How to use this calculator
Start by entering your deck length and width in feet. Then select your board size (such as 5/4x6 or 2x6) and choose a board length that matches what is available at your lumber yard. The calculator uses these dimensions to determine how many boards you need to cover the deck surface.
Next, select your joist spacing. Most residential decks use 16 inches on center, but composite decking and diagonal layouts often require 12 inch spacing for better support. The calculator will tell you how many joists you need in addition to the deck boards.
The results include total board count, linear feet of lumber, number of joists, and an estimate of the screws required. If you enter a price per board, you will also see a total materials cost. The calculator automatically adds a waste factor to account for cuts and defective boards.
Use this estimate to create your shopping list before visiting the lumber yard. Having accurate quantities saves time and reduces the number of return trips for additional materials.
Choosing the right deck board material
Pressure treated lumber is the most affordable option and works well for most residential decks. It resists rot and insects but requires regular staining or sealing every one to three years. Cedar and redwood are naturally rot resistant and offer a beautiful appearance, but they cost more and still need periodic maintenance.
Composite decking is made from a blend of wood fiber and plastic. It costs two to three times more than pressure treated lumber upfront, but it requires almost no maintenance and will not splinter, warp, or rot. Over a 20 year lifespan, composite can actually cost less when you factor in the savings on stain, sealant, and labor for annual upkeep.
Frequently asked questions
How many deck boards do I need?
Divide deck width by board width plus gap to get rows. Multiply rows by boards per row (based on deck length and board length). Add 10% waste for cuts and defects.
What gap do I leave between deck boards?
Standard gap is 1/8 inch for pressure treated and wood decking. Composite boards may need 3/16 to 1/4 inch per manufacturer specs. Use a 16d nail or spacer tool for consistent gaps.
How far apart should deck joists be?
16 inches on center is standard for most residential decks. Use 12 inch spacing for composite boards or diagonal patterns. Only use 24 inch spacing with heavy duty lumber and perpendicular board layout.
How many screws do I need per board?
Two screws at every joist crossing. A 12 foot board with 16 inch joist spacing crosses about 9 joists, requiring 18 screws per board. Buy a few extra pounds to account for stripped or broken screws.
How much waste should I plan for?
10% waste is standard for rectangular decks. Add 15% for diagonal patterns, angles, or lower grade lumber with more knots and defects. It is always cheaper to buy extra now than to make a separate trip.