About this calculator
Free Deck Calculator - Calculate decking materials needed.
How to use
Enter your values in the fields above and click Calculate to see your results. Click Clear to reset all fields.
What the deck calculator does and when to use it
This calculator converts the footprint of a deck into the total linear feet of decking boards needed to cover it. You enter the deck length and width in feet and the face width of the boards in inches, and it returns how many running feet of board would cover the surface with boards butted edge to edge. It is meant for the first-pass question every deck project starts with: roughly how much board do I need to price out?
Use it when comparing board widths, checking a supplier quote, or turning a sketch into a shopping list. Because the result is a single running-foot figure, you can divide it by the board length you plan to buy (8, 12, 16 or 20 feet) to get a board count. Remember that it estimates surface coverage only. It does not include joists, beams, posts, fasteners, railings or stairs, and it does not add any allowance for waste or spacing gaps.
The formula and its variables
- L is the deck length in feet and W is the deck width in feet.
- A = L × W is the deck area in square feet.
- b is the board face width in inches, and b / 12 converts it to feet.
- Linear feet = A / (b / 12), rounded up to the next whole foot.
The logic is that each linear foot of board covers b / 12 square feet, so dividing the area by that coverage gives the running length required. The board width is the actual face width, not the nominal size. A board sold as 6 inch decking usually measures about 5.5 inches across, and that difference changes the answer noticeably.
Worked example
Suppose a deck is 12 ft long and 16 ft wide and you plan to use boards 5.5 inches wide. The area is 12 × 16 = 192 square feet. Each board covers 5.5 / 12 = 0.4583 square feet per linear foot. Dividing, 192 / 0.4583 = 418.9, which the calculator rounds up to 419. The result shown is Linear Feet of Decking: 419 ft.
To turn that into boards, 419 divided by 16 is 26.2, so you would need at least 27 boards if each is 16 feet long and runs the full 16-foot dimension of the deck. In practice you would add extra for waste and a cutoff plan, since the calculator has none built in.
Common mistakes and how to interpret the result
- Using nominal instead of actual width. Entering 6 when the real face is 5.5 understates the linear feet by about 8 percent.
- Forgetting the gap. Boards are normally spaced about 1/8 to 1/4 inch apart for drainage and expansion. This tool assumes zero gap, so a slightly higher board count than shown is normal. Try the deck board spacing calculator to account for it.
- Skipping waste. End cuts, defects and pattern layouts such as diagonals typically call for extra material, commonly 5 to 15 percent. Add it after this result.
- Mixing units. Length and width are in feet but board width is in inches. Do not enter the board width in feet.
Related tools: Deck Board Spacing Calculator, Lumber Cutting Waste Calculator, Square Footage Calculator and Staircase Calculator for the steps that usually come with a deck.