Deck Board Calculator
Find out how many deck boards to buy for your deck — gap and waste included.
Last reviewed 2026-06-06
Decking is sold as boards of a fixed length, but you measure a deck by area — and the small gap between boards quietly changes the count. This calculator bridges all of that.
Enter the deck size, the board width and the length of board you plan to buy, plus the gap between boards. We work out the linear length of decking, add waste, and tell you how many boards to order.
How to use the Deck Board Calculator
- Measure the deck length and width.
- Enter your board width (a “5/4×6” board is about 5.5 in / 14 cm wide).
- Set the gap between boards (about 1/8 in / 3 mm is common).
- Choose the board length you’ll buy and a waste allowance, then read the board count.
Frequently asked questions
How many deck boards do I need?
Divide the deck area by the effective board coverage (board width plus the gap), which gives the total linear length of decking. Divide that by your board length and add 10% for waste. This calculator does all of it automatically.
What gap should I leave between deck boards?
About 1/8 inch (3 mm) is typical for dry boards, allowing drainage and airflow. Pressure-treated boards that are still wet can be butted tighter because they shrink as they dry.
How much extra decking should I buy?
Plan for about 10% waste on a simple rectangular deck, and up to 15% if you have angled boards, a picture-frame border, or lots of cuts around stairs and posts.
What size are deck boards?
A very common decking board is nominal “5/4×6”, which is roughly 1 inch thick and 5.5 inches (14 cm) wide. Composite and hardwood boards vary, so measure or check your product and update the width field.