Decking Calculator
Enter your deck's dimensions and your board's width and length to find how many boards to buy.
How deck board quantity is calculated
Deck area is length × width. Each board covers an area equal to its width × length, so dividing the deck area by a single board's area gives the exact number of boards needed with zero waste.
In practice, boards get cut to fit the deck's edges and any obstacles, so a waste allowance (commonly 10%, more for complex layouts or diagonal patterns) is added before rounding up to a whole number of boards.
Frequently asked questions
Should I account for gaps between boards?
This calculator doesn't add gap spacing between boards — for very precise ordering, you could slightly increase the board width used in the calculation to include a typical 3-5mm expansion gap, though the waste allowance usually covers this.
How much extra should I buy for a diagonal decking pattern?
Diagonal patterns create more waste from angled cuts — consider increasing the waste allowance to 15-20% instead of the standard 10% for a straight layout.
Does this account for the direction boards run relative to the joists?
No — this calculator only computes area-based board count. The direction boards run affects joist spacing requirements, which is a separate structural consideration.