Decking Calculator

Plan your timber or composite deck in seconds — get exact board, joist, noggin and screw quantities from your deck dimensions, plus a full cost estimate.

Built for UK tradespeople, garden builders and DIYers, Decking Calculator handles the maths so you can focus on the build. Enter your deck length and width, pick your boards and joist setup, and you're done.
WHAT IT CALCULATES
• Decking boards — count, including waste allowance
• Joist count and total joist timber needed (in metres)
• Noggins — quantity and total length, sized for your spacing
• Decking screws or composite hidden clips — total count plus number of boxes/packs
• Total deck area in square metres
• Optional cost breakdown — boards, joist timber and fixings totalled in £
UK MATERIAL PRESETS
• Softwood: 150×32mm and 120×28mm
• Composite: 150×25mm and 140×25mm (uses 1 hidden clip per joist crossing)
• Board lengths: 2.4m, 3.0m, 3.6m, 4.8m
• Joists: 47×150mm and 47×100mm with C16 span limits built in
• Joist centres: 400mm or 600mm
BUILD-SAFETY WARNINGS
The app warns you when your design is unsafe or wasteful:
• Joist span exceeded — your deck width exceeds the safe span for your joist size and spacing (C16 softwood)
• Unsafe board/spacing combination — 600mm centres with 28mm or thinner boards
• Board joints landing mid-bay — your board length isn't a multiple of joist spacing, so butt joints won't land on a joist
• Composite board reminder — switches the calculation to hidden clips automatically
TWEAK EVERYTHING
• Board gap (3–10mm)
• Waste allowance (0–25%)
• Optional pricing per board, per joist metre and per box of fixings
WHO IT'S FOR
• Carpenters, joiners, landscapers and decking installers quoting jobs
• Self-builders working out a materials list for the merchant
• Anyone planning a garden deck and wanting to budget accurately
Free with a small banner ad. One-off in-app purchase to remove ads.
Disclaimer: results are estimates only. Always verify quantities against your specific design and follow your local building regulations.