Decking Calculator — How Many Deck Boards?
Enter your deck dimensions and the size of your deck boards. This calculator figures out how many rows fit, the total linear feet, and how many boards to buy including waste.
How to use this calculator
- Enter the deck length (the direction the boards run) and width (across the board ends), in feet.
- Choose your board width — 5.5 in is the actual width of a nominal 6-inch board.
- Set the gap between boards; 1/8 inch is standard for drainage and expansion.
- Pick the board length you can buy; the calculator adds 10% waste and rounds up.
The formula
Decking is bought as boards of a fixed length, so we find the total run of decking and divide.
Each row occupies (board width + gap). Rows = deck width ÷ (board width + gap), rounded up.
Linear feet = rows × deck length. Add 10% for cuts and waste.
Boards = linear feet ÷ board length, rounded up to whole boards.
Worked example
A 16 ft × 12 ft deck, 5.5 in boards, 1/8 in gap, 16 ft boards.
Row width = (5.5 + 0.125) ÷ 12 = 0.469 ftRows = 12 ÷ 0.469 = 25.6 → 26 rowsLinear feet = 26 × 16 = 416 lin ftWith 10% waste = 458 lin ftBoards = 458 ÷ 16 = 28.6 → 29 boards
You need about 29 boards of 16 ft decking for this 16×12 deck.
Frequently asked questions
How many deck boards do I need?
Divide the deck width by (board width + gap) to get the number of rows, multiply by the deck length for linear feet, add 10% waste, then divide by your board length.
What gap should I leave between deck boards?
Leave about 1/8 inch between boards for drainage and airflow. Pressure-treated boards installed wet can be butted tighter since they shrink as they dry.
What is the actual width of a 6-inch deck board?
A nominal 5/4×6 or 2×6 deck board is actually 5.5 inches wide. Always calculate with the actual width, not the nominal size.
Does this include framing or fasteners?
No — this estimates the deck boards only. Joists, beams, and hidden fasteners or screws (about 350 screws per 100 sq ft) are separate.