Deck Board Chart: Boards and Joists by Deck Size

Fourteen common deck sizes with the board count, the linear feet and the joist count for each. The same deck in 12, 16 and 20 foot stock, and in three board widths.

A deck board count is not the area divided by the board. It is the number of rows across the width, each row being one board length long, and the gap between boards is part of that arithmetic. A quarter inch gap on a 16 foot wide deck takes a whole board out of the count, so leaving it out of the arithmetic buys one board too many and plans a last row that will not land where you drew it.

The first number in each deck size is the direction the boards run, which is normally parallel to the house. Turn the boards and the count changes, so the second and third tables are worth reading before the lumber gets ordered.

Boards, linear feet and joists at common deck sizes

Deck size	Area (sq ft)	Rows of boards	Linear feet	16 ft boards	Joists at 16 in oc
10 x 8 ft	80	17	170	11	9
12 x 8 ft	96	17	204	13	10
12 x 10 ft	120	21	252	16	10
12 x 12 ft	144	26	312	20	10
14 x 12 ft	168	26	364	23	12
16 x 10 ft	160	21	336	21	13
16 x 12 ft	192	26	416	26	13
16 x 14 ft	224	30	480	30	13
16 x 16 ft	256	34	544	34	13
20 x 12 ft	240	26	520	33	16
20 x 16 ft	320	34	680	43	16
20 x 20 ft	400	42	840	53	16
24 x 16 ft	384	34	816	51	19
24 x 20 ft	480	42	1,008	63	19

Boards 5.5 inches wide, which is a 5/4 x 6 or a 2 x 6, with a quarter inch gap. Joists 16 inches on center, counted along the length with one at each end. Nothing here includes waste, a picture frame border, stairs or a rim joist.

Board count by the stock length you buy

Deck size	12 ft boards	16 ft boards	20 ft boards
10 x 8 ft	15	11	9
12 x 8 ft	17	13	11
12 x 10 ft	21	16	13
12 x 12 ft	26	20	16
14 x 12 ft	31	23	19
16 x 10 ft	28	21	17
16 x 12 ft	35	26	21
16 x 14 ft	40	30	24
16 x 16 ft	46	34	28
20 x 12 ft	44	33	26
20 x 16 ft	57	43	34
20 x 20 ft	70	53	42
24 x 16 ft	68	51	41
24 x 20 ft	84	63	51

Boards 5.5 inches wide with a quarter inch gap. Where the stock length does not divide into the deck length the count rises, because the offcut from one row will not usually reach across a second.

Boards needed at three board widths

Deck size	3.5 in face	5.5 in face	7.25 in face
10 x 8 ft	17	11	9
12 x 8 ft	20	13	10
12 x 10 ft	24	16	12
12 x 12 ft	30	20	15
14 x 12 ft	35	23	18
16 x 10 ft	32	21	16
16 x 12 ft	39	26	20
16 x 14 ft	45	30	23
16 x 16 ft	52	34	26
20 x 12 ft	49	33	25
20 x 16 ft	65	43	33
20 x 20 ft	80	53	40
24 x 16 ft	78	51	39
24 x 20 ft	96	63	48

Face width, not nominal size. A 2 x 4 is 3.5 inches, a 5/4 x 6 and a 2 x 6 are both 5.5, a 2 x 8 is 7.25. Counted at 16 foot stock with a quarter inch gap.

Print this chart

The same table on a sheet of paper, for the truck door, the trailer wall or the back of a clipboard. No signup and no watermark.

PDF .pdf

Free, no signup, no email, no watermark.

Need one exact answer instead?

The deck calculator takes your own measurements and returns the number for your job, plus the material list as a printable document. Every cell in the table above came out of that same calculator, run at build time.

Measure the face, not the name

Lumber is named by a size it has not been since it left the saw. A 2 x 6 is 5.5 inches wide, a 5/4 x 6 is also 5.5, and a composite board sold as a 6 inch board is usually 5.5 as well. Use the face width, which is what the tape measures on site.

Composite and PVC boards are the exception worth checking. Several of the common brands run 5.36 or 5.5 inches, and a few grooved boards are narrower once the hidden fastener sits in the groove. A sixteenth of an inch across forty rows is a board.

The gap is not optional and it is not decoration

A quarter inch gap between boards lets water off the deck and lets the boards move. Wood decking installed wet will shrink and open the gap further, and decking installed dry will swell and close it, which is why a kiln dried board goes down tighter than a wet treated one.

Composite decking has manufacturer gap requirements that are not a matter of taste, and they change with the temperature the boards were installed at. Missing them voids the warranty, which is the part that gets expensive.

What this count does not include

This is the field of the deck. It does not count a picture frame border, which adds one or two boards per side and changes the field dimension underneath it. It does not count stairs, which take their own treads. It does not count the rim and the ledger.

Add five to ten percent for waste on a rectangular deck and more on anything with an angle or a curve in it, because every cut that is not square produces an offcut nothing else will use.

Joists carry the span, not the board count

The joist column here is a count at 16 inches on center for ordering purposes. It is not a span table and it does not decide what size joist the deck needs, which depends on the species, the grade, the span, the load and the local code.

Twelve inches on center is common under a diagonal deck board layout, because the diagonal run increases the effective span between bearing points. The calculator takes any spacing.

Questions people ask

How many deck boards do I need for a 12 x 16 deck?

About 26 boards of 16 foot 5/4 x 6, with the boards running the 16 foot way and a quarter inch gap. Running them the 12 foot way instead takes 34 boards of 12 foot stock.

How do you calculate deck boards?

Divide the deck width in inches by the board face width plus the gap, and round up. That is the number of rows. Multiply rows by the deck length to get linear feet, then divide by the stock length you are buying.

How many deck boards in a square foot?

Roughly 2.1 linear feet of 5.5 inch board per square foot of deck with a quarter inch gap, so a 200 square foot deck is about 420 linear feet.

Should deck boards run parallel or perpendicular to the house?

Parallel to the house is the usual choice because it puts the joists perpendicular to the ledger, which is how the framing normally wants to run. A diagonal layout looks good and costs about fifteen percent more material plus tighter joist spacing.

How much waste should I add to a deck board order?

Five to ten percent on a plain rectangle. More on anything with a picture frame, an angle, a curve or a stair, because those cuts leave offcuts that will not go anywhere else.

More reference charts

Fence post chartTwelve fence lengths at three post spacings, then the whole material list at eight foot spacing, then the concrete a hole takes at every normal depth and diameter.Insulation coverage chartFourteen wall and ceiling areas against six package coverages, and the cavity area that is actually left once the framing is taken out of the gross square footage.Roof pitch chartEvery pitch from 1/12 to 24/12, with the angle, the multiplier you have to apply to a footprint, and the rafter length that goes with it.Roof squares chartFifteen common footprints against six pitches, so you can find a house roughly the size of the one in front of you and see the squares before you measure anything.Siding squares chartTen wall perimeters against six wall heights, with the waste already added, so you can price the walls before you have measured a single gable.Gable area chartEvery gable width from 16 to 48 feet at five pitches, so the triangle nobody can reach with a tape stops being a guess.

See all 30 reference charts.