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Pergola calculator and 3D designer
Put a pergola over your deck, see it in 3D as you type the measurements, and get the posts, beams and rafters counted for you. Free, no sign-up, in metres or feet. Nothing is priced until you add your own supplier rates.
The rule in three lines
1. Posts first
Two rows, one each side of the deck. Two posts a side up to 14 ft of width, three a side beyond that.
2. A beam along each row
One beam per post row, running the length of the pergola and carrying the rafters.
3. Rafters across the width
Width divided by 20 in centres, rounded up, plus one. Close enough for shade and for a sail or lights later.
A worked example
- Deck under the pergola
- 16 ft x 12 ft, US practice
- Pergola posts
- 6 (three each side, over 14 ft wide)
- Beams
- 2, one along each post row
- Rafters at 20 in centres
- 11
- Clear height above the boards
- 8 ft
- Covered area
- 192 sq ft
Change the width and the rafter count moves with it. Every number on screen says which rule produced it, so you can check it before you order.
Common questions
How many rafters does a pergola need?
Rafters run across the width at 20 in centres, so it is the width divided by 20 in, rounded up, plus one for the last rafter. A pergola 16 ft wide works out at 11 rafters.
How many posts does a pergola need?
Two rows of posts, one each side. Up to 14 ft wide that is two posts a side, so four in total. Wider than 14 ft it goes to three a side, so six, to keep the beam spans sensible.
How high is the pergola in the model?
It stands 8 ft clear above the deck boards, which is the usual headroom once you allow for hanging lights or a shade sail. The posts land on the deck frame, not loose on the boards.
Does the pergola change the deck take-off?
Yes. Turning it on adds its posts, beams and rafters to the on-screen take-off and summary. The complete pack includes them in its order-ready PDF and CSV.
Does it tell me what the pergola costs?
Only with your own rates. Nothing is priced from a national average or a made-up figure. Enter what your supplier charges and the cost appears next to the quantities.
Is this a structural design?
No. It is a material take-off drawn from your measurements and the building practice of the country you pick. Loads, wind, soil and local approval are still your engineer's and your inspector's call.
The pergola is one part of the same list
Draw it once and the deck boards by buying length, joists, beams, posts, footings, stairs, railing, fixings and pergola are calculated together. The complete pack turns them into an order-ready PDF and CSV for your supplier.
Open my pergola in 3D, with the cut listFree, no account. Nothing is priced until you add your own rates. See a sample pack
Calculate my pergola