Board and gap aware
Uses the actual board width, stock length and side gap rather than dividing deck area by a generic board size.
Free professional trade tool
Free Decking Calculator
Calculate decking boards from the actual board width, stock length and gap, then add waste, estimate joists and fixings, include fascia and work out an optional material cost.
Board quantity and lineal length
Straight, diagonal and framed layouts
Joists, fixings, fascia and cost
No sign-up required
1
Measure the deck
Add one rectangular deck or several separate sections. Deductions can remove planters, hot-tub openings, steps or areas that will not receive deck boards.
Deck sections
Measure each rectangle separately when the deck is L-shaped or split into levels.
Deductions
Optional. Remove any rectangular area that will not be decked.
Board quantity can be estimated from area, but rows, perimeter and substructure need dimensions.
Current net deck area12.00 m²
2
Enter the decking board and layout
Use the actual finished board width and stock length from the supplier. The side gap is included in the installed board pitch.
Suggested waste allowance
5%
A 5% starting allowance is suitable for a simple straight rectangular deck.
Trex describes 5% as a general rule of thumb for waste, while the Wickes decking calculator includes 10%. Diagonal boards, borders and awkward cuts can need more. Trex guidance · Wickes calculator
3
Estimate joists, fixings, fascia and cost
These are planning quantities, not structural design. Use the exact manufacturer instructions and local requirements for joist spacing, beams, posts, footings and connections.
Substructure and fixings
Joists are assumed to run perpendicular to the decking boards.
Percentage added for drops, damaged fixings and detailing.
Percent
Optional material cost
Leave prices blank when you only need quantities.
Built for real decking jobs
More than an area-only decking calculator
Plan boards around the actual product width and gap, then estimate the supporting materials needed to prepare a supplier order or customer quote.
Multiple sections and layouts
Add separate rectangles and choose straight, diagonal or picture-frame decking with an editable waste allowance.
Joists and fixings
Produces a planning estimate for joist lineal length, stock pieces and hidden clips or face screws.
Cost and PDF report
Add optional supplier prices, copy the result or print a clean one-page calculation for the job file.
Ready to price the labour and materials? Build a professional customer document with the free Quote Generator. After the work is complete, use the free Invoice Generator.
Keep every job, customer and payment organised
HandyMinder is a simple digital job diary for handymen and tradespeople who want their work details, payments and upcoming income in one clear place.
Useful things to know
Decking calculator questions
Practical guidance before ordering boards or building the frame.
How much extra decking should I allow for waste?
For a simple straight rectangular deck, 5% is a practical starting point and is the general rule of thumb described by Trex. The Wickes decking calculator includes 10%. Increase the allowance for diagonal boards, picture frames, several sections, short stock lengths or awkward cuts.
What gap should I leave between deck boards?
Use the exact installation guide for the selected product. Gap requirements change with material, profile and installation conditions. Trex, for example, specifies side-to-side gapping and explains that it is needed for drainage and movement. The calculator lets you enter the product-specific value rather than assuming one universal gap.
What joist spacing should I enter?
Enter the maximum spacing allowed by the exact board manufacturer and the chosen layout. Trex UK states that many of its boards can be installed on joist centres up to 400 mm, while angled installations can require closer framing. See the official installation guide for the product being used.
Why does the calculator not size beams, posts or footings?
Those components depend on loads, spans, ground conditions, deck height, connections and local rules, so an area calculator cannot determine them safely. Check with the relevant designer, building-control body or local authority. In the UK, planning permission and building regulations are separate systems and a project can require one, both or neither; start with the GOV.UK planning guidance.