Decking Calculator
Calculate decking accurately for your build. Get material quantities, waste allowances, and project cost breakdowns. Get results you can export or share.
Reviewed by Abdullah, Technical Content Specialist
Formula
Boards = ceil(Width / Board Width) x ceil(Length / Board Length) x (1 + Waste%)
Divide the deck width by the effective board width (including gap) to get rows, and the deck length by board length to get boards per row. Multiply for total count, then add the waste percentage for cuts and defects.
Worked Examples
Example 1: Standard Backyard Deck
Problem:Calculate decking for a 20 x 12 foot deck using 5.5" x 12 ft boards with 10% waste.
Solution:Deck area = 20 x 12 = 240 sq ft\nBoards across = ceil(12 / (5.625/12)) = 26 rows\nBoards per row = ceil(20 / 12) = 2 boards\nBase count = 26 x 2 = 52 boards\nWith 10% waste = ceil(52 x 1.10) = 58 boards
Result:58 boards for 240 sq ft deck
Example 2: Small Porch Deck
Problem:Calculate for an 8 x 10 foot porch using 5.5" x 8 ft boards with 10% waste.
Solution:Deck area = 80 sq ft\nBoards across = ceil(10 / 0.469) = 22 rows\nBoards per row = ceil(8 / 8) = 1 board\nBase count = 22 boards\nWith waste = ceil(22 x 1.10) = 25 boards
Result:25 boards for 80 sq ft porch
Frequently Asked Questions
How much waste should I add for decking materials?
For a standard rectangular deck, add 10% waste factor to your board count. For decks with angles, curves, or complex shapes, increase the waste factor to 15-20%. Diagonal decking patterns require 15% extra material compared to perpendicular layouts. Picture-frame borders and herringbone patterns can push waste to 20-25%. Shorter board lengths generally produce less waste since offcuts can be reused. Always round up your board count and consider buying a few extra boards to have matching replacements on hand.
What are the best decking materials for longevity?
Pressure-treated pine is the most affordable option at $2-4 per linear foot with a 15-20 year lifespan, but requires annual sealing. Cedar and redwood cost $4-8 per linear foot and naturally resist rot for 15-25 years. Composite decking from brands like Trex or TimberTech costs $6-12 per linear foot but lasts 25-50 years with minimal maintenance. PVC decking at $8-15 per linear foot offers the best moisture resistance. Ipe hardwood is the premium option at $10-20 per linear foot, lasting 40-75 years with exceptional hardness and beauty.
How many screws do I need for decking?
Plan for approximately 2 to 2.5 screws per square foot of decking when using face-fastening methods. For a standard 5.5-inch wide board on 16-inch center joists, you need 2 screws at each joist crossing, which works out to about 350 screws per 100 square feet. Hidden fastening systems use clips at each joist intersection, typically requiring one clip per joist per board. Use stainless steel or coated deck screws rated for your material type to prevent corrosion and staining.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy