Planning a new deck? Enter the size and pick your boards. You get the deck boards, joists, posts, footings and screws to buy, with extra for cuts already included.
Your shopping list
39Deck boards to buy
13Joists
3Posts and footings
- Deck area192 sq ft
- Rows of boards26
- Deck screws2 per board at each joist744
- Joist hangersOnly if joists hang from a ledger or beam13
Posts are counted at 8 ft apart. Joist and beam sizes depend on your lumber and local code. Extra of 10% is included.
How to use the Deck Calculator
- Measure the length and width of the deck. The boards run along the length.
- Pick your board width, board length and joist spacing.
- Choose one beam for a deck attached to the house or two for a free-standing deck, then read your list.
The math behind it
Rows of boards = deck width x 12 / (board width + 1/8 in gap), rounded up
Joists = deck length x 12 / joist spacing + 1, rounded up
Posts = beams x (deck length / 8 ft + 1), rounded up
Screws = rows x joists x 2 x (1 + extra %)
A worked example
What we typed in
- Deck length: 20 ft
- Deck width: 14 ft
- Board width: 5.5 in wide (5/4 x 6 or 2×6)
- Board length: 12 ft
- Joist spacing: 16 in apart (standard)
- Support beams: 2 beams (free-standing deck)
- Extra for mistakes and cuts: 10%
What we got
- Deck boards to buy: 55
- Joists: 16
- Posts and footings: 8
- Deck area: 280 sq ft
- Rows of boards: 30
- Deck screws: 1,056
- Joist hangers: 16
Tips from the job site
- Leave a 1/8 in gap between boards so water can drain.
- Joists 16 in apart suit most wood decking. Composite boards often need closer joists.
- Each post needs a footing, so open the Deck Footing Calculator next.
Common questions
How do I calculate how much decking I need?
Work out how many board rows fit across the width, then how many boards each row needs. Add about 10% for cuts.
How far apart should deck joists be?
16 in on center is the usual spacing. Use 12 in for diagonal boards or when the board maker asks for it.
See all Deck Calculators.