Free estimate — verify against local code before building
Roof Area Calculator
Get sloped roof area and roofing squares without building a full material list.
What this calculator includes
Estimate actual sloped roof surface from the building footprint, horizontal overhang, and rise-per-12 pitch. The result includes square feet, square meters, roofing squares, and the exact pitch multiplier used.
How to use this roof area calculator
- 01
Measure the wall-line footprint
Enter building length and width as horizontal measurements, not distances measured along the slope.
- 02
Add the overhang
Enter horizontal eave and rake projection. The same overhang is added to all edges in this simplified model.
- 03
Enter pitch
Use inches of rise per 12 inches of horizontal run, such as 6 for a 6-in-12 roof.
- 04
Use the sloped area
Use the square-foot or square-meter result for early planning, or continue to Roofing Materials for package rounding and waste.
Worked example
Example: 36 × 24 ft roof at 4-in-12
With 1-foot overhangs, the plan is 38 × 26 = 988 sq ft. The 4-in-12 pitch multiplier is about 1.054, so the roof surface is about 1,041 sq ft, or 10.41 roofing squares.
Practical buying and overage guidance
Use roof area only for early planning. Before buying, measure each section and opening, separate different slopes, include hips and valleys in layout planning, and apply product-specific waste and package coverage.
Continue the project
Upgrade Roof Drainage
Plan roof area, gutter runs, downspouts, fittings, extensions, drainage stone, grading, excavation, supplies, and contractor pricing.
Open the project workflow →Calculation sources and review
Primary references and formula assumptions are linked so you can verify them against the selected product, supplier, and adopted local requirements.
Internal formula review completed July 13, 2026. What this review covers
- Asphalt Roofing Manufacturers Association — residential roofing (opens in a new tab)
Roofing-square terminology and roof-measurement context.
- NIST — SI unit conversion resources (opens in a new tab)
Square-foot and square-meter conversion reference.
- OSHA — residential construction fall protection (opens in a new tab)
Use safe ground-based, plan-based, or professional measurement methods.
Frequently asked questions
What is a roofing square?
One roofing square is 100 square feet of roof surface. It is an area unit, not a square-shaped section of roof.
Does roof pitch change roof area?
Yes. A steeper roof has more surface area over the same horizontal footprint. The calculator applies a pitch multiplier based on the rise-per-12 slope.
Does this work for hip and shed roofs?
Yes when all planes share one pitch and the roof covers the entered rectangular footprint. Add separate roof sections when pitches or footprint rectangles differ.
Should I measure overhang along the roof?
No. Enter horizontal projection beyond the wall line. The pitch multiplier converts that plan dimension to sloped surface.
Does roof area include material waste?
No. This quick result is geometric area only. Use the Roofing Materials calculator to add waste and round shingles, underlayment, and nails to packages.