🪵 Decking Calculator

Calculate materials, cost, and boards needed for your decking project

📐 Deck Shape:

📏 Dimensions:

Length (m)

Width (m)

📏 L-Shape Dimensions:

Section A Length

Section A Width

Section B Length

Section B Width

🪵 Board Size:

📏 Board Spacing:

3mm 5mm 8mm

🏷️ Material Type:

⚠️ Wastage Allowance:

Recommended: 10-15% for cuts & waste

📊

Total Area

m²

🪵

Boards Needed

boards (with waste)

📏

Linear Meters

0 m

💰

Material Cost

£0

🔩

Screws Needed

🪚

Waste Added

0 m²

🏗️

Joists Needed

0 pcs

💰

Total Cost Est.

£0

💡 Pro Tips

Based on your deck size, we recommend ordering 10-15% extra boards for cuts.

⚠️ Important

Always check local building regulations. Add 10-15% for cuts and waste. Prices are estimates only.

Decking Calculator 2026 | Wood & Composite Material Estimator

Free DIY Tool - 2026 Updated

Decking Calculator: Wood, Composite & WPC Material Estimator

Calculate boards, joists, screws, concrete footings, and total cost for your decking project. Perfect for DIY enthusiasts, contractors, and homeowners planning a new deck.

Used by 100k+ DIYers 4.9 out of 5 Rating 100% Free Tool Instant Results

Types of Decking Materials (2026 Guide)

🌲

Pressure Treated Wood

£30-£50 / $40-65 per m²

Traditional, affordable, natural look

🏭

Composite Decking

£60-£120 / $75-150 per m²

Low maintenance, durable, eco-friendly

🔧

WPC Decking

£50-£100 / $65-130 per m²

Wood-plastic composite, weather resistant

🌿

Hardwood Decking

£80-£200 / $100-250 per m²

Premium, exotic, long-lasting

What is a Decking Calculator?

Why Use a Decking Material Calculator?

A decking calculator is an essential tool for anyone planning to build a garden deck, patio deck, or rooftop terrace. It eliminates guesswork by calculating exactly how many decking boards, joists, screws, and concrete footings you need based on your deck dimensions.

Using a deck estimator prevents costly mistakes like buying too much material (wasting money) or too little (delaying your project). It also helps you compare costs between different decking materials like wood, composite, or WPC.

What This Calculator Provides

Total deck area in square meters or feet
Number of decking boards needed
Number of joists required (with spacing)
Screw/nail quantity estimate
Concrete footings for support posts
Estimated total project cost

Decking Calculation Formulas (2026 Standard)

Deck Area = Length × Width
Boards Needed = Deck Area ÷ (Board Width × Board Length) + 10% Waste
Joists Needed = (Deck Width ÷ Joist Spacing) + 1 × (Deck Length ÷ 4)
Screws Needed = Boards × Average 30 screws per board
Concrete Footings = (Deck Length ÷ Post Spacing + 1) × (Deck Width ÷ Post Spacing + 1)

How to Use the Decking Calculator

Step 1: Measure Your Deck Area

Measure the length and width of your planned deck area in meters or feet. For irregular shapes, break them into rectangles and calculate each section separately.

Step 2: Select Decking Material

Choose between timber, composite, WPC, or hardwood. Each has different board sizes, prices, and installation requirements. Composite boards are often longer but narrower than wood.

Step 3: Enter Board & Joist Specifications

Enter your chosen board width (typically 90-150mm), board length (2.4m, 3.6m, 4.8m), joist spacing (400mm or 450mm center-to-center), and post spacing (1.2m-1.8m for support).

Standard Decking Material Requirements (Per 10m² Deck)

Material Type	Boards Needed	Joists Needed	Screws Needed	Concrete Footings
Pressure Treated Wood	55-65 boards	15-18 joists	1,200-1,500 screws	4-6 footings
Composite Decking	45-55 boards	15-18 joists	1,000-1,300 screws	4-6 footings
WPC Decking	50-60 boards	15-18 joists	1,100-1,400 screws	4-6 footings
Hardwood Decking	55-65 boards	15-18 joists	1,200-1,500 screws	4-6 footings

Decking Cost Comparison (2026 UK & US Prices)

Material Type	Material Cost/m²	Installation Cost/m²	Total Cost per m²	20m² Deck Total
Pressure Treated Wood	£30-50 / $40-65	£40-60 / $50-75	£70-110 / $90-140	£1,400-2,200 / $1,800-2,800
Composite Decking	£60-120 / $75-150	£50-80 / $60-100	£110-200 / $135-250	£2,200-4,000 / $2,700-5,000
WPC Decking	£50-100 / $65-130	£45-70 / $55-90	£95-170 / $120-220	£1,900-3,400 / $2,400-4,400
Hardwood Decking	£80-200 / $100-250	£60-100 / $75-125	£140-300 / $175-375	£2,800-6,000 / $3,500-7,500
Average Total	£2,075-3,900 / $2,600-4,925 per 20m² deck

Complete Deck Building Guide (2026)

📐 Deck Design Considerations

Deck height: Ground-level (0-30cm) or raised (30cm+)
Shape: Rectangle, square, L-shaped, or curved
Intended use: Dining, lounging, hot tub, or multi-purpose
Local building codes and permits required
Sun exposure and drainage planning

🛠️ Material Checklist

Decking boards (main surface)
Joists (support structure under boards)
Support posts and beams
Concrete footings or post anchors
Hidden fasteners or deck screws
Framing hardware (joist hangers, brackets)
Waterproofing membrane and weed barrier
Balustrades and handrails (if raised deck)

Joist Spacing & Board Recommendations by Material

Pressure Treated Wood

Joist spacing: 400-450mm (16-18 inches) center-to-center
Board thickness: 25-32mm
Board width: 90-150mm
Best for: Traditional natural look, budget-conscious projects

Composite Decking

Joist spacing: 350-400mm (14-16 inches)
Board thickness: 20-25mm
Board width: 140-160mm
Best for: Low maintenance, modern appearance, long life

WPC Decking

Joist spacing: 400-450mm (16-18 inches)
Board thickness: 22-28mm
Board width: 140-150mm
Best for: Coastal areas (salt resistant), humid climates

📝 Example Calculation: 4m x 5m Deck (20m²)

Pressure Treated Wood (140mm wide boards, 400mm joist spacing):
• Decking boards needed: 4m ÷ 0.14m = 29 boards × 5m = 145 linear meters ÷ 4.8m per board = 31 boards + 10% waste = 34 boards
• Joists needed: 5m ÷ 0.4m spacing = 13 joists @ 4m each = 52 linear meters
• Screws needed: 34 boards × 30 screws = 1,020 screws
• Estimated material cost: 20m² × £40 = £800 + 20% contingency = £960
• Total project cost (with installation): 20m² × £100 = £2,000

Expert Tips for Your Decking Project

✅ Pro Tips

Always add 10-15% waste allowance for cuts and mistakes
Use hidden fasteners for a clean, screw-free surface
Leave 5-8mm gap between boards for water drainage and expansion
Install weed barrier fabric under joists to prevent plant growth
Treat cut ends of pressure-treated wood with preservative
Use stainless steel or coated screws for composite decking

⚠️ Common Mistakes to Avoid

Not checking local building codes before starting
Insufficient joist spacing causing bouncy deck
Forgetting to account for steps, railings, and skirting
Ordering materials before verifying final deck dimensions
Not allowing for ground settlement over time
Using wrong fasteners for composite materials

Decking Maintenance Guide by Material (2026)

Wooden Deck Maintenance

Clean: Annually with deck cleaner
Treat: Every 1-2 years with wood preservative
Seal: Every 2-3 years with waterproofer
Sanding: Every 2-3 years if surface becomes rough
Lifespan: 10-15 years with proper maintenance

Composite Deck Maintenance

Clean: Twice yearly with soap and water
Treat: No sealing or staining required
Inspect: Annually for damage or loose boards
No sanding needed
Lifespan: 25-30 years with minimal maintenance

WPC Deck Maintenance

Clean: Twice yearly with mild detergent
Treat: No sealing required
Inspect: Annually for mold (unlikely but possible)
No staining needed
Lifespan: 20-25 years

Frequently Asked Questions About Decking Calculators

How many decking boards do I need for 10m²?

For a 10m² deck (e.g., 3.16m x 3.16m), you typically need 50-60 boards of standard 140mm width and 3.6m length, including 10-15% waste allowance for cuts and mistakes.

What gap should I leave between decking boards?

Leave a 5-8mm gap between boards for water drainage, debris passage, and seasonal expansion. Composite boards may require larger gaps (6-10mm) due to higher thermal expansion.

How do I calculate joist spacing for decking?

Divide your deck width by the joist spacing measurement (typically 400-450mm for timber, 350-400mm for composite). Add 1 to account for the end joist. Example: 4m deck ÷ 0.4m spacing = 10 + 1 = 11 joists.

What is the cheapest decking material?

Pressure treated softwood (pine/spruce) is the most affordable decking material at £30-50 per square meter. Composite and WPC are more expensive upfront but require less maintenance over time, potentially costing less in the long run.

How much does it cost to build a 10x10 deck?

A 3m x 3m (10ft x 10ft) deck costs approximately £700-1,100 for materials or £1,500-2,500 professionally installed using pressure treated wood. Composite would cost £1,200-2,000 for materials or £2,200-4,000 installed.

Do I need planning permission for a deck in the UK?

In the UK, decking may not require planning permission if it is less than 30cm above ground and covers less than 50% of the garden area. Always check with your local council as rules vary between England, Scotland, Wales, and Northern Ireland.

What is better: composite or wood decking?

Composite decking is lower maintenance, longer lasting (25-30 vs 10-15 years), and resistant to rot and splinters. Wood decking is cheaper initially, looks more natural, and can be sanded and refinished. Choose based on budget and how much maintenance you want to perform.

How many footings do I need for a deck?

Footings are typically spaced 1.2-1.8m apart. For a 4m x 5m deck, you would need approximately 9 footings (3 along length × 3 along width). Use our footing calculator above for exact numbers based on your deck dimensions.

Helpful Decking Resources

UK Resources

Planning Portal - Decking regulations
Wickes - Decking buying guides
B&Q - Decking installation videos
Ecodek - Composite decking specialists

US Resources

TimberTech - Composite decking
Trex - Deck design tools
Home Depot - Decking installation guides
Lowe's - Deck material calculator

Disclaimer: This decking calculator provides estimates for informational purposes only. Actual material requirements and costs vary based on site conditions, local building codes, chosen materials, contractor rates, and regional price variations. Always consult a professional contractor and obtain multiple quotes before proceeding with any construction project. Verify all local building codes and permit requirements before starting work.