Loft Conversion Cost Calculator
Estimate the cost of converting your loft into a bedroom, office or bathroom, by conversion type, floor area and finish quality, with a full cost breakdown and typical price range.
Estimate only. These are indicative 2026 UK estimates based on typical build rates, this is not a quote. Actual costs vary by region, access, structural condition and planning requirements. Always get itemised quotes from local builders before committing to a project.
Enter your floor area
Your estimated loft conversion cost and full breakdown appear here as you fill in the form.
How loft conversion costs are calculated
Loft conversion cost mainly depends on the type of conversion: a rooflight (Velux) conversion needs no change to the roofline and is cheapest; a dormer adds headroom and floor space; hip-to-gable and mansard conversions alter the roof structure and cost the most. We multiply an indicative build rate per square metre by your floor area and finish quality, then add a staircase allowance, an optional ensuite, building control fees and a design/architect fee. Treat the result as a starting point for budgeting, always get itemised quotes from local builders, as ground conditions, party wall agreements and planning requirements can all change the price.