Roofing Calculator guide
Roofing Calculator: Roof Area and Tiles Needed
Use our roofing calculator to work out the area of a pitched roof from the building size and pitch, and how many tiles or slates you need.
By the AllCalculator editorial teamUpdated 16 October 20261 min read
Whether you're getting quotes or planning a re-roof, you need to know your roof's area. Our Roofing Calculator works it out from the size of the building and the roof pitch.
How to use the calculator (Roofing Calculator)
- Enter the building's length and width.
- Enter the roof pitch in degrees.
- Enter the overhang at the eaves and verges.
- Choose your roof covering, or enter your own coverage per m².
How it works
For a simple pitched roof, the sloping area is the footprint divided by the cosine of the pitch:
Roof area = plan area ÷ cos(pitch)
The steeper the roof, the bigger the area compared with the footprint.
Typical coverage
| Covering | Pieces per m² (approx.) |
|---|---|
| Concrete interlocking tiles | 10 |
| Natural slates (500 × 250mm) | 20 |
| Plain clay or concrete tiles | 60 |
A worked example
With the calculator's default settings, a 10m × 8m building with a 35° roof and a 0.3m overhang has a plan area of 91.2m² and a roof area of 111.3m². That needs about 1,225 interlocking tiles, including 10% for waste.
Frequently asked questions
Do I need planning permission to re-roof?
Usually not, if you're replacing like for like and not raising the roof. Listed buildings and conservation areas have extra rules.
What about hips and valleys?
They need extra cutting and special fittings, so add more for waste. Ridge, hip and verge tiles are ordered separately.
Can I use any tile at any pitch?
No. Each tile has a minimum pitch. Check the manufacturer's guidance.
For a natural slate roof, see our Slate Roof Calculator, and for flat roofs, the Flat Roof Cost Calculator.
Sources and further reading
Links open official and independent websites in a new tab.
This guide is general information to help you understand your options. It isn't financial, tax, legal or building advice and doesn't take your personal circumstances into account. Figures were checked when the guide was last updated and can change, so confirm anything important with GOV.UK, HMRC, a regulated adviser or a qualified tradesperson.