Roof Tile & Slate Calculator

How this UK roof tile calculator works

Enter the building length and width at the wall plate, the eaves overhang, the pitch in degrees, and the waste percentage. Pick the tile or slate profile, enter ridge and eaves lengths, and the calculator returns the actual roof surface area in m², the tile count, the pallet count, the eaves course pieces and the ridge pieces — plus a material-only cost in pounds.

It supports the most common UK profiles: concrete plain tile, concrete interlocking, clay plain tile, natural slate, and steel corrugated sheet for outbuildings.

The math, derived from first principles

slope factor = 1 / cos(angle)
roof area = (length + 2×overhang) × (width + 2×overhang) × slope factor
tiles = roof area × pieces-per-m² × (1 + waste %)

A 12 × 9 m bungalow at 30° pitch with 0.4 m eaves overhang has a surface area of roughly 109.7 m². At 10/m² for Marley Modern interlocking tile and 10% waste that is 1,207 tiles, or 6 pallets at 240 tiles per pallet.

Tile-density quick reference (UK, 2026)

Densities verified against current Marley, Redland, Sandtoft and Russell technical data sheets:

Prices are merchant-bag, ex-VAT, before delivery; Checkatrade and MyBuilder quote installed rates of £45–80 per m² for concrete tile and £100–140 per m² for natural slate, including labour and breather membrane.

Common mistakes

Mixing pitch from a gable apex. UK pitches are quoted in degrees, not X/12 — confirm with the rafter set-out, not by eye. Below 22.5° most plain tiles are off-spec; below 17.5° most interlockings are off-spec without a high-performance underlay system.

Forgetting the eaves and verge tile-and-a-half. On a half-tile bond, every other course needs a tile-and-a-half at the verge. Add 5% to plain tile counts to cover this if you’re not buying tile-and-a-halfs separately.

Ridge under-counts on bonnet hips. Bonnet hip tiles cover ~3 per metre but each is a different piece from the ridge. Order them as a separate line. Standard angle ridges and roll-out ridges are simpler — roughly 3/m.

Code references

• BS 5534:2014 + A2:2018 — Slating and tiling, code of practice including mechanical fixing requirements.
• BS 8612:2018 — Dry-fixed ridge, hip and verge systems.
• NFRC Technical Bulletins — current versions cover ventilation, underlay class, and fixing patterns by wind zone.
• Approved Document C — Resistance to contaminants and moisture; applies to underlay choice and ventilation strategy.
• Approved Document L1B (2024 update) for thermal performance when reroofing — affects insulation depth at the eaves.

How this calculator differs

The material takeoff calculator gives a full reroof bill including battens, underlay, breather membrane, fasteners, and ventilation. The roof area calculator gives just surface area for any of four shapes. This tile calculator sits in between — surface area plus the tile-product line items that go on a merchant order.

For a budget figure, run the roof cost calculator with your m² number; for layout planning, use the area calculator first to choose between gable and hip on the same footprint.

Putting it together

Run the calculator, write down the tile count, the pallet count and the ridge count, then check with your merchant — Jewson, Travis Perkins and Selco all price by pallet for orders above one. A typical 110 m² bungalow re-roof in concrete interlocking tile costs roughly £3,500 in tiles and £4,500–£8,800 installed; on natural slate the same job is closer to £11,000–£15,400 installed.

The tile count is the foundation of your merchant order — get it right and the rest of the reroof falls into place.