Decking Calculator
Estimate deck boards, board rows, boards per row, purchased board length, waste allowance, deck area, and optional material cost.
Results
This estimate is for a simple rectangular deck surface. Real decking needs can vary because of breaker boards, borders, picture-frame edges, diagonal layouts, stairs, damaged boards, butt-joint layout, joist spacing, board overhang, and manufacturer board dimensions.
Use this Decking Calculator to estimate the number of boards and optional material cost for a simple rectangular deck. Enter the deck dimensions, board size, board gap, board direction, and waste allowance.
Decking Calculation Method
Deck area = deck length × deck width
Effective board width = board width + board gap
Board rows = deck span ÷ effective board width
Boards per row = board run length ÷ board length
Base boards = board rows × boards per row
Total boards = base boards × (1 + waste percentage ÷ 100)
Board rows, boards per row, and the final board quantity are rounded up to whole boards.
When a price is entered:
Estimated cost = total boards × price per board
Example
Suppose a deck is 16 ft long and 12 ft wide. The boards are 5.5 inches wide, 12 ft long, and installed with a 0.25-inch gap along the deck length. A 10% waste allowance is included.
Effective board width = (5.5 + 0.25) ÷ 12 = 0.479 ft
Board rows = 12 ÷ 0.479 = 25.05
Round up to 26 rows.
Boards per row = 16 ÷ 12 = 1.34
Round up to 2 boards per row.
Base boards = 26 × 2 = 52 boards
Total boards = 52 × 1.10 = 57.2
Round up to approximately 58 deck boards.
Important Notes
- Use the actual board dimensions and spacing required by the manufacturer.
- Board direction affects the number of rows and boards required per row.
- Picture-frame borders, diagonal patterns, stairs, fascia, breaker boards, damaged boards, and unusable offcuts may require additional material.
- The calculator does not estimate joists, beams, posts, footings, fasteners, railings, structural design, delivery, or labour.