Deck Calculator
Estimate how many deck boards and joists you need for any deck size. Choose board type and joist spacing, then get a material list and optional cost estimate.
You'll get: how many boards and joists to buy, plus total linear feet — everything you need for a shopping list.
Last updated: February 23, 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
Length you plan to buy (e.g. 12 ft). Board count above is total linear feet — this doesn't change the result.
Joists are the beams under the deck boards. 16" on center (OC) is standard — OC = spacing from one joist center to the next.
10% for simple rectangles; 15% for cuts and waste. Adds extra for cutting mistakes so you don't run short.
Results
Material list
- • Buy joist lumber in lengths that match or exceed 12 ft to avoid splices.
- • 16" OC joists suit most deck boards; use 12" for composite or heavy loads.
- • Check local codes for beam size, footings, and permits.
How to Use This Calculator
- Measure or plan your deck — Length × width in feet. Use a preset (e.g. 12×12) or enter custom dimensions. Boards run along the length; joists run along the width.
- Choose board type — 5/4×6 is the standard deck board. 2×6 is thicker; 2×4 uses more boards. The calculator uses exposed width (with a typical 1/4" gap) to count boards.
- Set joist spacing — 16" on center is standard. Tighter (12") for composite or heavy use; 24" only when the product allows.
- Add waste — 10% for simple layouts; 15% if you have many cuts or angles.
- Review results — You get board count, decking linear feet, joist count and lumber linear feet. Turn on cost estimate to add material and labor prices.
How We Calculate
Joists = (Length in inches ÷ Joist spacing) + 1, then × (1 + Waste%)
Calculated per AWC design guidelines. American Wood Council