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How much decking does this rectangular layout need?

Enter approved rectangular deck dimensions, the selected product's actual face width, and the required installed gap. The result covers field rows, not structural design or a cut plan.

A 12 × 10 ft field using a 5.5 in board face and a 0.125 in gap needs 22 rows and 264 linear ft before any user-entered waste allowance.

Deck board layout calculator

Turn approved rectangular deck dimensions into field-board rows and total board-run length.

Length follows each board row. Width is measured across the rows. Use dimensions from the approved plan or verified site layout.

Use the selected product's actual face width and the gap required by the approved installation detail. Do not use the nominal lumber name as the face width.

22 rows · 264 linear ft

80.47 linear m before any extra material.

Rows = ceiling((120 in + 0.125 in gap) ÷ 5.625 in pitch) = 22; total run = 22 × 12 ft.

This field-layout result does not select stock lengths, cuts, borders, stairs, spans, framing, footings, guards, ledgers, or fasteners.

View project plan

Calculate once to save this result.

See the formula and scope

Rows = ceiling((deck width + required gap) ÷ (actual board face width + required gap)). Adding the gap once to the numerator accounts for gaps only between boards, not after the final board. Total board run = rows × deck length. Extra material, if entered, is applied only after the base run. Calculate borders, picture frames, stairs, angled layouts, breaks, and different run lengths separately.

Your next step

Use your result to check what comes next before you head to the store.

The visible formula

Row count = ceiling((deck width + required gap) ÷ (actual board face width + required gap)). The numerator adds one gap so the layout counts gaps between boards without assuming another gap after the final row. Base linear run = row count × deck length. If you enter a waste allowance, it is applied to the base linear run after those two steps.

What belongs in a separate run

The rectangular result assumes every field row follows the entered deck length. Borders, picture frames, stairs, angled boards, openings, direction changes, breaks, butt joints, and sections with a different run length need their own measured takeoff. This calculator does not turn linear length into a stock-board count because available lengths and the approved cut layout are project-specific.

This calculator does not design a deck

Use dimensions, orientation, and gap requirements from the applicable approved plan, code information, and product instructions. The calculator does not establish joist or beam spans, loads, footings, guards, stairs, ledger details, drainage, board fastening, connector compatibility, or permits. Stop and consult the building authority or a qualified professional when those details are not already established.

Why the sources do not supply a universal gap or waste rate

The USDA Wood Handbook covers wood moisture, durability, fasteners, and construction fundamentals. It does not replace a site-specific deck design or the selected decking manufacturer's installation instructions. The conversion source supports the exact U.S.-metric arithmetic. Neither source supplies a universal gap, structural span, fastener schedule, or waste percentage.

Sources and notes

Source links reviewed July 16, 2026. A review date is not the document's publication date.

  1. USDA Forest Products Laboratory: Wood Handbook: Wood as an Engineering MaterialUnited States · government guide

    Structural deck design remains subject to local code and site-specific engineering requirements.

  2. National Institute of Standards and Technology: NIST Guide to the SI, Appendix B — Conversion FactorsUnited States · government standard

    Code retains exact defining constants where NIST identifies an exact relationship.