Roof Tiles Calculator

The number of roof tiles depends on the roof area, tile type and pitch angle. Common UK roof tiles include concrete interlocking (approximately 10 tiles per m², with profiles such as Marley Modern and Redland 49 covering 9-12 per m²), clay plain tiles at 270×165mm (approximately 60 tiles per m²), clay pantiles at 280×240mm (16-18 per m²) and slate (approximately 20–30 per m² depending on size). The coverage rate accounts for the overlap (gauge) between rows. Add 5-10% waste for cuts at edges, hips and valleys, so a 60 m² roof at 9 tiles/m² needs 540 tiles, or 594 once 10% waste is included.

Roof area is measured on the slope, not the floor plan. For a simple pitched roof, each side is calculated as rafter length × eaves-to-eaves width. The rafter length depends on the pitch angle and the horizontal span: at 30°, the rafter is about 15% longer than the horizontal distance, and at 45° about 41% longer. On an 8 m × 5 m gable roof at 35°, each rafter is 3.05 m, each side is 24.4 m² and the whole roof is 48.8 m². At 10 tiles/m² that is 488 tiles, or 513 with 5% waste, plus 25 ridge tiles along the 8 m ridge at 0.33 m each.

Enter the roof dimensions, pitch angle and tile type. The calculator shows total roof area (on slope), number of tiles, ridge tiles, hip tiles (if applicable) and estimated weight per m². Hips, valleys and ridges need special tiles ordered separately from the field tiles. Roof weight matters for structural calculations: concrete tiles weigh approximately 43 kg/m², while natural slate is about 30 kg/m², so swapping slate for concrete on an old roof is not a like-for-like change.

Tile prices per m² diverge sharply once you factor in how many are needed. Concrete interlocking tiles, the most common choice on new builds, cost £0.80-£1.80 each, or £8-£18/m². Clay plain tiles are £1.50-£4 each but, because so many are needed, work out at £80-£200/m². Clay pantiles cost £2-£6 each (£40-£90/m²), natural slate from Wales, Spain or Brazil £2-£8 each (£40-£140/m²) and man-made synthetic slate £2-£3 each (£25-£50/m²). In conservation areas you will often be required to match the original roof, which usually means clay or natural slate.

What sits beneath the tiles is specified alongside them. Roofing battens of 38×25mm are fixed at the gauge required by the particular tile, and below them goes roofing felt or, preferably, a modern breathable membrane that lets moisture escape while keeping rain out and catches water if a tile slips. Insulation is either 270mm in the loft or foam or rigid board between the rafters for a warm roof. Ridge tiles are bedded in mortar in the traditional way or fitted as a dry-ridge system, which is ventilated and needs no maintenance. Building Regulations require all new roofs to meet the U-value targets in Part L.

Re-roofing costs in the UK break down into materials at £15-£40/m² for concrete tiles or £80-£200/m² for clay or slate, plus labour at £40-£90/m². A typical semi-detached roof of 60 m² comes to £3,500-£8,000 in concrete, £6,000-£12,000 in clay and £8,000-£15,000 or more in natural slate. Scaffolding adds £600-£1,500, skip hire for the old tiles £200-£400, and specialist removal of asbestos slates £1,500-£4,000 or more. Most quotes include felt, battens and breathable membrane, but check before comparing them.

Lifespan varies as much as price. Concrete tiles last 30-50 years, clay plain tiles 60-80 years, clay pantiles 60-100 years and natural Welsh slate over 100 years, with some Victorian roofs still on their original slates. Brazilian and Spanish slate is more variable at 30-50 years, and synthetic slate also sits at 30-50. The signs that a roof needs more than a repair are many broken or slipped tiles, loose ridge tiles, felt visibly damaged from inside the loft, water staining on ceilings, heavy moss or lichen and a sagging roofline. As a rule of thumb, once 15% or more of the tiles are broken or damaged, a full re-roof is more economical than patching.