How deep should pergola posts be set in the ground?

Pergola posts should be set at least 600mm deep (one quarter of the above-ground height is a good rule). Use postcrete or concrete at a ratio of about 2 bags of postcrete per post. The hole should be about 300mm in diameter.

What is the best timber for a pergola?

Pressure-treated softwood (UC4 rated for ground contact) is the most common and cost-effective choice in the UK. Oak is a premium option that weathers beautifully. Cedar is naturally rot-resistant but expensive. All posts in ground contact must be UC4 treated.

What height should a pergola be?

A standard pergola height is 2.4m (8 feet) to the underside of the beams. This provides comfortable headroom. For areas near house walls, check local planning rules as structures over 2.5m may require planning permission. Allow for the beam and rafter depth on top.

Do I need planning permission for a pergola?

In most cases, a garden pergola falls under permitted development in the UK provided it is no higher than 2.5m if within 2m of a boundary, does not cover more than 50% of the garden, and is not in front of the house. Always check with your local planning authority.

WoodCalcs

Pergola Calculator — Timber Quantities for Pergola Build

Calculate timber quantities for pergola posts, beams, and rafters.

Pergola Length

Direction beams run

Pergola Width

Direction rafters span

Height (above ground)

Post Size

Rafter Spacing

Timber Price per Metre (optional)

How We Calculate This

This calculator determines the timber quantities for a standard rectangular pergola.

Component calculations

Posts: 4 (up to 3m long) or 6 (over 3m) x (Height + 600mm burial depth)

Beams: 2 x (Pergola length + 300mm overhang)

Rafters: ceil(Length / Spacing) + 1 x (Width + 300mm overhang)

The 150mm overhang on each end of beams and rafters is standard for a traditional look. Post length includes 600mm for burial in the ground with concrete.

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify measurements and material quantities before cutting or purchasing.