Free tools

London building calculators

Quick answers for homeowners, architects and site teams. Each one links to the London practices who can do the work.

What a London extension, loft or basement really costs, with fees, VAT and contingency.

Typical fees by project size, split across the RIBA Plan of Work stages.

Can your rear extension go ahead without planning permission?

When to expect a decision, with your borough's real approval rate.

Check a dormer and hip to gable against the 40 or 50 m³ limit.

The latest date to serve notice for your planned start.

Build up a wall or roof layer by layer and check it against Part L.

Rise, going, pitch and the 2R+G rule for a private stair (Part K).

Cubic metres, ready mix loads, and whether this week's weather suits a pour.

Bricks or blocks and mortar for a wall, with openings and waste.