×12 on a 16 ft wide deck needs 17 boards; a 1×4 on a 20 ft wide deck needs 67 boards.
1×4 boards: the face is 3.50 in and the coverage is 3.625 in, so 144 ÷ 3.625 = 39.72, rounded up to 40 boards. 640 ft, $1,600.00 — narrow boards cost more, because there are more of them.
1×6 boards: the face is 5.50 in, the same as a 5/4×6, so the count is the same: 26 boards, 416 ft, $1,040.00. A 1×6 and a 5/4×6 cover the same width; the difference is the thickness.
2×8 boards: the face is 7.25 in and the coverage is 7.375 in, so 144 ÷ 7.375 = 19.53, rounded up to 20 boards. 320 ft, $800.00.
2×10 boards: the face is 9.25 in and the coverage is 9.375 in, so 144 ÷ 9.375 = 15.36, rounded up to 16 boards. 256 ft, $640.00.
2×12 boards: the face is 11.25 in and the coverage is 11.375 in, so 144 ÷ 11.375 = 12.66, rounded up to 13 boards. 208 ft, $520.00 — the cheapest case on the page, because wide boards mean fewer boards.
10 ft wide deck: 120 ÷ 5.625 = 21.33, rounded up to 22 boards. 352 ft, $880.00.
20 ft wide deck: 240 ÷ 5.625 = 42.67, rounded up to 43 boards. 688 ft, $1,720.00.
8 ft wide deck: 96 ÷ 5.625 = 17.07, rounded up to 18 boards. 288 ft, $720.00.
16 ft wide deck: 192 ÷ 5.625 = 34.13, rounded up to 35 boards. 560 ft, $1,400.00.
20 ft long boards: the count stays 26 boards, but the linear feet are 26 × 20 = 520 ft and the cost is $1,300.00. Longer boards cost more per board, not more boards.
12 ft long boards: 26 boards, 312 ft, $780.00.
10 ft long boards: 26 boards, 260 ft, $650.00.
$3.50/lin ft: the count stays 26 boards and 416 ft, but the cost is 416 × $3.50 = $1,456.00.
$1.75/lin ft: 26 boards, 416 ft, $728.00.
Gap 0 in: the coverage is 5.50 in with no gap, so 144 ÷ 5.50 = 26.18, rounded up to 27 boards. 432 ft, $1,080.00. No gap wastes width — but boards swell with moisture, so a zero gap is not recommended.
Reverse — the other way round: a 2×6 on a 12 ft deck needs 26 boards; 20 boards of 5/4×6 cover 112.50 in (9.38 ft); 30 boards at 16 ft are 480 linear ft; 416 ft at $3.00 a foot is $1,248.00; a 2×12 on a 16 ft wide deck needs 17 boards; a 1×4 on a 20 ft wide deck needs 67 boards.
The model assumes the deck width, board length, board size, price and gap you enter, the table’s nominal-to-actual sizes, and a 1/8 in gap by default. It assumes the boards run across the width you enter and the board length is the deck’s other dimension, with no waste for cuts, no butt joints and no picture-frame border. Widths that are not whole feet use the next row up in board count, because the count always rounds up. It leaves out framing, fasteners, railing, stairs and waste — the $1,040.00 at the defaults is the decking boards only, not the deck. Rounding convention: board counts and linear feet are whole numbers rounded up, coverage is shown to three decimals, money is rounded to cents, and all figures are computed from unrounded values, rounded only for display.
| Output | Formula | What it means |
|---|---|---|
| Board face width | nominal size → milled size | 5.50 in for a 5/4×6. |
| Coverage per board | face width + gap | 5.625 in. |
| Boards needed | ceil(deck width in inches ÷ coverage) | 26 boards. |
| Linear feet | boards × board length | 416 ft. |
| Cost | linear feet × price per linear foot | $1,040.00. |
| Actual coverage | boards × coverage | 146.25 in (12.19 ft). |
| To trim | actual coverage − deck width | 2.25 in off the last board. |
| Boards for a 2×6 on a 12 ft deck | ceil(144 ÷ 5.625) | 26 boards. |
| Max deck width for 20 boards | 20 × coverage | 112.50 in (9.38 ft). |
| Linear feet for 30 boards × 16 ft | 30 × 16 | 480 ft. |
| Cost for 416 ft at $3.00/lin ft | 416 × $3.00 | $1,248.00. |
| Boards for a 2×12 on a 16 ft deck | ceil(192 ÷ 11.375) | 17 boards. |
| Boards for a 1×4 on a 20 ft deck | ceil(240 ÷ 3.625) | 67 boards. |
| 1×4 boards | same model, 1×4 | Face 3.50 in, coverage 3.625 in, 40 boards, 640 ft, $1,600.00. |
| 1×6 boards | same model, 1×6 | Face 5.50 in, coverage 5.625 in, 26 boards, 416 ft, $1,040.00. |
| 2×8 boards | same model, 2×8 | Face 7.25 in, coverage 7.375 in, 20 boards, 320 ft, $800.00. |
| 2×10 boards | same model, 2×10 | Face 9.25 in, coverage 9.375 in, 16 boards, 256 ft, $640.00. |
| 2×12 boards | same model, 2×12 | Face 11.25 in, coverage 11.375 in, 13 boards, 208 ft, $520.00. |
| 10 ft wide deck | same model, 10 ft wide | Face 5.50 in, coverage 5.625 in, 22 boards, 352 ft, $880.00. |
| 20 ft wide deck | same model, 20 ft wide | Face 5.50 in, coverage 5.625 in, 43 boards, 688 ft, $1,720.00. |
| 8 ft wide deck | same model, 8 ft wide | Face 5.50 in, coverage 5.625 in, 18 boards, 288 ft, $720.00. |
| 16 ft wide deck | same model, 16 ft wide | Face 5.50 in, coverage 5.625 in, 35 boards, 560 ft, $1,400.00. |
| 20 ft long boards | same model, 20 ft long | Face 5.50 in, coverage 5.625 in, 26 boards, 520 ft, $1,300.00. |
| 12 ft long boards | same model, 12 ft long | Face 5.50 in, coverage 5.625 in, 26 boards, 312 ft, $780.00. |
| 10 ft long boards | same model, 10 ft long | Face 5.50 in, coverage 5.625 in, 26 boards, 260 ft, $650.00. |
| $3.50/lin ft | same model, $3.50 a foot | Face 5.50 in, coverage 5.625 in, 26 boards, 416 ft, $1,456.00. |
| $1.75/lin ft | same model, $1.75 a foot | Face 5.50 in, coverage 5.625 in, 26 boards, 416 ft, $728.00. |
| Gap 0 in | same model, no gap | Face 5.50 in, coverage 5.500 in, 27 boards, 432 ft, $1,080.00. |
The math is exact for the numbers you enter: the coverage is the face width plus the gap, the boards are the deck width divided by the coverage rounded up, and the cost is the boards times the length times the price. What the model cannot do is see your boards: check the actual face width, because real boards vary a little and a board that is a sixteenth narrower changes the count on a wide deck. It assumes no waste, no butt joints and no border, and leaves out framing, fasteners, railing and stairs. For the cost of the whole deck, see deck cost calculator; for the board feet behind it, see board foot calculator.
Bright Side Kit. "Deck Board Size Chart: Width, Spacing & Board Count." https://brightoolbox.com/deck-board-size-chart/ Accessed October 25, 2026.26 boards for a 12 ft wide deck in 5/4×6. A 5/4×6 board is really 5.50 inches wide, and with a 1/8 in gap each board covers 5.625 inches. The deck is 12 ft wide, which is 144 inches, and 144 ÷ 5.625 = 25.6, rounded up to 26 boards — the last board is trimmed, so the count always rounds up. At 16 ft long that is 416 linear feet, which is $1,040.00 at $2.50 a foot.
Because lumber is sold by its nominal size and milled smaller. A 5/4×6 board is 5.50 inches across the face, a 1×4 is 3.50 inches, a 2×8 is 7.25 inches and a 2×12 is 11.25 inches. The board count has to use the actual face width, not the nominal size — counting a 5/4×6 as 6 inches wide would leave you two boards short on a 12 ft deck.
1/8 inch (0.125 in) is the default here, and it is the usual spacing for wood decking. The gap lets water drain and gives the boards room to swell when they get wet. A zero gap needs 27 boards instead of 26 on a 12 ft deck — one more board, $40.00 more — and it is not recommended, because boards swell with moisture and a deck with no gaps holds water.
Boards times board length times the price per linear foot. At the defaults that is 26 boards × 16 ft = 416 linear feet, and 416 × $2.50 = $1,040.00. At $3.50 a foot the same deck is $1,456.00; at $1.75 a foot it is $728.00. The cost here is the boards only — framing, fasteners and railing are separate.
13 boards for a 12 ft wide deck, or 17 for a 16 ft wide deck. A 2×12 board is really 11.25 inches wide, and with a 1/8 in gap each board covers 11.375 inches. On a 12 ft deck that is 144 ÷ 11.375 = 12.66, rounded up to 13 boards. On a 16 ft deck it is 192 ÷ 11.375 = 16.88, rounded up to 17 boards.
67 boards. A 1×4 board is really 3.50 inches wide, and with a 1/8 in gap each board covers 3.625 inches. A 20 ft deck is 240 inches wide, and 240 ÷ 3.625 = 66.21, rounded up to 67 boards. Narrow boards always need more of them — a 1×4 deck needs two and a half times as many boards as a 5/4×6 deck the same size.
112.50 inches, which is 9.38 ft. Each board covers 5.625 inches, so 20 boards cover 20 × 5.625 = 112.50 inches. That is the widest deck 20 boards will cover without trimming the last board down to nothing — a 10 ft deck needs 22 boards, not 20.