Reviewed, sourced guidance
Roofing worked examples: from footprint to order figure
Direct answer
A 10 m by 6 m footprint at 35 degrees gives a 73.2 square metre roof and about 725 tiles at the cited 9.9 per square metre rate, or 798 tiles with a 10 per cent allowance. A two-pitch roof of 61.0 and 13.9 square metres takes about 802 tiles at 10.7 per square metre, or 883 with 10 per cent.
Follow two whole take-offs the way the calculator runs them: pitch conversion, plane areas, product rates, waste allowance and the final order figure.
Key takeaways
- Divide plan area by cos(pitch) to get sloped area.
- Tile rates come from the exact product and headlap.
- Waste is an entered allowance, applied once, then rounded up.
- Every step is checkable by hand against the calculator.
Example one: simple gable at 35 degrees
The plan measures 10 m by 6 m, so the plan area is 60 square metres.
Cosine of 35 degrees is about 0.819, so the sloped area is 60 divided by 0.819, which is about 73.2 square metres.
At the cited rate of 9.9 tiles per square metre (75 mm headlap), the roof needs about 725 tiles before any allowance.
Applying an entered 10 per cent allowance gives 797.5, which rounds up to 798 tiles.
| Step | Working | Result |
|---|---|---|
| Plan area | 10 m x 6 m | 60.0 square metres |
| Sloped area | 60.0 / cos(35 degrees) | about 73.2 square metres |
| Tiles before allowance | 73.2 x 9.9 per square metre | about 725 tiles |
| With 10 per cent allowance | 725 x 1.10, rounded up | 798 tiles |
Sources for this section: Marley, How to calculate roof pitch (observed 2026-09-25)Marley, Duo Modern product data (observed 2026-09-25)
Example two: two pitches, one order
A main roof measures 10 m by 5 m at 35 degrees: 50 divided by 0.819 gives about 61.0 square metres.
A rear extension measures 4 m by 3 m at 30 degrees: 12 divided by 0.866 gives about 13.9 square metres.
The two planes total about 74.9 square metres; at the 100 mm headlap rate of 10.7 tiles per square metre the count is about 802 tiles.
With the same 10 per cent allowance the order figure rounds up to 883 tiles; measure each pitch separately whenever a roof changes slope.
| Plane | Working | Sloped area |
|---|---|---|
| Main roof 35 degrees | 50.0 / 0.819 | about 61.0 square metres |
| Extension 30 degrees | 12.0 / 0.866 | about 13.9 square metres |
| Combined | 61.0 + 13.9 | about 74.9 square metres |
| Tiles before allowance | 74.9 x 10.7 per square metre | about 802 tiles |
| With 10 per cent allowance | 802 x 1.10, rounded up | 883 tiles |
Sources for this section: Marley, How to calculate roof pitch (observed 2026-09-25)Marley, Duo Modern product data (observed 2026-09-25)
From tile count to order figure
Round up once to whole tiles after the allowance, then round again to whole packs as the supplier defines them.
Keep the entered allowance recorded with the take-off so any later quote can be compared on the same basis.
Run the same numbers in the roofing calculator to confirm the hand arithmetic before ordering.
Next steps
- Measure your planes and reproduce these steps with your own numbers.
- Check the product data sheet rate and headlap before converting area into tiles.