Free Deck Calculator
Estimate deck boards, joists and screws from your deck size and board width. Free, fast, and works entirely in your browser with no sign-up required.
Updated
Decking materials
A board sold as "6 inch" measures 5.5 in.
Extra material for cuts, spillage and breakage.
Deck boards needed
39
boards
- Deck area
- 192ft²
- Joists
- 13joists
- Screws (approx.)
- 1,014screws
How this is calculated
boards = area ÷ (board width ÷ 12 × board length), plus waste; joists = length × 12 ÷ spacing + 1
- Board width is the ACTUAL width — nominal "6 inch" decking measures 5.5 in, which is the default.
- Two screws per board at every joist crossing.
- Joist count assumes a simple rectangular frame; stairs, railings and beams are not included.
- Composite and hardwood boards vary — check the actual width before ordering.
Frequently Asked Questions
How does the Deck Calculator work?
It applies the formula boards = area ÷ (board width ÷ 12 × board length), plus waste; joists = length × 12 ÷ spacing + 1. Enter your measurements and the result updates instantly in your browser — nothing is uploaded and no sign-up is needed.
Why should I include a waste allowance?
Offcuts, spillage, breakage and an uneven sub-base all consume material that the raw geometry does not account for. The default allowance is deliberately modest; increase it for complex layouts, and remember that running short usually costs more in a second delivery than the surplus did.
Are the results exact?
They are a close estimate, not a guarantee. Board width is the ACTUAL width — nominal "6 inch" decking measures 5.5 in, which is the default. Real materials vary by supplier, moisture content and compaction, so confirm the rate with your supplier before placing a large order.
Is this tool free?
Yes, completely free with no registration. All calculations happen client-side in your browser.
Does it work on mobile?
Yes. The calculator is fully responsive and works on phones and tablets in any modern browser — useful when you are measuring on site.
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About the Deck Calculator
The Deck Calculator converts a deck footprint into the number of boards, joists and screws you need, using the actual board width rather than the nominal one. Enter your measurements and the result updates as you type — there is nothing to submit and nothing to wait for.
Everything runs in your browser. Nothing you enter is sent to a server, there is no sign-up, and there is no usage limit.
Who it's for
Anyone building or re-decking, and suppliers assembling a materials list.
How the calculation works
boards = area ÷ (board width ÷ 12 × board length), plus waste; joists = length × 12 ÷ spacing + 1
The result depends on a few standard constants, which are stated on the page rather than hidden:
- Board width is the ACTUAL width — nominal "6 inch" decking measures 5.5 in, which is the default.
- Two screws per board at every joist crossing.
- Joist count assumes a simple rectangular frame; stairs, railings and beams are not included.
- Composite and hardwood boards vary — check the actual width before ordering.
Getting an accurate estimate
Measure twice. Small errors in a linear dimension compound, because material volume scales with two or three of them at once — a 6-inch error across a 20-foot run is over a cubic foot of material on a 4-inch pour.
Keep the waste allowance. The default is deliberately conservative: offcuts, spillage, uneven sub-base and breakage are all real, and running short mid-job usually costs more in a second delivery than the surplus did.
Round up when you order. Suppliers sell in fixed increments — quarter yards, whole bags, full boxes — so treat the figure here as the minimum you need rather than the exact amount to buy.