Extension Cost Calculator

Residential Build Costs Calculator

This extension cost calculator provides a helpful tool for assessing the financial outlay required for your building project. It breaks down the various elements that make up the total price, allowing you to see how various factors impact your extension cost per square metre.

Whether you’re planning a single storey extension or something bigger, this tool will enable the calculation of a sensible estimate of your house extension cost per m2, whatever size and specification of extension you are planning.

1 How have you measured your space?

Either is fine, our tool will give you an accurate estimate whichever option you choose.

Metric (m)

Imperial (ft)

2 Extensions

If your project includes any areas of “new-build”construction such as a kitchen extension to the side or rear of your home, a new basement or maybe a garden out-building, please enter the floor area of this part of the project.

Sq. M

3 Remodelling

If your project includes any remodelling of existing space involving some construction such as a new staircase, knocking through a wall or removing a chimney breast etc., please enter the floor area of this part of the project.

Sq. M

4 Fitting Out

Including all the above areas, please enter the total floor area to be fitted out? Fitting out work includes such things as heating, kitchens, painting & decorating, floor finishes, bathrooms, joinery, lighting & electrical work etc.

Sq. M

5 Level of specification

Are you looking for a basic job or something more high spec? Labour intensive fine finishes & expensive or bespoke components will be more costly than basic items available off the shelf at the builder’s merchant.

Basic High Specification

6 Complexity

Are the proposals simple and straight-forward to build? Do the works involve complex structural or constructional difficulties or a great deal of ground-work and excavation? How easy is working access to the site and how much space will there be to operate?

Straight Forward Complex

7 The Builder

Different builders can give radically different prices on the same specific proposals. Generally the better quality of work and the better organised they are, the more expensive they will be. Low cost will usually mean a compromise on quality, organisation or both.

Low Cost High Quality

8 Region/Area

Not only will local rates of pay vary regionally across the country (which will affect your builder’s costs), but also the reality is that builders will generally charge more when the project is located in a more expensive residential area that in a lower cost area.

Affordable Expensive

9 Using an Architect / Designer?

How much involvement are you planning for architects/designers for this project?

Not at all Intensive Involvement

How Much Does an Extension Cost?

When planning an extension or renovation, it’s vital to grasp all the factors influencing the costs from the beginning. Understanding these elements helps avoid expensive errors later in the project.

Your architect plays a crucial role in helping you realise your dream space while staying within budget. Their extensive knowledge and experience will not only reveal what’s achievable but will also guide you through the expected financial implications, highlighting potential pitfalls to avoid.

A lot of the budget variance depends on you and the choices you make. With the help of our construction cost calculator, this cost estimator will help you get an idea of what you might have to spend. Our online estimator allows for dynamic adjustments—if the figures are higher or lower than your expectations, you can easily modify your inputs to see how changes affect the cost. This flexibility ensures you can continuously refine your plans until they perfectly align with your financial boundaries.

Need any further help, other information or assistance? Please get in touch below

First name*
Last name*
Email address*
Phone number*
Address line 1*
Address line 2
City/town
Postcode*
How did you hear about us?*
Project budget
Project information*
Marketing consent*
- By entering your details, you're allowing us to use the information to help you and get in touch with you. Don't worry, you can request for us to delete your data at any time.
Phone
This field is for validation purposes and should be left unchanged.

Residential Build Costs Calculator

Needing to Calculate Architect Fees?

Use our Extension Cost Calculator UK to get an Estimate

Projected total cost

£0.00

How Much Does an Extension Cost?

Need any further help, other information or assistance? Please get in touch below

My tooltip