Roof Area Calculator
Convert a roof footprint and pitch into sloped surface area, roofing squares, and waste-adjusted ordering area.
What this calculator does
A pitched roof covers more surface than its horizontal footprint. This calculator multiplies plan area by the exact pitch multiplier, then shows sloped area and roofing squares.
Roof dimensions
Measure the horizontal footprint. Pitch converts plan area into sloped roof area; waste is applied last.
Your plan updates instantly
Drag with a mouse or finger. Pinch or scroll to zoom.
Plan area x exact pitch slope factor, then waste.
The arithmetic uses the exact values shown above. Verify field measurements, product pack sizes, layout constraints, and local requirements before ordering or building.
How to interpret the result
The result models a simple roof plane. Hips, valleys, dormers, overhangs, openings, and separate roof sections must be measured and added or deducted independently.
How the result is calculated
Slope factor = √(1 + (rise ÷ run)²). Roof area = length x width x slope factor.
Worked example
A 40 x 24 ft footprint at 6:12 pitch has about 1,073 ft² of sloped area before waste.
How to use this calculator
- Measure the building footprint for the roof section.
- Enter rise and run for that section.
- Review sloped area before waste.
- Apply an allowance suited to the actual roof complexity and product instructions.
Supported units
Feet and square feet in imperial mode; meters and square meters in metric mode. Roofing squares equal 100 square feet.
Practical guidance
- Measure the project at least twice before ordering.
- Use actual product dimensions and package coverage.
- Keep a saved or printed copy of the inputs used for the estimate.
Assumptions and limitations
This simple plane model does not add hips, valleys, dormers, openings, or overhangs.
Methodology
Slope factor = √(1 + (rise ÷ run)²). Sloped area = plan length × plan width × slope factor.
Read the complete calculation methodology and testing policy.
Sources and technical references
References support terminology, units, or practical constraints. They do not imply endorsement or project approval.
- NIST Special Publication 811 — Guide for the Use of the International System of UnitsReference for SI units, symbols, and conversion-factor practice.
- U.S. Department of Energy — roof slope terminologyReference for rise-over-run roof slope terminology.
Frequently asked questions
Are results rounded for purchasing?
Countable materials and packages are rounded up. Measured area, length, volume, and cost remain decimal values where appropriate.
Is this a final construction specification?
No. It is a transparent planning estimate. Verify product instructions, site conditions, plans, and local requirements.