Two ways to price timber: a simple total-length run for rails, edging and framing, or the pergola planner — enter footprint, height and post count and it works out posts, two beam runs and rafters at the standard 600mm spacing.
The value engine mixes 3.6m and 4.8m lengths for the cheapest total with least waste, and automatically steps rafters up to 200×50 timber when your pergola depth spans more than 3 metres — the point where 150×50 starts to sag.
01 — The Calculator
Pick a material, pace out your plot, and the value engine prices every way to fill it — hippo bags, dumpy bags or handy sacks.
Enter dimensions to calculate.
Timber length
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Pieces in mix
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4.8m rails
0 full
Left over
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Best price
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We mix 2.4m posts, 3.6m and 4.8m rails for the cheapest fit — for a pergola, add up the lengths of every post, beam and rafter.
Enter your plot dimensions and the value engine will price the cheapest way to cover it.
Worked example: 3×3m pergola on 4 posts
A 3×3m pergola with 4 posts needs 4 × 2.4m posts, about 6.6m of beam (two sides plus overhang) and 6 rafters at 600mm centres — around £163 all-in using a mix of 3.6m and 4.8m rails. A plain 20m timber run comes to about £93.40 with the same mixing trick.
600mm centres is the standard for garden pergolas — close enough to support climbing plants and shade fabric without the timber cost of tighter spacing. The planner uses 600mm and rounds up, so you always have enough.
Garden Calculator — Project
My garden project · 29 September 2026
| Item | Qty | Each | Total |
|---|---|---|---|
| Estimated total | £0.00 | ||
Prices from the Garden Calculator sample trade catalogue — confirm with your merchant before ordering.