Deck Calculator

Divide deck width by board width plus gap to get the number of rows, then multiply by stock boards per row (deck length divided by stock board length, rounded up). A 16 by 12 ft deck with 5.5 in boards and 12 ft stock needs about 52 boards. This is a straight-layout quantity estimate; confirm board orientation, pattern, allowable spans, fastening, and waste with the decking manufacturer.

Use the joist spacing in the decking manufacturer's span table and the approved deck plan. The calculator can estimate 12, 16, or 24 in on-center layouts but does not determine a safe span, joist size, beam layout, connection, footing, or ledger detail. Have a qualified deck professional verify a real structure.

The calculator models two beams, or three above 16 ft wide, and one 50 lb bag per post as material estimates. That is not a footing, beam, post, or connection design. Frost depth, soil bearing, uplift, loads, spans, and local requirements can change every input. Use an approved plan or qualified deck professional.

The calculator treats railing as perimeter minus attached sides and uses a 6 ft post-spacing estimate. Railing height, opening limits, post strength, fasteners, stairs, and local code need a project-specific design. Verify them before building.

The calculator uses 3 lb of #8 by 2.5 in screws per 100 sq ft as a purchasing allowance. Select screw type, length, spacing, corrosion resistance, and approved fasteners from the board and framing manufacturer's instructions.