HowMuchIt / Deck
How many deck boards do I need?
A deck board is 5.5 inches wide whatever its name, and it comes in 12, 16 or 20 foot lengths. From the deck's size, the calculator counts the boards, the joists under them and what holds them down.
Work out your deck boards
| Step | How |
|---|---|
| Deck area | length x width, each platform on its own; stairs counted apart |
| One board | board length x 5.5 in / 12 (a 16 ft board covers about 7.3 sq ft) |
| Boards | deck area / one board, plus about 10 percent |
| Screws | 2 at every joist each board crosses |
| Hidden clips | about 90 to 100 per 50 sq ft |
5/4x6 and 2x6 boards are both 5.5 in wide, in wood and in composite.
Measure before you sketch
Measure the deck as a plain rectangle: the length the boards will run along, and the width across them. A deck with two levels or an L shape is two rectangles; do each one and add the boards. Stairs are counted on their own, tread by tread. If you can, choose a board length that matches the deck's length, or splits it in even pieces: a 16 foot deck with 16 foot boards has no joints to line up and much less waste.
Gaps, joists and screws
Boards are not laid tight. Composite boards are usually gapped 3/16 inch side to side, and dry wood about 1/8 inch, so water drains and the boards can move. Under them, joists are normally no more than 16 inches apart, center to center; boards laid on a diagonal need them every 12 inches, which means more joists for the same deck. Each board gets two screws at every joist it crosses. Hidden clips are sold by the pack, about 90 to 100 for every 50 square feet. Your board maker's guide has the final word for its own boards.
Questions people ask
How many deck boards do I need for a 12 x 12 deck?
A 12 by 12 deck is 144 square feet. A 12 foot board covers 12 times 5.5 inches, about 5.5 square feet, so 144 / 5.5 is about 26 boards, and 29 with ten percent extra. Type 12 and 12 with 12 foot boards to see it.
How far apart should deck joists be?
No more than 16 inches on center for boards laid straight across them, 12 inches for diagonal boards.
Should deck boards be spaced or laid tight?
Spaced: about 3/16 inch for composite, about 1/8 inch for dry wood. Check your board maker's guide, which may ask for more in shady, damp spots.
How many screws do I need for a deck?
Two at every joist each board crosses. A 16 foot deck on joists 16 inches apart has 13 joists, so each row of boards takes 26 screws.
Good to know
- Nominal 5/4x6 and 2x6 deck boards are both 5-1/2 in (5.5 in) wide, in wood and in composite.1,2,3
- Composite deck boards are sold in 12, 16 and 20 ft lengths.2,3,4
- Boards needed = deck area divided by the area of one board (board length x board width in feet), then add the waste allowance.2,3
- Measure the deck as length times width; for several platforms or odd shapes, measure each part and add them, and count stairs separately.2,3
- For a straight layout, add about 10 percent extra boards for waste, off-cuts and mistakes.3,5,6
- Composite deck boards are typically gapped 3/16 in side to side.3,7
- Dry wood deck boards are spaced about 1/8 in apart.8,9
- Joists under deck boards are normally spaced no more than 16 in on center.10,11
- Boards laid diagonally (45 deg to the joists) need joists 12 in on center.10,11
- Face-fastened boards take two screws (or two nails) at every joist they cross.8,12,13
- Hidden-clip packs are sized at about 90 to 100 clips per 50 sq ft of decking, close to 2 clips per square foot.14,15
How we checked this page
Checked on October 27, 2026. We kept a fact only when two independent publishers agree, and each one is numbered to its sources below. Where sources give different numbers, we keep only what they share. We never write a price. This page was written with an AI assistant and checked against the sources below.
Sources
- Decking, Siding and Dimensional Lumber Sizes, Mataverde Decking
- How Many Deck Boards Do I Need?, Trex
- How to Calculate How Much Decking You Need, TimberTech
- How to Build a Deck - Decking, Decks.com
- Deck Calculator: How Much Decking Do I Need?, Angi
- Pro Tip: Estimating Wood Decking Material Quantities, Mataverde Decking
- How to Space Deck Boards, Trex
- Prescriptive Residential Wood Deck Construction Guide (DCA 6), American Wood Council
- Deck Board Spacing by Material: What to Know, TimberTech
- How to Install Deck Joists, Trex
- Deck Floor Joist Spacing 101: How Far Apart to Place Your Joists, TimberTech
- DIY Resources Chapter 3: TimberTech Composite Installation with CONCEALoc, TimberTech
- How to Calculate the Number of Screws Required for a Deck, Hunker
- Hidden Fasteners - Universal (box), Trex
- TimberTech Fasteners sell sheet 2024 (copy on Doman CDN), TimberTech