HesapHanem

Deck Board Calculator

Find how many deck boards to buy.

How it is calculated

The tool compares areas: boards = ⌈(deck length × deck width) ÷ (board length × board width)⌉, rounded up to a whole board. It then adds a 10% waste allowance, ⌈boards × 1.1⌉, for cuts, offcuts and damaged pieces. All four dimensions must be in metres, since the deck area is reported in m², and each must be greater than zero. The calculation is purely by area: it ignores the gap between boards, the way boards are laid across joists, and offcuts that cannot be reused, so board width should be the width you actually cover.

Worked example

A deck is 4 m by 3 m, so its area is 12.00 m². One board is 2.4 m long and 0.14 m wide, covering 0.336 m². Then 12 ÷ 0.336 = 35.7, which rounds up to 36 boards. With the 10% allowance, 36 × 1.1 = 39.6, rounded up to 40. You should buy 40 boards.

Try this example →

Common mistakes

  • Entering the board width in millimetres or the length in feet. All values are metres, so a 140 mm board is 0.14.
  • Using the nominal board width and ignoring the gap left between boards, which can leave you a few boards short on a large deck.
  • Assuming each board is used in full. Where the deck is longer than the board, cuts and joints at the joists create waste, which the 10% allowance only roughly covers.
  • Buying the exact first figure for a deck with angles, stairs or borders. Those extras are not included and need to be added separately.

About this calculator

This calculator figures out how many deck boards you need to buy by dividing the deck's total surface area (or the coverage width of a single board multiplied across the deck's width) by the area of one board (board length × board width) — the gap between boards is not modelled, so enter the width the board actually covers — then rounding up and adding a fixed 10% waste allowance to cover cutting losses, mistakes and damaged pieces.

DIY homeowners and professional deck builders use this before ordering lumber or composite decking material to avoid running short mid-project (which risks a mismatched dye-lot on a second order) or over-ordering and wasting money. Getting the board count right also depends on the chosen decking pattern (straight, diagonal or herringbone increases waste), the board length available from the supplier, and the joist spacing the boards need to span.

Was this helpful?

You can pick up to 3 reactions.

Comments (1)

  • Editorial team

    Board length matters more than the area figure suggests. If your deck is 4.8 m along the boards, 2.4 m boards fit twice with nothing cut off, so the 10 percent allowance may be generous. At 4.0 m, each row of 2.4 m boards leaves a 0.8 m offcut that may be too short to reuse, so waste runs higher. Sketch the layout before ordering. What deck size and board length are you planning around?

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators