Deck Calculator

1. Enter deck dimensions. Measure or plan the overall length and width of the deck in feet. Length is the direction the boards run, and width is the span they cross. A 16 ft × 12 ft deck is a common size for a backyard entertaining area.
2. Set board width. The default 5.5 inches is the actual width of a standard 2×6 or 5/4×6 deck board. Narrower boards (3.5 inch actual for 2×4s) mean more boards needed. Some composite decking is 5.4 or 6 inches wide, so check the product spec sheet.
3. Set board length. Choose the board length that best fits your deck. Using boards that span the full length of the deck in one piece minimizes end-grain joints that can collect water. Common lengths are 8, 10, 12, and 16 ft.
4. Enter price per board. This field is optional. Enter the retail or contractor price for each board to get a total material cost estimate. Note that this is deck board material only and does not include framing lumber, hardware, concrete footings, or labor.

Example: a 16 ft × 12 ft deck using 5.5-inch-wide boards in 8 ft lengths needs approximately 38 boards with a 10% waste factor, at a material cost of around $456 if boards are $12 each.

Deck boards are calculated by determining how many rows span the width and how many board lengths cover the deck length. A 10% waste factor accounts for end cuts, splits, and defects.

This calculator covers decking boards only. A complete deck project also requires: joists (typically 2×8 or 2×10 at 16 inches on center), beams, posts, concrete footings, joist hangers, screws, and ledger board hardware. A rough rule of thumb for total deck material cost (framing plus decking) is 1.5 to 2 times the decking board cost alone.