How to Work Out Your Decking Materials

Two easy ways to calculate what you need – from Wood Green Timber

Planning a decking project but not sure how much timber you’ll need? We’ve got two simple ways to help you work it out. Whether you want to measure it out the long way or use a quick square metre rule of thumb, this guide will keep you on track.

Step 1: Measure Your Deck Area

Start by measuring the total width and length of your decking area in metres.

Example:
4.8m long x 3.6m wide = 17.28m²

Option 1: Calculate Decking Boards Manually (Board by Board)

Decking boards are typically 145mm wide, but when you allow for spacing, you’ll want to work on 150mm (0.15m) total width per board.

Formula:

Deck width ÷ 0.15 = number of boards across
Deck length ÷ board length = rows (if not full-length boards)

Example:
3.6m ÷ 0.15 = 24 boards
Laid along the 4.8m length = 24 full-length boards
Add 10–15% for trimming and waste = ~27 boards total

• Great if your boards run the full length of the deck

• Helps visualise layout

Option 2: Use the m² Shortcut (Quick & Easy)

If you're working out square metres, a quick rule is:

1m² = approx. 7 linear metres of decking board

So just multiply your total m² by 7 to get your total linear metres.

Example:
4.8m x 3.6m = 17.28m²
17.28 x 7 = 120.96 linear metres of decking

If you’re using 4.8m boards:

120.96 ÷ 4.8 = ~25.2 boards → Round up to 27 boards including waste

• Fast, no faffing

• Great for rough quotes or when you’re pressed for time

• Used by our team at the counter all the time

Don’t Forget the Joists

• Space joists at 400mm centres

• Run them opposite to your deck boards

• Use the same method to calculate how many you’ll need based on spacing

Need help with that? Check out our How to Build a Deck Subframe guide or give us a shout.

Example Shopping List (4.8m x 3.6m Deck)

• 27 x 145mm decking boards @ 4.8m

• 9 x 47x150mm joists @ 4.8m

• 2 extra joists for noggins

• Weed membrane

• Box of decking screws

• Fascia or trims

• Postmix and 100x100 posts if needed

Need Help? Just Ask

Bring us your sketch, measurements, or even a photo of the space — we’ll help you figure out what you need. No guesswork, no pressure — just proper service and the right timber for the job.

Wood Green Timber — real materials, real advice, real people.