Decking calculator
Estimate decking boards from deck size and waste allowance.
What this calculator covers
Estimate how many decking boards a rectangular deck needs from its size, waste allowance, and the selected board coverage.
The walkthrough keeps the ordering math visible so users can see how deck area and waste become a board count.
Frequently asked questions
- What waste percentage should I use?
- A 10% allowance is a common starting point for straightforward rectangular decks. Diagonal layouts, picture framing, or decks with cutouts typically require 15% or more to avoid running short.
- What does board coverage mean in this calculator?
- Board coverage is the net square footage one board contributes to the finished deck surface after accounting for the gap between boards. Narrow, standard, and wide board options each have a different coverage value.
- Why does the calculator round board counts up?
- Boards can only be purchased as whole units. Rounding up ensures the material order is not short, even when the adjusted area divides unevenly by the coverage rate.
- Does this work for non-rectangular decks?
- The calculator models a simple rectangular footprint. For L-shaped or irregular decks, split the shape into rectangles, run the calculator for each section, and add the board counts together.
Tool
Run the calculation
Result
RESULT · DECKING
â„–020
Primary result
39 boards
A 16 ft by 12 ft deck with 10% waste needs about 39 decking boards at the selected board coverage.
- Deck area
- 192 sq ft
- Adjusted area
- 211.2 sq ft
- Boards needed
- 39 boards
Step-by-step solution
- 1.Find the deck area: 16 × 12 = 192 sq ft.
- 2.Add 10% waste to get an adjusted deck area that displays as 211.2 sq ft.
- 3.Divide the exact adjusted area by 5.5 sq ft per board and round up to 39 boards.
Walkthrough
Visual walkthrough
Decking planning starts with the deck footprint, adds waste for cuts and edge work, then converts that area into boards based on the selected coverage rate.
01
Measure the deck footprint
16 × 12 = 192 sq ft
Length times width gives the base decking coverage area.
02
Add a waste allowance
Deck boards need waste coverage for cuts, picture framing, and layout adjustments, and the displayed adjusted area is rounded for readability.
211.2 sq ft adjusted area
03
Convert area into boards
The exact adjusted area is divided by the board coverage rate and rounded up so the material order is not short.
39 boards needed