Roof tile calculator
Estimate developed roof area from building footprint and pitch, then calculate roof tiles and packs with a cutting and breakage allowance.
Roof tile quantities
Enter the building footprint, pitch and tile coverage. The calculator corrects horizontal area for the roof slope.
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How does this tool work?
A pitched roof always covers more than the building footprint: at 35°, an 80 m² footprint becomes almost 98 m² of roofing. This calculator takes the footprint length and width, overhangs included, corrects that area for the pitch, then converts it into field tiles and packs using the coverage per m² of the chosen tile. It also shows the ridge length so you can order ridge tiles.
Projected area is building length × width. For slopes of equal pitch, the actual roof area is that footprint divided by the cosine of the angle: the factor is about 1.15 at 30°, 1.22 at 35° and 1.41 at 45°.
The theoretical tile count multiplies the roof area by the manufacturer’s tiles per m², which depends on the gauge and headlap of the model. The cutting and breakage allowance is added, the total is rounded up to the next tile and divided by tiles per pack, rounded up to the next pack.
The ridge length shown equals the building length: this is the case for a dual-pitch roof whose ridge runs along the longer side.
Limits: pitch is entered in degrees, not percent; a 35% slope is only about 19°. Hips, valleys, dormers and slopes with different pitches must be calculated slope by slope. Ridge tiles, verge tiles, vent tiles, eaves fillers and battens are not counted. Minimum pitches and fixing rules (BS 5534 in the UK, NF DTU 40.2 series in France, manufacturer data elsewhere) remain references to check: the tool does not check the roof structure or whether the tile suits your exposure zone.
Roof tiles are estimated from the sloping roof area, not just the horizontal footprint. Tiles per square metre depend on gauge and the selected model, so use manufacturer data before converting area into pieces.
How to use this tool
Measure the roof footprint
Enter length and width at eaves level, overhangs included, not the internal dimensions of the house.
Enter the pitch in degrees
Take the angle from the drawings or measure it; if you only know the slope in percent, convert it to degrees first.
Use the tile data sheet
Enter the tiles per m² and tiles per pack stated for the model you have chosen.
Adjust the allowance and read the order
Keep about 8% for a simple roof, more with valleys and hips, then note tiles, packs and ridge length.
Sloped area and tile count
The roof is larger than its footprint by a factor that depends on the pitch.
Roof area
A = L × W ÷ cos α
L × W is the horizontal footprint, overhangs included.
Tiles to order
N = ⌈A × n × (1 + allowance)⌉
n is the number of tiles per m² for the model.
Packs
P = ⌈N ÷ tiles per pack⌉
q is the number of tiles per pack or pallet.
The formula assumes roof slopes with the same pitch. Hips and valleys are calculated slope by slope, and fittings are ordered separately.
Use cases
Re-roofing a house
Estimate the tiles for a 10 × 8 m dual-pitch roof before asking for quotes or comparing prices per m².
Choosing between two tile models
Compare a large interlocking tile at 10 per m² with a small plain tile at more than 20 per m² on the same roof.
Seeing the effect of pitch
Find out how much area, how many tiles and packs a 45° pitch adds compared with 30°.
Examples
10 × 8 m house at 35°
80 ÷ cos 35° = 97.66 m². At 10 tiles/m² plus an 8% allowance, that makes 1,055 tiles.
Input
Footprint 10 × 8 m, pitch 35°, 10 tiles/m², 5 tiles per pack, 8% allowanceResult
80 m² footprint, 97.66 m² of roof, 977 theoretical tiles, 1,055 to order, 211 packs, 10 m ridge12 × 9 m roof at 45° with small tiles
At 45° the sloped area is about 1.41 times the footprint; a small tile nearly doubles the count per m².
Input
Footprint 12 × 9 m, pitch 45°, 22 tiles/m², 20 tiles per pack, 8% allowanceResult
108 m² footprint, 152.74 m² of roof, 3,360 theoretical tiles, 3,629 to order, 182 packs, 12 m ridgeTips and best practices
- Coverage per m² changes with the gauge: the same tile laid at a shorter gauge on a low pitch needs more pieces per m².
- For a hipped roof, use the total footprint if all slopes share the same pitch, but count the hips separately, as they need cuts and fittings.
- Order a few spare packs from the same batch: a discontinued model or a colour change makes later replacements difficult.
- Use the ridge length to order ridge tiles according to the number per linear metre given by the manufacturer.
Sources and references
Frequently asked questions
Why is the roof area larger than the footprint?
A sloping surface is longer than its horizontal projection. The factor depends on the pitch.
Does the calculation work for a hipped roof?
It gives an order of magnitude if the whole roof has the same pitch and the horizontal footprint is entered correctly. Complex shapes should be split into simpler parts.
Is the number of tiles a final order quantity?
No. Use the manufacturer’s consumption and instructions, then add the accessories and constraints specific to the job.
How many tiles per square metre?
It depends on the model and gauge: large interlocking tiles are often laid at around 10 to 15 per m², small plain tiles at far more. Always use the per-m² figure from the manufacturer’s data sheet.
What is the minimum pitch for a tiled roof?
Each tile model has a minimum pitch that varies with climate zone, exposure and rafter length. Check it in the manufacturer’s literature before choosing the tile.
Are ridge and verge tiles included?
No, the calculation covers general field tiles. The ridge length shown lets you order ridge tiles from the number per metre given by the manufacturer; add verges, vents and other fittings too.
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