Free Deck Calculator – Board Count & Linear Feet

Deck Board & Linear Feet Calculator Guide

The Deck Calculator estimates how many decking boards and total linear feet you need to surface a deck frame. Begin by measuring the deck you intend to cover: the length and the width in feet, noting which direction the boards will actually run versus the direction they span. Then choose your board profile. Most decking comes in nominal 4-inch or 6-inch face widths (actual faces are closer to 3.5 and 5.5 inches) and in stock lengths of 8, 10, 12, or 16 feet. Finally set the gap you will leave between boards for drainage and seasonal movement, commonly 1/8 inch (0.125 in) for kiln-dried wood and up to 1/4 inch for wet-treated or composite material. This tool sizes surface boards only; it does not calculate joists, beams, posts, fasteners, or railing. Measure the framed footprint, not lumber on hand, and round each dimension up to the nearest inch so partial rows are never under-counted.

Method: effective board coverage equals (face width + gap) converted to feet. Rows across the deck = deck width / effective coverage, rounded up. Boards per row = deck length / board stock length, rounded up. Multiply rows by boards per row, then add a 10% waste allowance. Worked example: a 12 ft x 16 ft deck (3.7 m x 4.9 m) with 6-inch boards (5.5 in face) and a 1/8 in gap gives an effective coverage of (5.5 + 0.125)/12 = 0.469 ft per board. Rows across the 12 ft width = 12 / 0.469 = 25.6, rounded to 26 rows. Using 16 ft boards along the 16 ft length, each row needs 1 board, so 26 x 1 = 26 boards. Add 10% waste: 26 x 1.10 = 28.6, rounded to 29 boards. Total linear feet = 29 x 16 = 464 linear feet of decking to purchase.

Waste of 10% covers end trims, cull boards, and the offcuts created by staggering joints; bump this to 15% for diagonal or herringbone patterns, which force angled cuts on every board. The single most common mistake is ignoring the gap, which under-orders boards by 2-4% on wide decks. A second error is assuming boards run lengthwise when the deck is framed for the boards to span the short direction; confirm your joist direction first, since deck boards must run perpendicular to joists. For structural spacing, the International Residential Code (IRC R507) governs joist spans and ledger attachment, and most 5/4 and 2x decking is rated for joists at 16 inches on center, with some products requiring 12 inches for diagonal layouts. Buy all boards from one production lot for color consistency, and keep a few spares for future repairs. Wet-treated lumber shrinks as it dries, so a tighter installed gap will naturally widen, which is why 1/8 inch is the typical starting point.