Free tool
Cost estimator
Pick a project type and, where a per-m² rate exists, enter an approximate size to get an indicative range calculated from published UK industry rates.
Every figure this tool uses comes from a named public source (see the citation under each result) — never a Homespace quote. Where no reliable per-m² rate exists for a project type, the tool shows the published range directly instead of calculating one.
Estimated range for 25m²
£45,000–£75,000
Based on the published rate of £1,800–£3,000 per m² — see below.
| Range | ||
|---|---|---|
| General rate | £1,800–£3,000 | Per m² |
| 20m² extension | £40,000–£56,000 | Total project |
| 30m² extension | £60,000–£84,000 | Total project |
| 50m² extension | £100,000–£140,000 | Total project |
Sources: HomeOwners Alliance (2026 guide), Checkatrade (updated June 2026, figures exclude VAT), Federation of Master Builders (UK average, no date shown on source page)
This is a published industry guide range, not a Homespace quote.
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