Roof tile and slate calculator: how many tiles or slates per m²?

Measure one slope of your roof and the calculator works out how many tiles or slates you need, plus the battens and breathable underlay to order. Double the result for both sides of a pitched roof.

How it works

1. 1Measure the slope — the length from ridge to eaves (or verge), and the height up the slope, not across the house. On a pitched roof measure each side separately, or measure one and double it.
2. 2Pick your covering. Clay plain tiles work out at about 60 per m²; concrete interlocking tiles about 10 per m²; natural or fibre cement slates about 20 per m² with a 100mm headlap.
3. 3Add a waste allowance. Interlocking tiles waste little, so 5% is usually enough. Plain tiles and slates get cut at verges and hips — allow 10%.
4. 4Check the underlay and battens. The calculator includes breathable membrane (45m² per roll once laps are allowed for) and treated 50×25mm battens cut to your tile gauge.
5. 5Don't forget the extras — ridge and verge tiles (roughly 1.5 per metre of ridge), nails, clips and lead flashing where the roof meets a wall.

Common roofing quantities

• Single garage roof, 6m × 3m one slope — 18m² before waste. Use the covering and waste options above to estimate the tiles, battens and underlay.
• Pitched extension roof, 5m × 3.5m per side — 17.5m² per slope, or 35m² for two identical slopes before waste. Select the covering's stated gauge and allowance above.
• Slate re-roof, 8m × 4m per slope — about 32m² per slope before waste. Slate size, headlap and manufacturer coverage determine the count; confirm the specification before ordering.

Steep or shallow roofs change the maths: the flatter the pitch, the smaller the slope height for the same house — so always measure up the slope itself rather than working it out from the floor plan.

Working from a floor plan? Use the pitch factor

A plan drawing shows the roof's footprint, not its slope. Multiply the plan area by the pitch factor (1 ÷ cos of the pitch) to get the real area you tile. Don't know the pitch? Work it out with the roof pitch calculator.

Worked example: a 6m × 5m garage footprint is 30m² on plan. At a 45° pitch that's 30 × 1.41 ≈ 42.4m² of roof. With concrete interlocking tiles at about 10 per m² plus 5% waste, that's roughly 446 tiles — before ridge, hip and verge pieces. Hips, valleys and dormers change the count, so check against your drawings.

What this calculator covers

The tool prices the covering and the fixings that go with it. Enter the slope length and height in metres, pick your covering, and it works out the quantities below.

• Clay plain tiles — about 60 per m², the traditional small tile seen on older roofs; allow 10% for cuts at verges and hips.
• Concrete interlocking tiles — about 10 per m², the common choice on modern estates; 5% waste is usually enough.
• Natural and fibre cement slates — about 20 per m² with a 100mm headlap; check the lap your slate needs, as it changes the count.
• Battens and underlay — treated 50×25mm battens cut to your tile gauge, and breathable membrane at 45m² per roll once laps are allowed for.

How many tiles and slates per m²?

Quick answer: about 60 plain tiles, 10–11 large interlocking tiles, or 13–27 natural slates per m² of roof slope, depending on size and headlap. These are the makers' own net figures — add 5–10% for waste and cuts.

Measure the slope, not the floor plan — a steeper roof has more area than its footprint. Use the roof pitch calculator to turn a plan size into slope area, and the Cupa Pizarras slate coverage guide for other slate sizes and laps. The headlap your roof needs depends on pitch and exposure under BS 5534 — confirm it with your roofer.

Sources: Marley plain tile and Modern technical data, BMI Redland Renown data sheet (October 2025), Cupa Pizarras slate coverage table. Checked 4 November 2026.

How many composite slates per m²?

Composite (recycled plastic and mineral) slates are laid to a gauge set by the roof pitch, so the count per m² changes with the pitch. These are the manufacturer figures for two common UK ranges — other ranges differ, so use the figure printed for yours.

Sources: Tapco coverage from the NBP Tapco Slate listing; Envirotile from The Plastics Shed. Checked 31 October 2026.

Example: a 20m² slope at 35° with Tapco Slate is 20 × 18 = 360 slates, plus 10% for cuts at verges and hips ≈ 396 slates. Ridge, hip and starter pieces are extra.

Working on the walls too? The insulation calculator covers loft and rafter insulation, and the timber cutting calculator helps with rafters and joists. See all Price Planter calculators.

Tile and slate coverage figures are typical UK allowances and vary by manufacturer — always check the coverage stated on the product, and confirm the spec with your roofer before ordering.

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