Decking Calculators

How decking estimating works

Deck boards are sold in fixed lengths — typically 12, 16 and 20 ft in North America and 3.6, 4.8 and 5.4 m elsewhere — and in nominal widths that are smaller in reality: a "6-inch" board is about 5½ in (140 mm) wide. The number of rows you need comes from the deck width divided by the actual board width plus the gap the manufacturer specifies; the number of boards then depends on how well the stock length matches the deck length.

Joist count and fasteners follow from the joist spacing. Two screws per board at every joist is the usual face-fixing rule; hidden clip systems use one clip per crossing. Framing size and span, ledgers and footings are structural and must follow local code — see the American Wood Council DCA 6 guide in the US or your local building authority elsewhere.

Glossary

On centre (o.c.)

spacing measured centre to centre

Ledger

board that attaches the deck to the house

Picture frame

border boards around the deck edge

Composite decking

wood-plastic or capped polymer boards

Updated 2026-10-18 by the DIYCalcLab Editorial Team · How we calculate