Decking Calculator

Free

Decking · Boards, joists, beams and posts · default waste 10%

Enter your measurements

Numbers start at typical defaults — change anything. Every result states the inputs and assumptions used.

Deck length(ft)

Deck width(ft)

Board width(in)

A nominal 2 × 6 deck board is 5.5 in wide.

Board gap(in)

Joist spacing

Beam lines

Post spacing(ft)

Post height above grade(ft)

Stair steps (risers)

Stair width(ft)

Waste factor(%)

Applied once to each material quantity, then rounded up to the orderable increment.

Product assumptions — editable8

Sheet sizes, coverage rates, bundle counts, bag yield and similar come from the product you are buying. Change any of them to match your supplier — whatever you set is shown again with the result.

Deck board stock length(ft)

Joist stock length(ft)

Beam stock length(ft)

Plies per beam

Post stock length(ft)

Deck screws per sq ft

Concrete bags per post(bags)

Two 60 lb bags per post is a common allowance in normal soil.

Stringer length per riser(ft)

Enter your measurements and press "Calculate materials" to see the calculated quantity, waste-adjusted quantity and recommended order quantity.

What this calculator does

•Deck area = length × width
•Board coverage = (board width + gap) ÷ 12 ft; board linear ft = deck area ÷ board coverage
•Boards = board linear ft ÷ board stock length
•Joists = ⌈(width × 12) ÷ joist spacing⌉ + 1, each cut from joist stock for the deck length
•Beam linear ft = beam lines × plies × deck length
•Posts per beam line = ⌈deck length ÷ post spacing⌉ + 1; post pieces = posts × height ÷ post stock
•Stairs: treads = steps × stair width; stringers = 2 per 4 ft of width × steps × stringer length per riser
•Deck screws = deck area × screws per sq ft; joist hangers = 2 per joist

Deterministic by design: no AI, no lookups, no network calls — the same inputs always give the same numbers. Product values such as coverage rates and bundle counts are editable and shown with the result.