Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Deck boards needed
39
Joists needed
16
Estimated material cost
$1,444
Deck square footage
320
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One click, a permanent link with your numbers baked in.
How to use this
- 1Enter deck length (ft).
- 2Enter deck width (ft).
- 3Enter joist spacing (in).
- 4Enter price per deck board ($).
- 5Enter price per joist ($).
- 6Enter waste factor (%).
- 7Read your deck boards needed on the right — it updates as you type.
- 8Hit Share to keep the scenario or send it to someone.
About this calculator
16x20 is a popular larger deck size, often built to host a full outdoor dining and lounge area. This calculator defaults to those dimensions with 16-inch joist spacing and standard 5.5-inch boards, returning the board count, joist count, and total material cost, all fully editable for your actual layout.
Worked example
Using the values the calculator loads with:
Inputs
- Deck length: 20 ft
- Deck width: 16 ft
- Joist spacing: 16 in
- Price per deck board: 28 $
- Price per joist: 22 $
- Waste factor: 10 %
Results
- Deck boards needed: 39
- Joists needed: 16
- Estimated material cost: $1,444
- Deck square footage: 320
What each field means
Inputs
- Deck length (ft)
- The deck length used in the calculation, measured in ft. Starts at 20 ft so you have a working example on load.
- Deck width (ft)
- The deck width used in the calculation, measured in ft. Starts at 16 ft so you have a working example on load.
- Joist spacing (in)
- The joist spacing used in the calculation, measured in in. Starts at 16 in so you have a working example on load. Accepted range: 12–24 in.
- Price per deck board ($)
- The price per deck board used in the calculation, measured in $. Starts at 28 $ so you have a working example on load.
- Price per joist ($)
- The price per joist used in the calculation, measured in $. Starts at 22 $ so you have a working example on load.
- Waste factor (%)
- The waste factor used in the calculation, measured in %. Starts at 10 % so you have a working example on load. Accepted range: 0–30 %.
Results
- Deck boards needed
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Joists needed
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Estimated material cost
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Deck square footage
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How big is a 16x20 deck in square feet?
320 square feet — large enough for a dining set, lounge area, and grill station, which is why it's one of the most requested deck sizes for full backyard builds.
Do I need a beam in the middle of a 16x20 deck?
Likely yes — spans over roughly 12-14 feet usually require a center beam supported by posts and footings rather than a single joist run, so check your local span tables.
How much lumber cost difference between composite and pressure-treated?
Composite boards typically run 2-3x the price of pressure-treated lumber per board but need no staining or sealing, so adjust the board price field to compare total costs for your material choice.
Accuracy and limitations
- Estimates assume standard, average conditions — local rules, pricing, and materials vary.
- Results are rounded for readability; add a buffer before ordering, booking, or committing.
- Double-check anything with a real cost attached against a local quote.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). 16x20 Deck Material Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/16x20-deck-material-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/16x20-deck-material-calculator" target="_blank" rel="noopener">16x20 Deck Material Calculator — RevenueLab</a> (2026).</p>
Source: [16x20 Deck Material Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/16x20-deck-material-calculator) (2026).