deck calculator

Deck Calculator – Estimate Boards and Lumber for Your Deck Instantly

This Deck Calculator helps you estimate the number of deck boards, total board length, and deck area required for your project. Whether you're building a backyard deck, patio platform, porch expansion, or outdoor entertainment space, this tool lets you plan your materials with accuracy and ease.

By entering the deck dimensions, board size, spacing, and waste allowance, the calculator instantly shows:

• Deck area (square feet)
• Number of boards required
• Total linear feet of lumber
• Waste-adjusted board count

This eliminates guesswork, prevents over-buying, and ensures your deck project starts with the right amount of material.

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How the Deck Calculator Works

The calculator uses standard deck-building formulas based on:

1. Deck Area Formula

$$\text{Deck Area (sq ft)} = \text{Length (ft)} \times \text{Width (ft)}$$Deck Area (sq ft)=Length (ft)×Width (ft)

2. Coverage of Each Board

Boards run along the deck length, while spacing is applied across the width.

Coverage per board (in inches):$$\text{Board Coverage} = \text{Board Width} + \text{Spacing}$$Board Coverage=Board Width+Spacing

3. Number of Boards Across

$$\text{Boards Across} = \left\lceil \frac{\text{Deck Width (inches)}}{\text{Board Coverage}} \right\rceil$$Boards Across=⌈Board CoverageDeck Width (inches)​⌉

4. Number of Boards Along Length

$$\text{Boards Along} = \left\lceil \frac{\text{Deck Length}}{\text{Board Length}} \right\rceil$$Boards Along=⌈Board LengthDeck Length​⌉

5. Total Boards Needed

$$\text{Total Boards} = \text{Boards Across} \times \text{Boards Along}$$Total Boards=Boards Across×Boards Along

6. Waste Adjustment

$$\text{Total With Waste} = \text{Total Boards} \times \left(1 + \frac{\text{Waste \%}}{100}\right)$$Total With Waste=Total Boards×(1+100Waste %​)

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How to Use the Deck Calculator

1. Enter the deck length

This is the long side of your deck (in feet).

2. Enter the deck width

This is the side running perpendicular to the boards (in feet).

3. Enter board length

Common board lengths: 8 ft, 10 ft, 12 ft, 16 ft.

4. Enter board width (in inches)

For example: standard 5.5" deck boards.

5. Enter gap between boards

Typical spacing is 0.125" to 0.25".

6. Enter waste percentage

Most projects use 5–15% waste.

7. Click “Calculate”

The output shows:

• Total deck area
• Number of boards needed
• Total linear feet of decking required

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Example Deck Calculations

✔ Example 1: 20 ft × 12 ft deck

Board width: 5.5"
Spacing: 0.25"
Board length: 12 ft
Waste: 10%

Deck area:$$20 \times 12 = 240 \text{ sq ft}$$20×12=240 sq ft

Boards across:$$12 \text{ ft} = 144 \text{ in} \text{Coverage per board} = 5.5 + 0.25 = 5.75 \text{ in} \Rightarrow 144 / 5.75 = 25.04 \approx 26 \text{ boards across}$$12 ft=144 inCoverage per board=5.5+0.25=5.75 in⇒144/5.75=25.04≈26 boards across

Boards along:$$20 / 12 = 1.67 \approx 2$$20/12=1.67≈2

Total raw boards:$$26 \times 2 = 52$$26×2=52

With 10% waste:$$52 \times 1.1 = 57.2 \approx 57 \text{ boards}$$52×1.1=57.2≈57 boards

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✔ Example 2: 16 ft × 10 ft deck

Board width: 6"
Spacing: 0.2"
Board length: 8 ft
Waste: 15%

Deck area:$$16 \times 10 = 160 \text{ sq ft}$$16×10=160 sq ft

Total boards needed (after waste): 49 boards

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Why Use This Deck Calculator?

Perfect for:

• DIY deck builders
• Contractors
• Home renovation projects
• Material budgeting
• Estimating lumber needs accurately
• Choosing between deck board sizes

Benefits:

✔ Accurate lumber estimation
✔ Prevents under-buying or over-buying
✔ Supports different board sizes and spacing
✔ Includes waste allowance
✔ Helps plan budget and supplies
✔ Mobile-friendly and easy to use

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Frequently Asked Questions (FAQ)

1. How much waste should I include in my deck material estimate?

Most builders use 5–15% waste to account for cuts, defects, and misalignment.

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2. What size boards are most common for decking?

Common sizes include:

• 5.5” × 12 ft
• 5.5” × 16 ft
• 6” × 12 ft

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3. Does this calculator handle angled or curved decks?

This version works for rectangular decks, but I can create:

• Angled deck calculator
• Multi-section deck calculator

Just ask!

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4. Can I use metric measurements?

This tool uses feet and inches, but I can generate a metric deck calculator as well.

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5. Does board spacing matter?

Yes. Proper spacing prevents moisture buildup and allows expansion.

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6. Can this help me estimate deck cost?

Indirectly, yes—once you know the number of boards, you can multiply by price per board.