Build cost calculator for extension, refurbishment and new build

We have developed four different sophisticated cost per square metre calculators – one for extensions, one for loft conversions, one for refurbishment projects and one for new builds, and all of them updated for 2026 price per square metre build cost prices for London and the UK.

Just pick the construction cost calculator below that matches the type of project you are considering. Put in the basic details of your scheme and it will quickly calculate the build cost of your extension, loft conversion, refurbishment or new build house.

The estimated build cost shown below will give a very good indicator of the likely costs for building or refurbishing your project – but do remember it is always possible to further save on these costs by planning ahead, engaging a well-established residential architecture company and choosing the right builder.

Having spent years delivering architect services and working directly with builders on projects across London and the UK, we know where things go wrong and how to stop them before they do. Our proven processes and hands-on construction inspection approach are designed to keep your project on time, on budget and as stress-free as possible.