Deck Calculator
Estimate deck boards, joists, fasteners, and cost for your project. Build a clear deck material shopping list before you buy.
This page covers deck surface materials first. Estimate stairs, railing, and footings separately so your main deck list stays accurate.
Last updated: March 25, 2026
Enter Your Deck
Boards run along this dimension (long side).
Joists run along this dimension.
1" thick, 5.5" actual width — common deck board
Pick the stock length you plan to buy. It changes your shopping list, not your deck area.
Hidden fasteners give a cleaner look. Screws are simpler and more common for standard wood decks.
Joists are the beams under the deck boards. 16" on center (OC) is standard — OC = spacing from one joist center to the next.
Use 10% for simple rectangles and closer to 15% for layouts with more cuts, waste, or picture-frame details.
Results
Use this list first when ordering deck boards, fasteners, and joist lumber.
Area is shown as a quick planning check. The shopping list above is the main output on this page.
- • Use a deck stair tool for stringers, tread count, and stair layout.
- • Use a concrete or post-hole tool for footing volume and hole depth.
- • Keep railing, balusters, and permits out of this first-pass shopping list and estimate them separately.
Project Examples
12×12 Platform Deck
144 sq ft · 5/4×6 boards · 16" OC
A simple square platform deck is the baseline case. Use it to estimate boards, joists, fasteners, and a clean 10% waste order before buying.
20×12 Attached Deck
240 sq ft · 5/4×6 boards · 16" OC
A larger attached deck shows why shopping-list outputs matter. If you switch from 16 ft stock to 12 ft stock, the purchase count jumps even when the deck size stays the same.
16×20 Composite Deck
320 sq ft · composite-style boards · 12" OC
Composite projects often push you toward tighter joist spacing and hidden fasteners, so spacing and hardware choice belong in the planning workflow.
How to Use This Deck Calculator
- Measure the deck surface — Enter length and width in feet. This page is for the main deck surface, not stairs or footings.
- Choose your board type — 5/4×6 is the standard deck board. 2×6 is thicker, and 2×4 usually means more pieces for the same area.
- Set joist spacing — 16" on center is the standard starting point. Tighten to 12" when product specs or usage demand it.
- Add waste — Use 10% for simple layouts and closer to 15% for diagonal boards, picture-frame borders, or heavy cutting.
- Review the shopping list — You get board count, boards per row, fastener planning, joist count, purchased linear feet, and an optional cost estimate before you buy.
How We Calculate Deck Materials
Calculated per AWC design guidelines. American Wood Council
Deck Planning Guide
This page includes
Deck boards, joist count, fastener planning, waste, and optional cost so you can build a first-pass deck material shopping list.
Estimate stairs separately
Use the deck stair calculator for stringers, tread layout, and stair geometry. Those rules should not be mixed into the main deck surface estimate.
Estimate footings separately
Use a concrete or post-hole calculator for footing volume. Post count, hole depth, and diameter belong in a separate footing workflow.
Raise waste for complex layouts
Straight rectangular decks can often use 10% waste. Diagonal boards, picture-frame borders, and lots of short cuts usually need closer to 15%.