How this is worked out
Tiles = roof area × tiles per m², plus your allowance for cuts and breakages. If you start from the plan, roof area = plan area ÷ cos(pitch).
Battens run across the slope at the gauge spacing, so metres of batten = area ÷ gauge in metres. We add 10% for joints and offcuts.
The default 60 tiles per m² is Marley’s figure for its plain tile at a 100mm gauge. Marley advises a minimum pitch of 35° for that tile.
Worked example
A porch roof with a 6 m² plan at 40°: 6 ÷ cos(40°) = 7.8 m² of slope. At 60 plain tiles per m² that’s 470 tiles, or 494 with 5%. Batten: 7.83 ÷ 0.1 = 78m, or 87m with 10% added.
What this doesn’t cover
Ridge, hip and verge tiles, eaves tiles, tile-and-a-half for the verges, underlay and nails are separate. Re-roofing usually needs building regulations approval if more than a quarter of the roof is replaced, so check with building control.
Questions people ask
How many plain tiles per m²?
Marley gives 60 tiles per m² for its plain tile at a 100mm gauge on a roof, and 53 per m² at 115mm on vertical tile hanging.
How do I work out roof area from the floor plan?
Divide the plan area by the cosine of the roof pitch. A 40 m² plan at 35° becomes 40 ÷ 0.819 = 48.8 m² of roof slope. Choose “from plan and pitch” in the calculator to do this for you.
How many interlocking tiles per m²?
It depends on the tile and the headlap, and ranges from under 10 to about 17 per m². Take the figure from the manufacturer’s data sheet for your tile and pitch and type it into the tiles per m² box.
How much tiling batten do I need?
One row per gauge up the slope. Metres of batten = roof area ÷ gauge in metres. At a 100mm gauge that’s 10m of batten per m² of roof.
Sources
Trade review pending. A named tradesperson will check this calculator, and their name and qualifications will appear here.
Figures last checked 25 October 2026. Read how we calculate and our disclaimer. Found a mistake? Tell us.