Roofing materials calculator
Estimate roof area, roofing squares and bundles from plan size and pitch; a 10 × 8 m plan at 6:12 is about 89 m² or 9.6 squares before waste.
- Runs in your browser
- No upload
- Instant result
Quantity estimate only. This does not approve structural safety, load capacity, drainage, fire resistance or building-code compliance. Verify the design and local requirements with a qualified professional. Purchase quantities round up to whole packs.
Assumptions & formula
Formula and assumptions
w = Waste allowance/100; S=ΣLW√(1+(rise/run)²); Q=S(1+w)/9.290304; N=ceil(Q×b)
Enter horizontal projected roof planes sharing one pitch. Rise/run is a dimensionless slope ratio. A roofing square is exactly 100 ft². Enter manufacturer bundles per square and net underlay coverage after overlap; complex hips and valleys require a separate cut allowance.
The prefilled values are editable examples, not product specifications. Enter your supplier’s yield, density, coverage and packaging values, and add an allowance for overlaps, compaction and cuts where needed.
Purchase counts use the exact entered decimals and unit factors, without a rounding tolerance that could discard a real remainder. π and irrational square roots use enclosing bounds; ambiguous counts produce an error. Counts must be safe integers.
Results
Enter values and press Calculate to see the result here.
How to use this calculator
- Set inputs and units
Enter the horizontal roof plan area and the pitch as rise/run, then add an allowance and the supplier’s coverage per bundle or roll.
- Calculate
Check this worked example: plan=12 m²,pitch=3/4,waste=0%,rollCoverage=10 m²,bundlesPerSquare=3 → roofArea15 m²,rolls2,bundles5
- Results
The slope multiplier converts the horizontal projection to the roof surface. Don't enter a sloped area and then apply the slope a second time.
Questions and limits
What is a roofing square?
Here one square is 100 ft². Bundles per square is an input that depends on the product, not a universal constant.
Which input errors should I correct?
The pitch run and the roll coverage must be positive. Use rise/run in the ratio fields, not an angle in degrees.
What does this calculation leave out?
No valley or ridge layout, flashing, fastener specification, wind loading or roof-access safety design.