Deck Board Calculator
Give it the deck, the face width of the board, the gap you are laying to and the length of the stock you are buying, and it returns the rows, the boards and the offcut. The gap is counted between every pair of rows and never after the last one, and the row that does not land flush is shown rather than hidden: you see the width the final board is ripped to, or, if you would rather stop at the last whole board, how much of the span is left bare. Fractions are typed the way a lumber yard prints them, so 1/8, 3/16 and 5 1/2 all read as measurements, and the whole takeoff runs in your browser with no account and nothing uploaded. Counts use exact decimal or fraction arithmetic for independent straight rows, with no cross-row offcut reuse, saw kerf or staggered join plan. Wood and composite use the actual face width you supply. Spacing selection, nominal 5/4 sizing, angled layouts, provider products and installed or replacement costs are not calculated.
deck12 ft x 16 ftboard5.5 in wide, 0.125 in gapstock12 ft, along the length, straight lay
- Rows
- 1 ripped
- Boards
- of 12 ft
- Linear ft
- Waste
- 4 boards
Use the actual board face and your supplied gap and stock length. Yard fractions such as 1/8 and 5 1/2 are exact. Unit changes preserve the same dimensions as complete decimals or fractions. The opening gap and waste are examples. This page counts straight rows; it does not choose board spacing or create angled, staggered or optimized cut layouts.
Complete selectable calculation
- The last row is ripped to 3/4 in after 34 full rows. The gap is counted between rows only.
- 1 stock boards per row, rounded up independently for every row. Cross-row offcut reuse, saw kerf, end gaps and a staggered join plan are not modeled.
- Supplied 10% waste adds 4 whole boards, rounded up, to 35 boards before allowance. The opening 10% is an editable example, not a recommendation.
- Stock for the rows totals 420 ft; row length totals 420 ft; the difference is 0 ft. This length difference excludes spare boards and side-rip material.
- Use actual face width and stock length for wood or composite. Board thickness, nominal 5/4 sizing, joist spacing, span, fixings, structural design, provider products and installed prices are not calculated.
- Decimal displays round half up to three places. < marks a positive value below half the last displayed place; an ellipsis marks abbreviation. The complete exact values are in the selectable calculation.
Common questions
- How many deck boards do I need for a 12 by 16 foot deck?
- With 5 1/2 inch boards and a 1/8 inch gap, boards running along the 12 foot side, the rows cross the 16 foot side, which is 192 inches. The row pitch is 5.625 inches, so 34 full rows plus their gaps cover 191 1/8 inches and leave 7/8 of an inch. Take one gap out of that and the final board is ripped to 3/4 in, which makes 35 rows in all. On 12 foot stock that is 35 boards and 420 linear feet, and a 10 percent waste allowance rounds it up to 39 boards. Change any of those figures and the count follows.
- Does the gap between the boards change how many I need?
- Yes, and it is counted at every row. The pitch of a row is the board face plus one gap, so a 6 inch board with a 1/4 inch gap repeats every 6.25 inches: over a 6 foot span that is 11 full rows instead of the 12 you get laying the same boards tight, and the leftover becomes a 3 1/4 inch rip. The gap is only counted between rows, never after the last one, because the deck ends on a board.
- What happens to the last row when the deck does not divide evenly?
- Rip to fit adds a row only when the remaining span, after one gap, has a positive board width. Whole boards reports the bare strip instead. On the 12 by 16 foot example that is a 3/4 in rip or a 7/8 in bare strip. A remainder no wider than one gap stays bare. Short displays use exact sixteenth fractions where available, otherwise rounded decimals; a positive tiny value is marked with <. The complete selectable calculation retains the exact width as a full decimal or fraction.
- How much extra should I allow for a diagonal deck?
- An earlier aggregate estimate used 15 percent extra for a 45 degree lay. That fixed allowance was not verified and is not offered as a takeoff here. Angled rows have different cut lengths, so an area divided by row pitch does not establish how many stock boards a cut layout needs. This page now counts straight rectangular rows only; it does not create diagonal, staggered or optimized cutting plans. Enter the waste allowance supplied for your straight-row calculation; the opening 10 percent is an editable example.
- Can it work out joist spacing or how far a board will carry?
- No, and it is built not to. This is a material takeoff: it counts rows, boards and offcut for the deck you describe. It holds no span table and sizes no joist, and nothing here is a fixing schedule. Those numbers come from your local building code or from the person specifying the job, and a figure we estimated is not one to build on.
- Can I work in metres, and does it remember my deck?
- The units control switches between feet with inches and metres with millimetres using exact definitions: 12 ft becomes 3.6576 m, 5 1/2 in becomes 139.7 mm and 1/8 in becomes 3.175 mm. Complete decimals or fractions preserve the same measurements. Saved drafts restore without being rewritten. Only valid deliberate changes save, while unrelated saved fields are retained; damaged or conflicting records stay untouched. Forget saved settings removes the saved record while leaving the current calculation on screen. Nothing is uploaded and no account is needed.
Exact arithmetic on the dimensions you enter, including the gap. It estimates material only and makes no span, joist or structural recommendation.