EstimatorKitFree deck materials list
Deck calculator — the whole materials list, not just the boards
Give the length along the house and the projection out from it, and this returns the order: decking boards in the stock length that wastes least, joists at the spacing your boards are rated for, beam plies, posts, footings, screws or hidden clips, joist hangers, ledger fasteners and balusters. Rows are counted as boards plus the gaps between them, because a 5 1/2 in board on a 1/4 in gap covers 5 3/4 in of run — which is also how the page can tell you what the last board rips to, and what gap would let every board land whole instead.
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- No signup
- Feet, inches and fractions
- Gap counted, not ignored
- Wood and composite spans
Radius-edge pressure-treated, 1 in thick when it is dressed. The default board on nine decks in ten, and the one that arrives wet.
Boards run the length, joists run the width. Both take a tape reading as written: 16' 4 1/2", 196.5 in and 5 m all parse.
Turning the boards 45 degrees lengthens the distance they reach between joists, so the frame tightens to 12 in (IRC Table R507.7 — 1 1/4 in nominal decking laid at 45 degrees).
Gap default is 1/8" — wet pressure-treated boards go down nearly tight because they shrink across the face as they dry. It moves with how long the stack sat at the yard; a soaking-wet 5 1/2 in board loses close to 1/4 in. Measure a board before you trust the face width: brands come in at 5.5, 5.4 and 5.36 in and the difference is a whole board across a wide deck.
Post spacing is what the beam span table decides, not this page — the beam size, the species and the joist span it carries set the maximum, and the table is in the same part of the code as the joist spans below.
Decking to order
28 boards × 16 ft
- Deck area
- 192 sq ft
- Bare, no allowance
- 416 linear ft
- With 5% for cuts
- 437 linear ft
- Rows across 12'
- 26
- Offcut at 16 ft
- 0 linear ft
- Butt joints, all over joists
- 0
The last board across
26 boards at 5 1/2" with 1/8" between them cover 12', which leaves the last one to rip to 3 3/8". Wide enough to fasten normally, though it is worth putting it against the house rather than at the outer edge where everyone stands.
Reset the gap to 9/32" and 25 full boards land flush with no rip at all. Nobody has ever noticed a thirty-second of an inch spread across two dozen joints; a ripped strip down one edge is the first thing anyone sees.
Dividing the 12' by the board face and ignoring the gaps would call for 27 boards. The gaps do 2.2% of the covering, so that count is 1 too many — bought, carried and stacked behind the shed.
| Length | How it cuts | Boards | Thrown away |
|---|---|---|---|
| 8 ft | 2 boards to reach across one row | 52 | 0 ft |
| 10 ft | 2 boards to reach across one row | 52 | 104 ft |
| 12 ft | 2 boards to reach across one row | 52 | 208 ft |
| 14 ft | 2 boards to reach across one row | 52 | 312 ft |
| 16 ft | 1 row out of each board | 26 | 0 ft |
The 16 ft board wastes least here. A row longer than one board has to be joined over a joist, and that joist wants doubling or a cleat behind it — this layout has none.
Frame
- Joists, 2 x 10 at 16 in
- 13 × 12 ft
- Ledger, 16 ft sticks
- 1
- Rim joist, 16 ft sticks
- 1
- Mid-span blocking
- 12 pieces, 14.5 ft
- Beam, 2-ply
- 2 boards of 16 ft
- Posts, 6 x 6
- 4 × 1' 4 1/2"
- Footings to dig
- 4
Post length is measured from the top of the footing to the underside of the beam, with the decking, the joist and the beam taken off the finished height. Footing diameter, depth and the concrete in them are a separate question — size them for your frost line and soil, then pour by the hole.
Checks against the published tables
A 2 x 10 of southern pine at 16 in centers is listed at 14'; this deck asks it to span 12'. Read off the deck joist span table in IRC R507, numbered R507.6 in the 2021 edition, at 40 psf live plus 10 psf dead, No. 2 grade, wet service. Reference, not approval — the grade stamp on the actual boards, the load you put on the deck and your building department all outrank a table on a web page.
Blocking is in the list because the joists run past 8 ft — IRC R502.7.1 calls for bridging at 8 ft intervals once a joist's depth-to-thickness ratio passes 6 to 1, which is every 2 x 10 and 2 x 12.
Hardware
- Deck screws
- 676 (2 boxes)
- Per square foot of deck
- 3.52
- Joist hangers
- 13
- Hanger nails, every hole
- 130
- Ledger fasteners at 15 in
- 14
- Post bases and post caps
- 4 each
Two screws per board per joist, plus two more at every butt joint because both board ends land on the same joist. A box holds about 350, the count in a 5 lb box of 2 1/2 in coated deck screws; that count moves with gauge, length and coating — five pounds of 3 in screws is nearer 260 of them. Ledger spacing is read off the deck ledger connection table by joist span; stagger the two rows and keep them off the ends.
Guard
- Railing to build
- 37 linear ft
- Sections between posts
- 7
- Guard posts, 4 x 4
- 9
- Top, bottom and cap rail
- 111 linear ft
- Balusters
- 84
- Clear gap that gives
- 3 7/8"
12 balusters in each 68 1/2" opening leave 3 7/8" of daylight, inside the 4 in the code allows (IRC R312.1.3 — no opening in a guard may pass a 4 in sphere). The count is driven up by the baluster face, not down: fatter balusters need more of them, not fewer, because the gap between them has to shrink to stay legal.
This deck stands 36 in above grade, past the 30 in that puts a guard on it, so the rail goes up 36 in — IRC R312.1.2 — a guard on a one- or two-family dwelling stands at least 36 in high.
Stairs are not in this list. The flight down to the yard has its own rise, run and stringer arithmetic, and its treads are decking bought on top of everything above.
How to take off a deck
Three steps, and the order of them is what keeps the frame and the surface agreeing with each other.
Measure the deck the way it will be framed
Two dimensions, and which is which matters more than either number. The length runs along the house, because that is the direction the boards run and therefore the length of every row. The width is the projection out from the house, because that is what the joists span and what the span table has to cover. Take the length from the face of the ledger, not from the siding: the siding stands off the band joist by half an inch or more and none of it is deck. On a wrap-around or an L, run the tool once per rectangle and add the results, because the joists in each leg run a different way.
Set the board face and the gap before you look at anything else
The gap is a covering dimension, not a detail. Five and a half inches of board on a quarter-inch gap covers five and three quarters of the run, so the two fields together decide the board count and nothing else does. Measure a board rather than trusting the label — capped composite is sold at 5.5, 5.4 and 5.36 in depending on the brand, and across a 16 ft width that difference is a whole extra row. Wet pressure-treated stock is the exception that catches people: it goes down almost tight because it shrinks across the face as it dries, so the default here is an eighth rather than a quarter.
Let the decking pick the joist spacing, then check the span
Choose the board first and the frame follows it, which is the opposite of the order most people build in their heads. Two-inch boards are allowed 24 in centers, 5/4 stops at 16, and turning either 45 degrees drops it a step because the board is now reaching further between bearings. Composite is not covered by that table at all — it is whatever the printed instructions say, usually 16 in across and 12 in on the diagonal. With the spacing set, the joist span check compares your projection against the published table for the species group you picked, and tells you which of the three ways out applies if it does not fit.
Technical specifications
| Board profiles | 5/4 x 6 and 2 x 6 wood at their 5 1/2 in dressed face, capped composite and PVC at a nominal 5 1/2 — and the face is editable, because brands ship 5.5, 5.4 and 5.36 in |
|---|---|
| Gap defaults | 1/8 in for wet pressure-treated, 1/4 in for dried wood, 3/16 in for composite; anything from 0 to 3/8 in is accepted |
| Joist spacing | 12, 16 and 24 in on center, checked against what the decking is rated for — 24 in for 2 in boards and 16 for 5/4 under IRC Table R507.7, 12 in once either turns 45 degrees |
| Joist span table | 36 published rows: 2 x 6 through 2 x 12, three species groups, three spacings, at 40 psf live plus 10 psf dead in wet service |
| Stock lengths | 8 to 16 ft for wood, 12, 16 and 20 ft for composite — every one costed against a single row, including the two-length mix when no board reaches |
| Cantilever check | One quarter of the joist's back span, the limit printed with the span table |
| Guard | 36 in high wherever the deck stands more than 30 in above grade, with balusters spaced so no opening passes a 4 in sphere |
| Data kept | None — the deck size, the board face and the species never leave the tab |
Frequently asked questions
How many deck boards does a 12 by 16 ft deck take?
Twenty-six rows of 16 ft board, plus a couple of spares. The 12 ft dimension is the one the boards cross: 144 inches of run, and a 5 1/2 in board on an eighth-inch gap covers 5 5/8 in of it, so 26 boards land across it with the last one ripped narrow. Buying 16 ft lengths means one board per row and no butt joints anywhere on the deck, which is worth more than the few dollars a mix of shorter lengths might save. Divide 144 by 5.5 and ignore the gaps, the way most calculators do, and you get 27 — one board you carry home, stand behind the shed and never use.
Do I gap wet pressure-treated decking?
Barely — an eighth of an inch at most, and plenty of builders lay it tight. A board that arrives dripping is at or near the fiber saturation point and will lose close to a quarter inch across a 5 1/2 in face over its first summer, so a quarter-inch gap laid wet opens into a three-eighths gap that swallows keys and dog claws. Kiln-dried, air-dried and composite boards go the other way and need the gap from day one. If you cannot tell which you have, weigh one: a soaking 5/4 x 6 x 16 is close to twice the weight of the same board dry.
Why does composite need joists at 16 in when my wood deck was at 24?
Because a composite board is a covering rather than a structural member, and it creeps. Wood carries a load and stops deflecting; a polymer-bound board keeps sagging slowly under the same load, so the manufacturers set the spacing themselves and the code defers to them instead of publishing a number. Sixteen inches across the joists and twelve on the diagonal is the usual pair, and stair treads are almost always held to twelve regardless. Two-inch nominal wood decking is the only surface on this page that the code lets out to 24 in.
Can I lay composite on the frame that is already there?
Only if the joists are at or inside the spacing your boards are rated for, and only after you have been under it with a screwdriver. This is the single most common resurfacing mistake: a 1990s deck framed at 24 in centers for 2 x 6 wood decking will take composite boards that then flex underfoot between every pair of joists, and the manufacturer's warranty is void the moment the spacing is wrong. Sistering an extra joist between each existing pair brings 24 in down to 12, which is the fix when the frame is otherwise sound — and this page counts that as a joist run at the new spacing.
How many screws does a deck take?
About three and a half per square foot with 5 1/2 in boards on joists at 16 in centers — roughly 350 in a 100 sq ft, which is also why a 5 lb box is the unit the aisle sells them in. The arithmetic is two per board at every joist it crosses, so it scales with the joist spacing rather than the area: the same deck framed at 12 in centers needs a third more, and one at 24 in needs a quarter fewer. Butt joints cost two extra each, because both board ends land on the same joist. Grooved boards on hidden clips run at one clip per crossing instead, which is half the count and none of it visible.
How far can a deck joist span?
Read it off the deck joist table in the code, not off the floor joist table — they are different numbers for the same board. A deck joist is wet service under a 40 psf live load with nothing but weather over it, and the published spans come out shorter than the same size would carry inside a house. A 2 x 8 of southern pine at 16 in centers is listed at 11 ft 10 in, so a 12 ft deck misses it by two inches and wants a 2 x 10, closer centers or a second beam. This page reproduces that table for three species groups so the check is in front of you, but a table on a web page approves nothing: the grade stamp on your actual boards, the hot tub you have not mentioned and your building department all outrank it.
The last board comes out as a two-inch strip. What do I do about it?
Change the gap — it is the free variable, and nobody has ever noticed a thirty-second of an inch spread across two dozen joints. A 12 ft width at a quarter-inch gap lands the twenty-sixth board as a quarter-inch sliver; open the gaps to about nine thirty-seconds and twenty-five full boards cover the same 144 inches with no rip at all. The other two answers are a picture-frame border, which turns the ragged edge into a deliberate one and hides the rip under the mitered perimeter board, and splitting the shortfall so the first and last rows are ripped to the same width. Decide before the first board goes down; it cannot be fixed at the far edge.
About counting a deck
A deck take-off has one arithmetic trap in it and almost every calculator on the web falls into it. Boards do not tile the deck; boards and gaps do. Five and a half inches of face on a quarter-inch gap covers five and three quarters of the run, so the gaps are doing 4.3 percent of the covering, and a page that divides deck width by board width orders 4.3 percent more boards than the deck can physically hold — three of them on a 30 ft run, bought, carried and stacked behind the shed. Counting it properly is not harder, it is just a different sum: n boards leave n minus one gaps between them, which is also the only way to find out what the last board rips to. That number is the one people care about once the deck is half down, because a two-inch strip along the outside edge is the first thing anyone sees, and it is entirely avoidable — the gap is a free variable and a thirty-second of an inch spread across two dozen joints is invisible.
The other thing worth getting right is the direction of the decision: the decking picks the joist spacing, not the other way round. IRC Table R507.7 lets 2 in nominal boards span 24 in between joists and holds 5/4 to 16, and turning either of them 45 degrees drops it a step because the board is now reaching further between bearings. Composite is not in that table at all — the code hands it back to the manufacturer's printed instructions, which is why the same 16 in you use for 5/4 wood is a rule rather than a code minimum, and why stair treads are usually held to 12. This is what makes a resurfacing job go wrong: a deck framed at 24 in centers in 1995 for 2 x 6 wood will happily accept composite boards that then flex between every pair of joists and void the warranty. It is also why the span check on this page reads off the deck joist table rather than the one for floors — a deck joist is wet service under a 40 psf live load, and the published spans come out shorter than the same board carries indoors. Reference, not approval: the grade stamp on your boards and your building department are the ones who decide.
Three things sit next to this page rather than inside it. The flight down to the yard has its own rise, run and stringer arithmetic, so take it through the stair calculator and add its treads to the decking order here. The walls of anything you build on the deck — a privacy screen, a pergola post wall — belong to the framing calculator, and the concrete that goes in the footing holes to the concrete calculator, which counts piers as a set rather than one at a time. If the yard is quoting rough or hardwood decking by volume instead of by the piece, the board foot calculator converts the list above into the unit on the invoice. And once a roof goes over the deck, the sheathing comes off the plywood calculator, the framing off the rafter calculator and the rafter length calculator, and the covering off the shingle calculator.
Where the deck dimensions go
Every number on this page is worked out by JavaScript running in the tab you are reading it in. Nothing you type — measurements, quantities, the prices your supplier quoted you — is uploaded, logged or kept, which is also why the calculators carry on working on a site with no signal.
The materials list prints as well as copies: the browser's print view drops the header, the ads and everything below the tool, and leaves the order and the stock-length table on the page. Nothing is generated on a server to make that happen, so it works on a phone with no signal in a yard.