Why decking is counted in rows and bought in lineal feet
Decking is the one deck material that cannot be estimated from area alone. Two decks of exactly 200 sq ft take different amounts of board depending on how wide the boards are and how big a gap you hold, because the gap is area you pay nothing to cover. So the takeoff runs in three stages: how many rows fit across the width, how many lineal feet those rows total, and how many pieces of your stock length that is.
Start with the module — the board width plus the gap. A 5.5 in board with a 3/16 in gap has a 5.6875 in module. Divide the deck width by the module and round up, and you have the row count. There is one subtlety worth getting right: N rows contain only N − 1 gaps, because the far edge of the last board has no gap beyond it. That is why the formula adds one gap to the width before dividing. On a 144 in deck it makes the difference between 25.32 and 25.35 rows — both round to 26 — but on a deck whose width lands close to a whole module it changes the answer by a full row.
Then multiply the rows by the deck length to get bare lineal feet. That is the number you would need if every board came in exactly the right length and nothing was cut wrong. Add a waste allowance on top, and divide by the stock length to reach the board count.
One thing this arithmetic does not decide for you is which way the boards run. Deck boards must cross the joists at right angles or on the diagonal — never parallel to them — so the direction is fixed by the framing beneath. Enter the deck length as the dimension parallel to the boards.
Coverage, gaps and the waste allowance
The useful shortcut behind all of this is that lineal feet per 100 sq ft = 1,200 ÷ module. A 5.5 in board at a 3/16 in gap has a 5.6875 in module, so it takes 1,200 ÷ 5.6875 = 211 lineal ft to cover 100 sq ft. A 3.5 in board at the same gap needs 325 lineal ft for the same 100 sq ft — nearly 55% more board, more than 50% more fasteners, and considerably more labour. That is the real cost of narrow decking, and it is invisible if you estimate by area.
The gap deserves more thought than it usually gets. Wet pressure-treated southern yellow pine is normally laid tight, because it shrinks across its width as it dries and opens its own gap — often 1/4 in or more. Kiln-dried lumber and every composite board must be gapped at installation, because they will not shrink to make room. Composite manufacturers also specify an end gap that varies with the temperature at installation, since the material expands lengthwise with heat; that gap is set by the manufacturer's table, not by this calculator.
The waste allowance covers three separate things: offcuts left when a board length does not divide neatly into the deck length, boards rejected for crook, wane or a bad crown, and mistakes. Ten percent is the normal figure for a plain rectangle. Add to it for stairs, for a picture-frame border (which needs mitres and a doubled rim), for cut-outs around posts, and for any deck with more than four corners. A 45° diagonal layout adds another increment because every single board gets two angled end cuts instead of two square ones — the trade rule of thumb is 15% total rather than 10%. If you want to reason about waste more carefully across the whole job, the construction waste factor calculator does that generally.
Fasteners scale with rows and joists, not with area: each board crosses each joist once, and each crossing takes two face screws or one hidden clip. A 16 × 12 deck framed at 16 in on centre has 13 joists and 26 rows, so 338 crossings — 676 screws face-fastened. Screws are sold by count and by weight, so check the box quantity rather than assuming a pound covers a deck.
Worked example: a 16 ft × 12 ft deck in 5/4 × 6
You are decking a 16 ft by 12 ft rectangle with 5/4 × 6 pressure-treated boards, which measure 5.5 in wide. Joists run at 16 in on centre across the 12 ft dimension, so the boards run the 16 ft way. You will hold a 3/16 in gap, allow 10% waste, and buy 16 ft boards at $22 each, face-screwed.
- Module. 5.5 + 0.1875 = 5.6875 in.
- Deck width in inches. 12 × 12 = 144 in.
- Rows. (144 + 0.1875) ÷ 5.6875 = 25.35, rounded up to 26 rows.
- Check the coverage. 26 boards and 25 gaps span 26 × 5.5 + 25 × 0.1875 = 143 + 4.6875 = 147.69 in. That is 3.69 in more than the deck, so the last board gets ripped down or the extra is spread across the gaps. Twenty-five rows would span only 142.0 in and leave a 2 in strip uncovered.
- Bare lineal feet. 26 × 16 = 416 ft.
- With waste. 416 × 1.10 = 457.6 ft.
- Boards. 457.6 ÷ 16 = 28.6, so 29 boards of 16 ft.
- Joists crossed. 192 in ÷ 16 = 12 spaces, so 13 joists.
- Screws. 26 × 13 × 2 = 676.
- Cost. 29 × $22 = $638 for the decking.
Sense-check it against the shortcut: the deck is 192 sq ft, and at 211 lineal ft per 100 sq ft that is 405 ft before waste. The row-by-row figure of 416 ft is 2.7% higher, and it should be — the row method rounds up to a whole board across the width, and the shortcut does not.
How to read the result before you order
Look at the row overhang first. The calculator tells you how far past the deck width the last row lands. If it is a fraction of an inch, let it cantilever past the rim joist as a drip edge. If it is 3 or 4 in, you have a decision: rip the last board, which leaves a narrow strip that looks like an afterthought, or widen the gap by a hair across every row to absorb it. Spreading 3.69 in over 25 gaps adds 0.15 in per gap, taking a 3/16 in gap to 5/16 in — noticeable but uniform, and far better looking than a 1.8 in rip at the house wall. Whichever you choose, decide before you fasten the first board, and start from the house so the cut row lands at the outer edge where a fascia can cover it.
Then look at the stock-length table. Longer boards mean fewer butt joints, and every butt joint on a deck is a maintenance liability because water sits in it. But a 16 ft board on a 12 ft deck wastes 4 ft per row unless you can use the offcuts elsewhere. The rule that actually matters: pick the stock length that is a whole multiple of, or slightly longer than, your deck length. A 12 ft deck wants 12 ft boards; a 20 ft deck wants 20 ft boards or two 10 ft boards per row with staggered joints.
Check the span rating against the joist spacing. This is where people get hurt. Most 5/4 pressure-treated decking is rated for 16 in on centre. Most capped composite is rated 16 in on centre for a straight layout but only 12 in on centre for a 45° layout, because a diagonal board spans 1.41 times the joist spacing. Some composite stair treads require 12 in regardless. Look up your specific board — the joist span calculator handles the framing side of the same question.
Finally, sanity-check the cost per square foot. Divide the material cost by the deck area. If that number is far from what you expected, the usual cause is a narrow board: the same deck in 3.5 in stock needs 55% more lineal feet than in 5.5 in stock.
Lineal feet of decking per 100 square feet
| Actual board width | 1/8 in gap | 3/16 in gap | 1/4 in gap |
|---|---|---|---|
| 3.5 in (2x4) | 331.0 ft | 325.4 ft | 320.0 ft |
| 5.25 in | 223.3 ft | 220.7 ft | 218.2 ft |
| 5.5 in (5/4x6, 2x6) | 213.3 ft | 211.0 ft | 208.7 ft |
| 7.25 in (2x8) | 162.7 ft | 161.3 ft | 160.0 ft |
These are bare coverage figures with no waste allowance. A 192 sq ft deck in 5.5 in boards at a 3/16 in gap needs 1.92 × 211 = 405 lineal ft before waste.
Stagger the butt joints, and land them on a joist
Every butt joint must land on a joist, and every joint needs full bearing — which usually means the joist gets a sistered nailer or a doubled member so each board end has its own fasteners rather than sharing a 1.5 in face. Stagger joints so that no two adjacent rows break over the same joist; a three- or four-row repeat looks deliberate, while random joints look like a mistake.
If you can avoid joints entirely by buying full-length boards, do it. Joints are where water sits, where the board ends check, and where a deck starts to fail first.
Mistakes that blow the decking order
- Using nominal width. A 5/4x6 is 5.5 in, not 6 in. Using 6 in under-counts the rows by about 9%.
- Forgetting the gap in the row count. Twenty-six boards laid with 3/16 in gaps cover 4.7 in more than twenty-six boards laid tight.
- Estimating by area with no gap correction. Area alone ignores both the gap and the round-up on the last row.
- Ordering the wrong stock length. A 12 ft deck decked in 16 ft boards throws away a quarter of every board unless the offcuts serve the stairs or a landing.
- Assuming a diagonal layout is free. It adds waste, and it usually forces the joists closer together because the board spans 41% further between them.
- Ignoring end gaps on composite. Composite boards move lengthwise with temperature, and the required end gap depends on the temperature the day you install.
- Counting fasteners by area. Fasteners follow rows times joists. Halving the board width nearly doubles the screw count for the same deck.
The rest of the deck takeoff
Decking is one line on a deck estimate and rarely the largest. Beneath it, the joists, beam and ledger are sized by span — the floor joist span calculator settles the joist size and spacing, and the framing lumber is priced by the board foot with the board foot calculator. The posts land on footings that have to be sized for the soil, which is the deck footing size calculator.
Above the deck surface, any walking surface more than 30 in above grade needs a guard, and the guard needs infill that a 4 in sphere cannot pass — the baluster spacing calculator divides a rail evenly to that limit. Stairs off the deck start with the stair rise and run calculator, and the treads on those stairs come out of the same decking order, so add their lineal feet to the figure on this page before you buy.
The framing conventions used here follow the American Wood Council's Prescriptive Residential Wood Deck Construction Guide (DCA 6), which is the document most inspectors work from for residential decks built without an engineer's stamp. It sets joist spans, ledger fastening, post and beam sizes and guard details, but it does not set decking span — that comes from the board manufacturer's own listing or from the lumber grading rules.
Key terms
- Lineal foot
- One foot of board length, regardless of width. Decking is estimated in lineal feet and sold by the piece.
- Module
- The repeating dimension across a deck: board width plus gap. Row count is deck width divided by the module.
- 5/4 decking
- Nominal five-quarter stock, actually about 1 in thick and 5.5 in wide. Standard residential decking in pressure-treated softwood.
- Hidden fastener
- A clip or biscuit that fixes the board through its edge groove, leaving no screw heads on the surface. Usually one per board per joist.
- Picture frame
- A border board mitred around the perimeter of a deck. It adds waste and requires extra framing beneath the mitres.