Calculate tiles, battens and felt needed from roof area and pitch

Roof planes

Plane Shape Eave width (m) Plan run (m) Angle (°) Slope length (m) Tile type Tiles
Slope length is the rafter-length distance from eave to ridge along the pitch, not the horizontal plan run. Enter it directly, or leave it blank and fill in Plan run + Angle instead - slope length will be calculated automatically as plan run ÷ cos(angle). Hip end planes are estimated as a simplified triangle (half of eave width × slope length); dormer roof faces are treated as their own small rectangular plane. Always confirm complex hip and dormer takeoffs with a roofer.
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Area (m²)
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Tiles
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Battens
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Felt rolls

Tile courses, to scale

A representative gable cross-section, courses matching the tallest plane

Bill of materials

MaterialQuantity
Tile counts include a 5% wastage allowance for cuts and breakages; felt includes a 10% overlap allowance. Battens and felt rolls are rounded up to whole standard lengths/rolls. A rough ordering guide, not a cutting list - always confirm with your roofing supplier.

Tile types, at a glance

Tile typeTiles per m²Gauge (mm)
Approximate industry-standard figures - actual tiles-per-m² and gauge vary by manufacturer and product. Edit any figure to match your product's fixing specification, or add your own tile types. At least one tile type must remain, and a tile type in use by a roof plane can't be removed.

Roof tile and batten calculator

Work out how many roof tiles, tiling battens and rolls of felt or membrane you need. Enter each roof plane's eave width and either its slope length or its plan run and pitch angle, then pick a tile type. The calculator gives roof area, tiles with a 5% waste allowance, battens in 3.6 m lengths and 50 m² rolls.

It's free, works in your browser with no sign-up, and there's a free Windows app too.

Worked example: a 35° gable roof in concrete interlocking tiles

A semi-detached house has two equal roof slopes, each 8.4 m along the eaves with a 3.8 m plan run at 35°. The tile is the app's concrete interlocking default: 10 tiles per m² at a 345 mm gauge.

  1. Slope length: 3.8 ÷ cos 35° = 4.64 m.
  2. Area: 8.4 × 4.64 = 38.97 m² per slope, 77.9 m² in all.
  3. Tiles: 38.97 × 10 × 1.05 = 409.2, rounded up to 410 per slope, so 820 tiles.
  4. Batten courses: 4,639 mm ÷ 345 mm = 13.4, rounded up to 14, plus 1 for the eaves course = 15 courses per slope.
  5. Battens: 15 × 8.4 m = 126 m per slope, 252 m in all ÷ 3.6 m = 70 lengths.
  6. Felt: 77.9 m² × 1.1 overlap = 85.7 m² ÷ 50 m² = 1.7, so 2 rolls.

The app shows 77.9 m², 820 tiles, 70 battens and 2 felt rolls.

Questions

What is the batten spacing for a Redland 49 tile?

Batten spacing (gauge) for any named tile, the Redland 49 included, comes from the manufacturer's current technical data and depends on the headlap needed for your roof pitch and exposure, so check the product data sheet rather than relying on a generic figure. Once you have it, enter that gauge and tiles per m² in the calculator's Guide tab, or add the tile as a new type, and the batten and tile counts update to match.

How many roof tiles per m² do I need?

Tiles per m² is 1 divided by the gauge times the tile's cover width, both in metres, so it changes with the tile and the headlap you set. As a rough guide the app starts plain clay tiles at 60 per m², concrete interlocking tiles at 10 per m² and 500 x 250 slates at 20 per m², and you can overwrite any of these with the maker's figure.

How do I work out batten length per m² of roof?

Each course of battens runs the full eave width, so batten length per m² is roughly 1 divided by the gauge in metres - about 2.9 m per m² at a 345 mm gauge, or 10 m per m² at a 100 mm gauge. The calculator counts whole courses up the slope (slope length divided by gauge, rounded up, plus one for the eaves), multiplies by the eave width and rounds up to 3.6 m lengths.

How does roof pitch change the area to tile?

Tiles cover the sloping surface, not the plan footprint, so the slope length is the plan run divided by the cosine of the pitch angle. At 35° that adds about 22% to the plan area, and at 45° about 41%; enter plan run and angle and the app works out the slope length for you.

How many rolls of roofing felt or membrane do I need?

Take the roof area, add an allowance for laps and divide by the roll coverage. The calculator adds 10% for overlaps and rounds up to whole 50 m² rolls, so check the coverage of the roll you're actually buying.

How much waste should I allow for roof tiles?

The calculator adds 5% to the tile count for cuts and breakages and rounds each roof plane up to whole tiles. Hips, valleys and dormers create more cutting, so treat the result as an ordering estimate and confirm quantities with your roofer or supplier.

Roof Tile & Batten Calculator for Windows · More free construction calculators