Decking Calculator
Calculate exactly how many deck boards, linear feet, and screws you need for your project.
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Enter your deck dimensions or total square footage to calculate materials needed.
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Try it freeDecking Calculator: Figure Out How Many Boards You Need
Planning a deck project? This free decking calculator helps you estimate exactly how many boards, linear feet, and screws you'll need. Whether you're building a simple backyard deck or a multi-level outdoor living space, get accurate material estimates in seconds.
From Invoice Mama's collection of free contractor tools, this calculator takes the guesswork out of deck material planning. Enter your deck dimensions in feet or meters, choose your board size, and we'll handle the math—including waste factor and hardware estimates. Works great for both imperial and metric users.
How to Calculate Deck Boards Needed
Understanding the math behind deck material estimates helps you plan smarter and avoid costly mistakes.
Calculating decking materials isn't as simple as dividing square footage by board size. You need to account for actual board dimensions (not nominal), gap spacing between boards, installation angle, and waste from cuts.
- 1
Calculate Your Deck Area
Multiply length × width in feet or meters. For a 12×20 ft deck, thats 240 sq ft. In metric: 3.6m × 6m = 21.6 m². Irregular shapes? Break it into rectangles and add them up.
- 2
Determine Board Coverage
Each board covers: actual width × length. A 5/4×6 board at 12 feet covers about 5.5 sq ft (factoring in the gap between boards).
- 3
Add Waste Factor
Multiply by 1.05 for 5% waste (perpendicular 90° install) or 1.10 for 10% (diagonal 45° install). This accounts for cuts and unusable pieces.
- 4
Round Up
Always round up to the next whole number. You can't buy half a board, and having extras is better than falling short.
The Deck Board Formula
Here is the basic formula for calculating deck boards
Example: A 240 sq ft deck (22 m²) using 5/4×6 boards (140mm actual width) at 12 feet (3.6m) long with 10% waste: (240 ÷ 5.5) × 1.10 = 48 boards needed.
Deck Board Sizes: Nominal vs Actual Dimensions
Lumber sizes can be confusing. Here is what those numbers actually mean.
When you buy a "2×6" board, you are not getting 2 inches by 6 inches. Nominal sizes refer to the rough-cut dimensions before planing. The actual dimensions are smaller—and these are what matter for your calculations.
Nominal Size | Actual Size | Best For |
|---|---|---|
| 5/4 × 4 | 1" × 3.5" | Narrow accent boards, smaller decks |
| 5/4 × 6 | 1" × 5.5" | Most residential decks (most popular) |
| 2 × 4 | 1.5" × 3.5" | Heavy-duty applications, railings |
| 2 × 6 | 1.5" × 5.5" | Commercial or high-traffic areas |
Pro tip: 5/4 deck boards are specifically designed for decking. They are thick enough to span standard joist spacing but lighter and more affordable than 2× lumber.
Choosing the Right Board Length
Pick lengths that minimize waste and seams
Standard deck board lengths are 8, 10, 12, 16, and 20 feet (2.4m, 3m, 3.6m, 4.9m, and 6m). The right choice depends on your deck dimensions and how you want seams to fall.
- 12-foot boards (3.6m)Most popular length. Easy to transport and handle. Works well for decks up to 12 feet (3.6m) wide.
- 16-foot boards (4.9m)Great for wider decks. Fewer seams mean a cleaner look but harder to transport in a standard pickup.
- 20-foot boards (6m)Best for large decks. Typically special order. Minimizes waste on long runs.
- Mixing lengthsYou can combine lengths strategically to reduce waste. Just make sure seams are staggered and fall over joists.
Deck Board Installation Patterns
Your choice of pattern affects both appearance and material needs
Pattern | Extra Material Typical waste | Joist Spacing Required spacing | Best For Recommended use |
|---|---|---|---|
| Perpendicular (90°) | +5% waste | 16" (400mm) on center | Most decks, easiest install |
| Diagonal (45°) | +10% waste | 12" (300mm) on center | Visual interest, square decks |
| Herringbone | +15-20% waste | 12" (300mm) on center | Premium look, experienced DIYers |
| Picture Frame | +5-10% extra | 16" (400mm) on center | Finished edge, professional look |
Diagonal installation looks stunning but requires more materials and closer joist spacing. Make sure your frame is built to handle the chosen pattern before ordering materials.
Deck Board Gap Spacing Guide
Proper spacing ensures drainage and prevents warping
The gap between deck boards isn't just aesthetic—it's functional. Proper spacing allows water to drain, debris to fall through, and wood to expand and contract with temperature changes.
- 1/8" gap (3mm): Tight spacing, good for composite boards that don't shrink
- 3/16" gap (5mm): Standard for most installations, recommended for pressure-treated
- 1/4" gap (6mm): Wider spacing, helps in wet climates or with dry lumber
- Butt joints: No gap needed at board ends over joists
If you're using wet pressure-treated lumber, you can install boards touching each other. They'll shrink as they dry, naturally creating the gap. Kiln-dried lumber should be gapped at installation.
Decking Material Options
Choose the right material for your budget and lifestyle
Material | Cost Range | Lifespan | Maintenance |
|---|---|---|---|
| Pressure-Treated Pine | $2-4/sq ft | 10-15 years | Annual sealing, staining |
| Cedar | $4-8/sq ft | 15-20 years | Periodic sealing optional |
| Composite | $8-15/sq ft | 25-30 years | Minimal, occasional cleaning |
| PVC | $10-18/sq ft | 30+ years | Very low, no sealing |
| Tropical Hardwood (Ipe) | $15-25/sq ft | 40+ years | Oil annually for color |
While pressure-treated lumber has the lowest upfront cost, composite and PVC decking often provide better value over time when you factor in maintenance savings and longer lifespan.
Understanding Waste Factor
Why you should always order more than the calculator's base number
Waste factor accounts for the material you'll lose to cuts, defects, and mistakes. Even experienced deck builders factor in extra material—running short mid-project costs more than buying a few extra boards upfront.
- 5% Waste (90° Standard)Standard for perpendicular installation on rectangular decks. The default for straight board patterns.
- 10% Waste (45° Standard)Standard for diagonal (45°) patterns. Accounts for angled cuts at deck edges.
- 15% WasteComplex shapes, multiple angles, or decks with obstacles requiring extra cuts.
- 20%+ WasteIntricate patterns like herringbone, curves, or irregular deck shapes.
Common Deck Planning Mistakes to Avoid
Learn from others so you don't make these costly errors
- Using Nominal DimensionsA 2×6 is actually 1.5" × 5.5". Using nominal sizes in calculations means you'll come up short on materials.
- Forgetting Gap SpacingThe 3/16" gap between each board adds up. Over 20 boards, that's almost 4 inches of width you need to account for.
- Ignoring Board DefectsLumber yards have return policies for defective boards. Inspect before installing, and factor in replacements.
- Not Planning for SeamsBoard ends must fall on joists. Poor planning means more cutting and waste.
Tips for Saving Money on Deck Materials
Smart planning stretches your budget further
- Design your deck in standard lumber increments (8, 12, 16 feet / 2.4, 3.6, 4.9 meters) to minimize cuts
- Buy materials in bulk—most yards offer discounts for larger orders
- Check for contractor pricing or ask about scratch-and-dent deals
- Consider mixing materials: composite for the surface, pressure-treated for framing
- Time your purchase—lumber prices often drop in late fall and winter
- Return unused materials promptly (keep receipts and don't open shrink wrap)
Hardware and Fastener Estimates
Don't forget the screws, nails, and hidden fasteners
Deck screws are sold by the pound or box. Here's how to estimate what you need:
- Standard screw method: 2 screws per board at each joist crossing
- Hidden fasteners: Approximately half the screw count (e.g., 435 fasteners for 870 screws)
- 2.5" or 3" deck screws work for most applications
- Stainless steel or coated screws prevent rust stains on your deck
A typical 5-lb box (2.2kg) contains roughly 350 deck screws. For a 200 sq ft deck with 12" joist spacing at 90°, you'll need approximately 870 screws—so grab three boxes. At 16" spacing, you'll need about 650 screws (two boxes).
From Calculation to Invoice
Turn your deck estimate into professional project documentation
Once you've calculated your materials, the next step is creating a professional estimate or invoice for the project. Whether you're a contractor bidding on a job or a homeowner tracking costs, proper documentation saves headaches later.
Invoice Mama helps contractors create professional estimates and invoices in seconds. Our AI-powered system can turn your material calculations into polished documents that help you win jobs and get paid faster. Try it free and see why deck builders love our simple approach to paperwork.
Frequently Asked Questions
Quick answers to common decking calculation questions
How many deck boards do I need for my project?
The number of deck boards depends on your deck size, board dimensions, and installation angle. For a standard 12x20 ft deck (3.6m × 6m, or about 22 m²) using 5/4" × 6" boards at 12 feet long, you will need approximately 38-40 boards with 5% waste for 90° installation. Our calculator factors in board width, length, joist spacing, and recommended waste percentage for accurate results.
What is the most common deck board size?
5/4" × 6" is the most popular deck board size for residential projects. The "5/4" means the board is 1.25 inches thick (actual), while the width is 5.5 inches (actual). This size offers a good balance between durability, cost, and appearance. For heavier traffic areas, 2" × 6" boards provide extra strength.
How do I calculate square footage or square meters for a deck?
Multiply your deck length by its width to get the area. For example, a 20 ft × 12 ft deck equals 240 square feet (or 6m × 3.6m = 22 square meters). For irregular shapes, divide the deck into rectangles, calculate each section, and add them together. Our calculator supports both imperial (feet) and metric (meters) units.
What board length should I choose for my deck?
Choose board lengths that minimize waste and reduce the number of cuts needed. Common lengths are 8, 10, 12, 16, and 20 feet. If your deck is 12 feet wide, using 12-foot boards means fewer cuts. For a 14-foot deck, 16-foot boards will work better then 12-foot boards that would require splicing.
How much extra material should I order for waste?
Plan for 5% extra material for standard rectangular decks with perpendicular (90°) board installation. For diagonal (45-degree) patterns, add 10% waste. Complex designs with curves, multiple angles, or intricate patterns may require 15-20% or more. Its better to have extra boards than to run short mid-project.
What gap should I leave between deck boards?
Standard gap spacing is 3/16" (about 5mm) between deck boards. This allows for water drainage and wood expansion. Composite decking typically uses 1/8" to 1/4" gaps (3-6mm). For pressure-treated wood that is still wet, you can install boards touching since they will shrink as they dry.
How many screws do I need for decking?
Screw count depends on board angle and joist spacing. For a 200 sq ft deck with 12" on-center joists: perpendicular (90°) installation needs about 870 screws, while diagonal (45°) needs about 620 screws. At 16" on-center spacing, reduce these by 25%. Each board typically needs 2 screws at every joist intersection. Use stainless steel or coated deck screws designed for outdoor use.
Should I install deck boards at 90 degrees or 45 degrees?
Perpendicular (90-degree) installation is more common and uses less material with only 5% waste factor. Diagonal (45-degree) patterns create visual interest but require 10% waste factor due to angled cuts. Diagonal installation also needs closer joist spacing (12" vs 16" on center) for proper support and uses fewer screws per linear foot.
What is the difference between nominal and actual board size?
Nominal size is the name (like 2×6), while actual size is the real measurement after milling. A 2×6 board actually measures 1.5" × 5.5". A 5/4×6 deck board is actually 1" × 5.5". Always use actual dimensions when calculating materials to ensure accurate coverage estimates.
How do I calculate linear feet of decking needed?
Linear feet equals the total number of boards multiplied by their length. For example, 40 boards at 12 feet each equals 480 linear feet (146 linear meters). This measurement helps when comparing prices or ordering materials since lumber is often sold by linear foot.
Can I use this calculator with metric measurements?
Yes! Our decking calculator supports both imperial (feet) and metric (meters) units. Simply toggle between ft and m at the top of the calculator. Enter your deck dimensions in meters, and results will show linear meters alongside the board count. Common conversions: 1 foot = 0.3048 meters, 1 square foot = 0.093 square meters.
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Ready to Build Your Dream Deck?
Accurate material estimates are the foundation of a successful project
Whether you're a DIY weekend warrior or a professional deck contractor, getting your material estimate right saves time, money, and frustration. Use this calculator whenever you're planning a deck project, and don't forget to factor in waste, hardware, and a few extra boards just in case.
Happy building!
Deck Builders: Streamline Your Paperwork
Invoice Mama helps deck contractors create professional estimates and invoices in seconds. Turn your material calculations into polished documents that win jobs and get you paid faster.