Roof Square Footage Calculator
Already know your house length, width and roof pitch? Estimate the total roof square footage in seconds.
Inputs
Results
Estimated Roof Square Footage
- House Footprint
- Roofing Squares
What would you like to calculate next?
Enter your house dimensions, then press Calculate.
How to Figure Out Roof Square Footage
To estimate roof square footage (roof sq ft) from the ground or from your floor plan, multiply the house footprint by the pitch multiplier. This is the fastest way to figure out roof square footage without climbing onto the roof.
Watch your measurement basis. Footprint square footage (what this page computes from your building dimensions) is not the same as walkable roof surface — sloped roofs are always bigger. Measure the building's outside walls, add overhang if you shingle them, and apply the pitch multiplier; for the full footprint-vs-surface explanation see the Roof Area Calculator.
Formula
- Footprint = House Length × House Width
- Roof Square Footage = Footprint × √(1 + (Rise / Run)²)
Worked Example
A 40 ft × 30 ft house with a 6/12 pitch: footprint = 1,200 sq ft, multiplier = 1.118, estimated roof square footage ≈ 1,342 sq ft (about 13.4 roofing squares).
What You Need
Two measurements plus the pitch: the length and width of your home's footprint, taken along the outside walls, and the roof pitch. Roof square footage is based on the sloped surface, so the pitch is what converts footprint area into actual roof area.
Assumptions & Limitations
The estimate assumes a simple gable roof over a rectangular footprint and excludes overhang. Complex roofs and garages/porches need separate sections. Results are for planning purposes only.
Frequently Asked Questions
Why is roof square footage larger than my house?
Because the roof surface is tilted. The steeper the pitch, the larger the roof surface compared to the footprint.
How accurate is this estimate?
For simple rectangular roofs it is close. For roofs with hips, valleys and dormers, expect the real area to be somewhat higher — add a waste allowance when ordering materials.
Related Calculators
Roof Area Calculator
Calculate your roof surface area from footprint length, width and roof pitch. Free online roof area calculator with pitch multiplier.
Roofing Squares Calculator
Convert roof square feet to roofing squares, with waste adjustment. One roofing square = 100 square feet. Free calculator.
Sources & Methodology
- International Residential Code (IRC) — Chapter 9, Roof Assemblies — minimum roof slope, roof covering and flashing requirements for one- and two-family dwellings
- NRCA — National Roofing Contractors Association, Roofing Manual: Steep-slope Roof Systems — industry-standard roof geometry, roofing square and installation conventions
Formulas, assumptions and rounding rules: Methodology · Last updated: September 2026 · Calculation Engine: p1-v1 · Published by the RoofCalcWorks Editorial Team.