Deck Calculator for a 16×20 Deck
Estimate materials for a 16×20 ft deck.
A 16×20 ft deck (320 sq ft) fits a full dining table, lounge seating and a grill area. Joists on 16 in centers with a 2×10 rim board, and 16 or 20 ft composite deck boards run the long way to minimize butt joints. Plan on 8 ft footings if the deck attaches to the house.
Deck boards
35
Joists
13
Screws
280
192 ft² deck
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How does the deck calculator work?
Board count = (deck length ÷ board length) × (deck width in inches ÷ board actual width). A "5/4×6" board is really 5.5 in wide. Joists at 16 in on-center: (length in inches ÷ 16) + 1.
Which guide explains this in more depth?
- Riser-and-tread math plus 2026 material prices for a full stair build. Read the stair calculator cost breakdown guide for the full worked example.
What else do people ask about this calculator?
How many boards for a 16×20 deck?
20 ft boards perpendicular to 16 ft joists: ~38 boards. Add 10% waste — call it 42 boards, plus 5 more for picture-frame trim.
What joist size for a 16 ft deck span?
2×10 pressure-treated joists at 16 in on center for a 16 ft span. Add a mid-span beam to break the joist run if you want to size down to 2×8.
How many deck boards for a 16×12 deck?
At 12 ft boards and 5.5 in actual width, about 27 boards plus 10% waste — order 30.
How far apart should deck joists be?
16 in on-center for standard decking; 12 in for composite or for spans over 12 ft.
Which related calculators should I use next?
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