Overview
Enter the building length and width, roof pitch, waste percentage, and the coverage per pack, sheet, or roll. The calculator then estimates the actual roof surface and the purchase quantity from that unit coverage. It is most useful when the roof is regular and the product’s coverage is stated clearly on the packaging or technical sheet. That lets you compare tiles, metal sheets, or underlayment using the same roof size and the same allowance for cuts and overlaps. If the roof includes valleys, hips, dormers, offsets, or multiple planes, use the result as a base figure and adjust it for the real layout, trim pieces, and the product’s pack size rules.
Use cases
- Ordering tiles for a houseTurn the roof size into the number of tile packs needed before confirming a supplier order.
- Sizing metal sheetsEstimate how many profiled sheets or panels are needed when each unit has a known coverage area.
- Checking membrane rollsSee whether one roll or several rolls of underlayment will cover the roof with your chosen waste allowance.
- Setting a material budgetBuild a quantity baseline before requesting a quote from a roofer, merchant, or yard.
How it works
- 1
Enter the building length and width in metres.
- 2
Set the roof pitch in degrees.
- 3
Choose a waste percentage for cuts, overlaps, and fitting losses.
- 4
Enter the coverage per pack, sheet, or roll in square metres.
- 5
Review the roof area, area with waste, and the required quantity.
Examples
Family home roof
Input: Length 10 m, width 8 m, pitch 30°, waste 10%, coverage 1.2 m² per pack
Output: Roof area: 92.4 m². With waste: 101.6 m². Packs needed: 85.
Useful when tile coverage per pack is known for a regular home roof.
Workshop sheet order
Input: Length 14 m, width 6.5 m, pitch 22°, waste 7%, coverage 0.85 m² per sheet
Output: Roof area: 72.8 m². With waste: 77.9 m². Sheets needed: 92.
Fits a small workshop or garage roof where sheets are bought by stated coverage.
Membrane roll check
Input: Length 12 m, width 9 m, pitch 35°, waste 12%, coverage 50 m² per roll
Output: Roof area: 132.5 m². With waste: 148.4 m². Rolls needed: 3.
Helps confirm whether two rolls are enough or a third is needed for the full roof.
FAQ
What roof shape does this calculator assume?
It assumes one regular pitched roof setup, such as a straightforward gable roof. Complex intersections need manual adjustment.
Why do pitch and waste both change the result?
Pitch increases the true surface compared with the building footprint, while waste adds material for trimming, overlaps, and installation losses.
How should I enter the coverage value?
Use the manufacturer’s coverage for one pack, sheet, or roll. A net m²-per-unit value gives the most meaningful result.
Why can the quantity seem larger than expected?
A steep roof, small unit coverage, or a high waste allowance can increase the total quickly. Check whether the product is sold per piece, bundle, or full carton.
Can I place an order using only this result?
Use it as a material estimate, then confirm ridge parts, starters, flashings, and the exact packaging format before ordering.