Roofing calculator
Enter the plan length and width, the pitch and the tile type, and the calculator returns the true roof area, tile count, batten length and underlay rolls. Add hips, ridges and verges on the quote as linear items.
Roof dimensions
Tile type
Pricing the job? Open EstiMate free and these quantities go straight onto the materials list with your prices.
How it works out the quantities
- 1Roof (slope) area = plan area ÷ cos(pitch). A 30° pitch adds about 15% to the plan area; 45° adds about 41%.
- 2Tiles per m² depend on the tile and gauge — large-format interlocking around 10 per m², plain tiles about 60 per m², natural slate (500 × 250) about 20 per m².
- 3Battens: roof area ÷ gauge gives linear metres (a 345 mm gauge needs about 2.9 m of batten per m²).
- 4Underlay rolls from the roof area plus laps; waste of 5–10% covers cuts at hips, valleys and verges.
Site tips before you order
- Measure the plan from the gutter line, not the wall — include the overhang.
- Ridge, hip and verge tiles, dry-fix kits and ventilation are counted by the linear metre and added on the quote.
- Allow for stripping and disposal (skip tonnage) and scaffold on every re-roof.
- Check the manufacturer's minimum pitch for the tile you're quoting.
Common questions
How do I work out roof area from the plan size?
Multiply the plan area by 1 ÷ cos(pitch): ×1.15 at 30°, ×1.22 at 35°, ×1.31 at 40°, ×1.41 at 45°. The calculator does it from the pitch you enter.
How many roof tiles per m²?
About 10 for large interlocking concrete tiles, 16–17 for smaller interlocking, around 60 for plain clay tiles and 20 for standard natural slates — the gauge changes it, so check the datasheet.
How much batten per m²?
Roof area ÷ batten gauge: about 2.9 m per m² at a 345 mm gauge, 3.3 m at 300 mm.
How many rolls of underlay?
A typical 1 m × 50 m roll covers about 45 m² after 150 mm laps; the calculator rounds up from your roof area.
Related calculators
Concrete & screed calculator
Enter the length, width and depth of the pour and choose the mix. The calculator returns the volume in cubic m…
Brickwork & blockwork calculator
Give the wall length and height (or the area), pick brick or block and the bond, and get the number of units, …
Sand & cement mortar calculator
Pick the ratio and tell it the wall area or the mortar volume you need. It returns 25 kg cement bags and sand …
Quantities are half the quote. EstiMate does the other half.
Drop the numbers into a priced, branded quote your client can accept online — free for your first three jobs a month.
Try EstiMate freeNo credit card · Free plan always available · Cancel anytime