Roofing Calculator
Calculate roof surface area from your building's footprint and pitch, and how many bundles or packages of roofing material you need.
Rise per 12 units of run — e.g. a moderate roof is often 6 in 12.
Check the product packaging for this.
Extra material to cover cuts, mistakes, and offcuts.
Bundles/packages needed
39
How this is calculated
Roof area = footprint area × pitch multiplier (√(144 + rise²) ÷ 12), increased by your extra allowance. Packages needed = that area ÷ coverage per package.
Results are estimates for a simple roof shape. Complex roofs with hips, valleys, and dormers need more material and a higher waste allowance than a straightforward calculation accounts for.
How to measure a roof from the footprint
Measure your building's footprint (length and width from the plan view or eaves), and find your roof's pitch, expressed as rise per 12 units of run. This calculator scales the flat footprint area up to the actual sloped roof surface area.
Then enter the coverage of one bundle or package of your roofing material — usually printed on the packaging — to get a material quantity.
Frequently asked questions
How do I measure roof area from the ground?
Measure your building's footprint (length x width from the plan view, or the eaves), then this calculator scales that flat area up to the sloped roof surface area using your roof's pitch.
What is roof pitch and how do I find mine?
Pitch is expressed as "rise per 12" — how many inches (or any consistent unit) the roof rises for every 12 units of horizontal run. A 6-in-12 pitch is a common moderate slope. Check your building plans, or measure with a level and tape against the actual roof.
How many bundles of shingles do I need?
Divide the roof area (with waste) by the coverage of one bundle — usually printed on the packaging (a "square" is 100 sq ft, and most shingle bundles cover about a third of a square).
How much waste allowance should I use for roofing?
10% is typical for a simple roof. Increase it to 15% or more for complex roofs with lots of hips, valleys, and dormers, which need more cutting.