Deck Board Calculator
Rows, linear feet and fasteners — plus which stock length wastes the least.
Deck boards
26 rows
- Deck area
- 192 sq ft
- Row pitch
- 5.625 in (board + gap)
- Linear feet
- 416 ft
- Buy with 10% waste
- 458 ft
- Joist crossings per row
- 13
- Deck screws
- 676 (about 3.8 lb)
Decking only. Framing, ledger, footings, railing and stairs are separate line items and usually cost more than the boards.
Finishing it afterwards? Use the wood stain calculator →
Boards to buy by stock length
| Stock length | Boards | Linear feet bought | Offcut | Full-length rows |
|---|---|---|---|---|
| 8 ft | 52 | 416 ft | 0 ft | No — boards butt mid-run |
| 10 ft | 52 | 520 ft | 104 ft | No — boards butt mid-run |
| 12 ft | 52 | 624 ft | 208 ft | No — boards butt mid-run |
| 16 ft | 26 | 416 ft | 0 ft | Yes — no butt joints |
| 20 ft | 26 | 520 ft | 104 ft | Yes — no butt joints |
Each row is counted separately because an offcut from one row is rarely long enough to start the next. The offcut column is the real cost of picking the wrong length: on a 12 ft run, 16 ft boards throw away a third of every board, while 12 ft boards throw away nothing and need no butt joints. Where a row does have to be butted, the joint must land on a joist with blocking or a doubled joist under it.
How this is calculated
pitch = board width(in) + gap(in) rows = ceil( (across(ft) × 12 + gap) / pitch ) linear ft = rows × row length(ft) crossings = floor( row length(ft) × 12 / joist spacing ) + 1 screws = crossings × 2 × rows (clips: × 1)
One gap is added back before dividing because the last row has no gap after it. It changes the row count on narrow decks and never hurts on wide ones. Board width is the actual face width: a 5/4 × 6 measures 5.5 inches, so using the nominal 6 would undercount the rows by about 9% and leave you short a board or two on a mid-sized deck.
Rows and linear feet per 100 square feet
| Board width | Gap | Pitch | Rows per 10 ft | Linear ft per 100 sq ft |
|---|---|---|---|---|
| 5.500 in | 0.1250 in | 5.625 in | 22 | 213 ft |
| 5.500 in | 0.1875 in | 5.688 in | 22 | 211 ft |
| 5.500 in | 0.2500 in | 5.750 in | 21 | 209 ft |
| 5.250 in | 0.1875 in | 5.438 in | 23 | 221 ft |
| 5.100 in | 0.1250 in | 5.225 in | 23 | 230 ft |
| 3.500 in | 0.1250 in | 3.625 in | 34 | 331 ft |
The linear feet column is the exact figure before rounding to whole rows, which is why it is useful for pricing and the row count is what you actually buy. Both come from the same arithmetic the calculator runs.
Frequently asked questions
How many deck boards do I need?
Divide the run across the joists by the board width plus the gap to get the number of rows, then multiply by the length of each row for linear feet. A 16 by 12 ft deck with boards running the 16 ft direction needs 12 ft ÷ 5.625 in, or 26 rows, which is 416 linear feet before waste. Buying that as 16 ft boards means 26 boards with no cutting at all, which is why matching stock length to deck length saves real money.
What gap should I leave between deck boards?
For kiln-dried wood, 1/8 inch — it will shrink and open up. For wet pressure-treated lumber, butt them nearly tight, because they shrink to roughly a 1/8 inch gap on their own within a season. Composite is the opposite: it expands with heat, and the manufacturer specifies the gap, usually 3/16 inch along the edge and more at the ends. Following the composite instructions is not optional, since the warranty depends on it.
How many screws per deck board?
Two per joist crossing, which at 16 inch joist spacing is roughly 350 screws per 100 square feet. Order by the pound rather than the count and expect about 175 to 190 deck screws in a pound for a 2.5 inch #8. Hidden fastener clips run one per joist crossing instead of two screws, and cost several times more per square foot — but they are what makes a hardwood or composite deck look finished.
Should deck boards run the long way or the short way?
Boards run perpendicular to the joists, so the direction is decided by how the framing runs, not by preference. Running them the long way means fewer rows and less cutting; running the short way means more rows but shorter, cheaper boards. If you want boards running a direction the joists do not allow, the fix is blocking or a second framing layer, not fastening across the grain of the structure.
How much waste should I add for deck boards?
Five to ten percent on a plain rectangle where you can buy boards the full deck length, and fifteen or more once you have angles, a picture frame border, stairs or boards that must be cut and butted mid-run. Butt joints have to land on a joist, so the offcut is rarely reusable at the other end. If a stock length matches your deck within a foot, take it — the waste factor exists mostly to cover the mismatch.
Do I need blocking under butt joints?
Yes, whenever two boards meet end to end. Each end needs its own bearing and its own fasteners, so a single joist under a butt joint gives each board barely three quarters of an inch of purchase. Either double the joist there or add blocking, and stagger the joints so they do not line up down the deck — a row of aligned butt joints is both a weak line and the first thing the eye sees.
Results are planning estimates for a rectangular deck. Angles, borders, stairs, and openings around posts all add material this does not account for. Follow the manufacturer instructions for composite spacing and fastening — the warranty depends on them.