Deck Board Calculator
Estimate decking materials in a minute. Enter the deck size and board details to get the number of deck boards, joists, linear footage and screws, plus the material cost.
Deck boards needed
How to calculate deck boards
- Enter the deck length in the direction the boards run, and the width across them.
- Choose the board width and the gap. Most decking uses a 3/16 inch gap for drainage; composite manufacturers specify their own.
- Choose the board length you will buy and your joist spacing. Composite decking often requires 12-inch spacing; check the product instructions.
Deck materials explained
The number of rows is the deck width divided by the board width plus gap. If the deck is longer than one board, each row needs extra boards, with joints staggered and always landing on a joist. Buying boards that match the deck length (or divide evenly into it) saves the most waste.
Joists run perpendicular to the boards. 16 inches on center is standard for wood decking; most composite and PVC boards require 12 inches, and diagonal decking needs closer spacing still. This calculator counts joists only; beams, posts, footings and ledger boards depend on your design and local building code.
Each board is fastened with two screws at every joist it crosses, which works out to roughly 350 screws per 100 square feet at 16-inch spacing. Hidden-fastener systems use clips instead. Most areas require a permit for decks attached to the house or more than about 30 inches above the ground.
Need a different tool? Suggest it here — we read every message.
Frequently asked questions
How many deck boards do I need for a 12 × 16 deck?
With 5.5-inch boards, a 3/16 inch gap and 16 ft boards running the 16 ft direction, about 26 boards, or 29 with 10% waste.
What gap should deck boards have?
About 3/16 inch for kiln-dried wood and composite. Wet pressure-treated boards are often butted tight because they shrink as they dry.
How many screws per deck board?
Two at every joist. A 16 ft board across 16-inch joists needs about 26 screws.
Do I need a permit?
Usually, especially for attached or elevated decks. Check with your local building department.