A construction cost calculator turns floor area in square metres into a build budget: area × a per-m² rate for the project type, adjusted for region and specification. The result is a low, likely and high cost range you can use before a design is finalised.
This page is for builders, contractors, quantity surveyors and architects pricing work for their own clients, who need a fast planning figure before committing to a full measured estimate. The calculator below does it instantly using current UK rates.
Key takeaways
- UK building work typically costs £1,400 to £3,000 per m² in 2026, depending on project type, specification and region.
- A construction cost calculator turns that range into a project-specific low, likely and high figure in minutes.
- Labour makes up around 40 to 45% of a typical build, so it is the single biggest variable to get right.
- UK building material prices rose 6.0% in the year to June 2026, so a rate list more than a year old has drifted.
- A per-m² figure is a planning range, not a quote: always check it against a measured estimate before pricing a client.
- Hold a contingency of 10 to 15% on top of the headline figure for the items a per-m² rate does not capture.
How much does it cost to build in the UK in 2026?
Most UK building work costs £1,400 to £3,000 per square metre in 2026, depending on specification, location and project type. On that basis a standard new-build home averages around £250,000, while a detached four-bedroom house with a standard spec typically runs from £320,000 to £400,000 or more.
These are starting ranges, not fixed prices. Two projects of the same size can differ by tens of thousands of pounds once ground conditions, access and finish quality are factored in.
| Guide figure | Typical 2026 range | Source |
|---|---|---|
| Cost per square metre | £1,400–£3,000 | Checkatrade |
| Average UK new-build home | ~£250,000 | MyBuilder |
| Detached 4-bed, standard spec | £320,000–£400,000+ | MyBuilder |
| Labour as share of build cost | ~40–45% | Urbanist Architecture |
Build cost per m² by project type
A single UK-wide range hides a lot: an extension and a commercial fit-out do not price the same way per square metre. The table below gives example planning rates for the main project types, split by basic, standard and high specification. Each figure already carries preliminaries, site management, plant and waste for that project; it excludes land, fees, VAT treatment and fit-out, which are covered below.
| Project type | Basic spec | Standard spec | High spec |
|---|---|---|---|
| New build detached house | £1,800/m² | £2,200/m² | £2,800/m² |
| New build terrace or semi | £1,600/m² | £2,000/m² | £2,500/m² |
| Single storey extension | £1,800/m² | £2,400/m² | £3,200/m² |
| Double storey extension | £1,700/m² | £2,200/m² | £3,000/m² |
| Loft conversion | £1,400/m² | £1,900/m² | £2,600/m² |
| Garage conversion | £1,100/m² | £1,500/m² | £2,000/m² |
| Full house refurbishment | £900/m² | £1,400/m² | £2,000/m² |
These are example planning ranges built from current UK rates, not a fixed price for any one job. Check them against a measured estimate before a figure goes to a client.
Construction cost calculator: work out your build cost
Enter the floor area, project type and region to get a low, likely and high cost range for the whole project. Project type already accounts for storey count where it matters, a double storey extension carries its own rate because one roof and one foundation are spread over twice the floor area, which is why it costs less per m² than a single storey extension of the same size, not more.
Construction cost calculator
- Low estimate
- £97,240
- Likely cost
- £114,400
- High estimate
- £143,000
Example planning range built from current UK per-m² build rates. Excludes land, professional fees, VAT, kitchens and other fit-out, external works and contingency. Check against a measured estimate before quoting a client.
What a build rate includes and excludes
A per-m² rate is only useful if everyone agrees what it covers. A whole-project rate already carries preliminaries, scaffolding, welfare, plant, waste and site management, spread across the project's phases rather than added as a bare extra on top of a single task.
Included in the rate:
- Labour and materials for the structure, envelope and first and second fix
- Preliminaries, site setup, welfare, scaffolding and plant
- Waste removal and site management across the build
- Standard making good, plastering, decorating and cleaning
Excluded from the rate, and priced separately:
- Land purchase
- Professional and planning fees, including building control and a structural engineer where one is needed
- VAT, which depends on the type of work (see below)
- Kitchens, bathrooms and other fit-out beyond a basic specification
- External works and landscaping
- Abnormal groundworks (poor ground, high water table, contaminated soil)
- Contingency
Worked example: pricing a single storey extension
Here is how a builder would turn a per-m² rate into a real figure for a single storey rear extension with a 24 m² gross internal area, standard specification, built in the South East.
- Measure the GIA. The extension footprint, including internal walls, comes to 24 m².
- Pick the rate band. A single storey extension at standard spec sits at £2,400/m² from the table above.
- Apply the base cost. 24 m² × £2,400 = £57,600.
- Apply the regional factor. The South East carries a 1.15 multiplier: £57,600 × 1.15 = £66,240.
- Check prelims, overheads and profit are in the rate. The £2,400/m² figure already carries preliminaries, site overheads and the builder's margin, so none of those are added again at this step.
- Add contingency. A 10% contingency on £66,240 adds £6,624, giving a working budget of around £72,864.
That final figure is a planning budget, not a quote. Before pricing the job for a client, the extension should be measured properly and run through a full estimate.
How build costs vary by UK region
Location is one of the biggest drivers of cost, mainly because labour rates and site access vary so much across the country. The multipliers below are example factors against the UK average (1.00); London and the South East sit well above it, while the North East and Wales typically sit below it.
| Region | Example multiplier vs UK average |
|---|---|
| London | 1.30 |
| South East | 1.15 |
| South West | 1.05 |
| Midlands | 1.00 |
| North West | 0.95 |
| North East | 0.90 |
| Wales | 0.92 |
| Scotland | 0.95 |
| Northern Ireland | 0.88 |
This is exactly why a single UK-wide per-m² figure can mislead: the same house can cost noticeably more inside the M25 than in the North East, almost entirely because of labour rates and how easily materials and plant reach the site.
Why do building cost estimates go wrong?
Estimates go wrong when they lean on guesswork instead of current rates. UK construction material prices move constantly: government data shows the material price index for all construction work rose 6.0% in the year to June 2026 (GOV.UK). A figure that felt right last year can be well out of date by the time work starts.
The usual culprits:
- Out-of-date rates: using old material or labour prices in a market that shifted 6% in a year.
- Missing scope: forgetting groundworks, fees, waste or finishes in the headline figure.
- No contingency: leaving nothing for the unexpected on site.
- Ignoring location: applying national averages to a high-cost region.
Per-m² rate vs a measured estimate
A construction cost calculator gives an order-of-magnitude budget: enough to set a feasibility figure, secure early finance or compare two options, but built on averages rather than the actual quantities on your drawings. A measured estimate, taken from a bill of quantities or a detailed, elemental estimate, prices the real quantities of concrete, blockwork, timber and fixtures against current supplier and labour rates, so it carries far tighter accuracy.
Use the calculator at feasibility stage, when drawings may not exist yet. Once there are drawings to measure, or before any figure goes to a client as a quote, stop relying on a per-m² rate and have the job measured and priced properly.
How does VAT affect the figure?
Most domestic repair, maintenance and improvement work is standard-rated at 20% VAT. Qualifying new build work is zero-rated, so a self-build or a genuine new dwelling should not carry VAT on the build cost. A VAT-registered builder also reclaims the input VAT on materials they buy, so the headline per-m² build rate quoted in planning guides is generally stated net of reclaimable VAT, with VAT then added separately depending on the type of job. Always confirm the VAT treatment for the specific project before it goes into a client-facing figure.
How often should build rates be refreshed?
Material prices and tender prices move throughout the year, not just annually; the 6.0% rise in the material price index over the year to June 2026 shows how quickly a saved rate list can go stale. As a working rule, refresh per-m² rates at least quarterly, and immediately after any large move in steel, timber or energy prices. A spreadsheet of rates built a year ago, with nothing updated since, should not be trusted for a live quote.
What you need before using the calculator
Have these ready before entering figures, so the result is worth using:
- Measured gross internal floor area (GIA)
- Number of storeys
- Specification level (basic, standard or high)
- Ground conditions, as far as they are known
- Site access for materials, plant and skips
- Region
- Demolition or strip-out scope
- Any known abnormals (old drains, party walls, asbestos risk)
Costs a per-m² calculator usually misses
Even a good calculator misses the items that only show up once work is underway. The most common on UK jobs:
- Abnormal foundations where ground conditions are poor
- Drainage diversions
- Party wall work and surveyor fees
- Temporary works (propping, temporary roofs)
- Asbestos found during strip-out
Rather than absorbing these into the headline rate, flag each as a provisional sum in the estimate, with its own allowance and a note that it will be confirmed once the condition is exposed.
How is a calculator different from a quantity surveyor or a generic online tool?
A calculator sits between a full quantity surveyor and a generic online estimator: far quicker and cheaper than a QS, and far more accurate than a one-size-fits-all web tool built on global averages.
| Feature | Quantity surveyor | Generic online tool | Builder Expert calculator |
|---|---|---|---|
| Cost | High | Free/low | Low |
| Speed | Days | Instant | Instant |
| UK-specific rates | Yes | Rarely | Yes |
| Detailed breakdown | Yes | No | Yes |
| Updates with the market | Manual | Rarely | Regularly |
A quantity surveyor is still the right choice for large or complex jobs, where the fee is small against the risk of a wrong figure. For planning, comparing options and framing a budget before that stage, a calculator gives most of the accuracy in a fraction of the time.
Frequently asked questions
How accurate is a construction cost calculator?
It is accurate enough for planning, comparing options and setting a budget, built on current UK per-m² rates rather than a guess. It is not a substitute for a measured estimate once drawings exist.
Does it include VAT?
No. The per-m² rates are stated net of VAT; whether VAT is then added depends on whether the work is standard-rated repair and improvement or zero-rated qualifying new build.
What is not included in the figure?
Land, professional and planning fees, VAT, kitchens and other fit-out beyond a basic spec, external works and contingency are all priced separately from the build rate.
What is a good contingency percentage?
10 to 15% on top of the build cost is a reasonable working allowance for most domestic projects; higher-risk jobs with known abnormals should carry more.
Can it be used to quote a client?
No. Use it to set a budget or a feasibility figure, then confirm the price with a measured estimate before it goes to a client as a quote.
How does it differ from a quantity surveyor's cost plan?
A cost plan prices the actual quantities on a set of drawings, trade by trade. A per-m² calculator applies an average rate to a floor area, so it is faster but less precise, and is best used before drawings exist or to sense-check a cost plan.
Get a priced estimate, not just a planning range
A construction cost calculator is the right tool for an early budget. When it is time to price a real job for a client, Builder Expert gives you two ways to take it further: use our estimating software to turn your own measurements into a self-priced, itemised estimate in minutes, or send us the drawings and we will return a priced tender, detailed or basic estimate built by our estimators.
Register for free to try the software, or see our estimating prices for a fully priced estimate from your drawings.