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BuildMate
Outdoor

Deck Calculator Calculator USA 2026

Estimate deck boards, joists and screws for pressure-treated or composite decking.

Unit system

Enter your measurements

Results

Deck area

320 sq ft

Decking boards

64

Joists (16" O.C.)

13

Deck screws

1280

Calculation steps
  1. 1.Deck area = 20 × 16 = 320 sq ft
  2. 2.Board coverage = (5.5 ÷ 12) × 12 = 5.50 sq ft
  3. 3.Boards = ⌈(320 ÷ 5.50) × 1.10⌉ = 64
  4. 4.Joists = ⌈(16 × 12) ÷ 16⌉ + 1 = 13

Includes a standard waste allowance. Verify with your supplier before ordering.

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Disclaimer: Estimates based on 2026 RSMeans USA data. Actual quantities vary by site conditions, waste and installer practices. Verify with your supplier or contractor before ordering.

How it works

  1. 1Enter deck length and width in feet.
  2. 2Pick a board width (5.5" standard).
  3. 3We add 10% for cuts and estimate joists at 16" on center.

Formula

Boards = Area ÷ (Board Width × Board Length) × 1.10

Worked example

16×20 ft deck = 320 sq ft. Using 5.5"×12 ft boards ≈ 70 boards.

Frequently asked questions

Joist spacing?

16" O.C. is standard; 12" for diagonal decking.