Solar Roof Area Calculator

A typical 400W panel measures about 1722 × 1134mm, so it occupies roughly 1.95m² of glass — allow a little more for the 2-5cm gaps between modules. A 4 kWp system (10 panels) needs around 20m² of usable roof, and a 6 kWp system around 30m². Remember to deduct edge setbacks (400mm under MCS MIS 3002 V6.0) and the area around obstructions.

Measure the south-facing roof plane width and rafter depth. For a pitched roof, the slope area = depth ÷ cos(pitch angle). Deduct edge setbacks (400mm from all edges per MCS MIS 3002 V6.0, mandatory from 18 June 2026, unless extra wind-uplift fixings are used), obstructions (chimneys, vents, dormers) and any areas that are heavily shaded.

Yes, but hip roofs have less usable area than gable roofs because the triangular sections at each end are mostly unusable. A hip roof typically has about 75% of the usable area of an equivalent gable roof. The central rectangular section provides the most usable space.

MCS MIS 3002 V6.0 (mandatory from 18 June 2026) states modules should not be mounted within 400mm of any domestic roof edge unless additional wind-uplift fixings — and where needed extra roof timbers — are provided to resist the higher uplift forces in the edge zone. This supersedes the older 300mm figure. Exposed sites often warrant more; check the wind-load calculation for your site.

Yes, panels are mounted on angled frames (typically 10-15°) on flat roofs. Flat roofs allow flexible orientation but require row spacing to avoid inter-row shading (typically 1.5-2x panel height). This means fewer panels per m² than pitched roofs, but you can choose optimal orientation.

This tool uses 950 kWh per kWp per year — a UK-average figure for a south-facing array at 30-35°. Real output varies widely by region: MCS irradiance tables give roughly 837 kWh/kWp in Inverness up to about 1,132 kWh/kWp in Brighton, and east/west or shaded roofs yield less. Treat the estimate as a central guide, not a guarantee.

The cost estimate adds your per-panel price to a balance-of-system allowance (inverter, mounting, scaffold, labour and paperwork) that scales with system size at roughly £1,000 plus £900 per kWp. That sits in the 2026 UK market range of about £1,550-£1,700 per kWp installed — so a 4 kWp system is typically £6,500-£8,000 and a 6 kWp system around £10,000-£10,200. Eligible domestic solar is 0% VAT until 31 March 2027. Always obtain itemised quotes for your roof.