About this calculator
This calculator counts interlocking concrete or clay roof tiles for a symmetric two-slope (gable) roof: how many courses (rows) and columns each slope needs, the tiles to buy with a waste allowance, the tiles per m², the ridge tiles, optional left- and right-hand verge tiles and the tile clips.
Two product figures decide everything. The effective cover width is how much of the roof one tile covers across the slope once it interlocks with its neighbour — less than the tile's own width. The batten gauge is the distance between battens, i.e. how much of the slope one course covers; the manufacturer gives a minimum and maximum gauge for the tile (it depends on the headlap the tile needs, which in turn depends on the pitch). You choose the gauge inside that range.
The building is described exactly as in the gable roof and roof sheets calculators: the building length along the ridge, the span wall to wall, the gable overhang at each end and the horizontal eaves overhang. The pitch is an angle or a rise per run; or you can enter the slope length directly.
Formula
roof length = building length + 2 × gable overhang
slope length = given, or (span / 2 + eaves overhang) / cos(pitch)
tiled length = slope length + eaves tile projection
courses per slope = ceil(tiled length / gauge)
columns per slope = ceil((roof length − 2 × verge tile cover) / cover width)
field tiles (net) = 2 × courses × columns
waste = ceil(net × waste %)
tiles per m² = 1 m² / (cover width × gauge)
ridge tiles = ceil(roof length / ridge tile effective length)
verge tiles = 2 × courses left-hand + 2 × courses right-hand (if used)
clips = ceil(net × clipped %) × clips per tile
Every count rounds up. The batten count itself is not repeated here: use the roof battens calculator with the same gauge.
Worked example
A 10 m building with 300 mm gable overhangs, a 5 m slope, tiles projecting 50 mm past the eaves edge, a 300 mm cover width, gauge range 312–345 mm, 330 mm gauge used, 5 % waste, 420 mm ridge tiles, every tile clipped:
roof length = 10 000 + 2 × 300 = 10 600 mm
tiled length = 5000 + 50 = 5050 mm
courses = ceil(5050 / 330) = ceil(15.30) = 16
columns = ceil(10 600 / 300) = ceil(35.3) = 36
field tiles = 2 × 16 × 36 = 1152
waste 5 % = ceil(57.6) = 58 → 1210 to buy
tiles per m² = 1 / (0.30 × 0.33) = 10.10
ridge tiles = ceil(10 600 / 420) = 26
clips = 1152 × 1 = 1152
The 10.10 tiles/m² matches the manufacturer's own 9.7–10.7 per m² for a 300 mm tile laid at 345–312 mm gauge.
FAQ
Where do I find the cover width and the gauge range? In the tile manufacturer's technical data sheet. It usually lists the cover width, the minimum and maximum batten gauge (often depending on the pitch) and the consumption per m². The defaults here are typical figures for a large-format concrete tile and must be replaced with your product's.
Why does the calculator show tiles per m²? Because that is how manufacturers quote consumption: one square metre divided by the area one tile covers (cover width × gauge). Comparing it with the data sheet is a quick check that the cover width and gauge you entered are right.
Why is the waste not applied to ridge and verge tiles? They are counted per piece along a known length, and spares are usually bought individually. Add a spare or two yourself if you want them.
Are battens, underlay and eaves accessories included? No. Battens and counter-battens are in the roof battens calculator; the breathable membrane is in the roof underlay calculator. Eaves vents, valley trays, hip tiles, ventilation tiles and flashings are not counted.
How many tiles need clips? That depends on the wind zone, pitch, building height and the roof zone (edges and corners need more), and the manufacturer publishes the fixing schedule. Enter the share of tiles to be clipped; the default of 100 % is a conservative placeholder.
Assumptions and limits
No standard is cited. EN 490 (concrete roofing tiles) and EN 1304 (clay roofing tiles) are product standards: they cover the tile's dimensions, tolerances and tests, not how many tiles a roof needs, the gauge or the fixing schedule. The take-off itself is geometry and counting.
All product figures are defaults to replace: the 300 mm cover width, the 312–345 mm gauge range and 330 mm gauge, the 420 mm ridge tile, the verge tile cover width, the 50 mm eaves projection, the 100 % clipping and the 5 % waste.
The roof is a symmetric gable: no hips, valleys, dormers or roof windows. The courses are counted from the eaves tile's lower edge to the ridge centreline, and the top course is rounded up to a whole course. If spreading the courses evenly would need a gauge below the product minimum, the calculator warns you.
Columns are rounded up; in practice the layout is shifted so whole tiles finish at both verges, and the calculator reports how much the last column runs over.