Roof Square Footage Calculator
This calculator finds true roof area from building length, width, pitch, roof type, and overhang, using roofArea = footprintArea × slope factor, with overhang added to the footprint on all four sides before the slope correction is applied.
History
Saved
No saved results yet. Use "Save this result" to pin one.
Recent
No recent results yet. Copy or print a result to see it here.
Scenario presets
- Footprint area (incl. overhang)
- 1,092 sq ft
- Squares (100 sq ft units)
- 12.21
- Area per roof plane
- 610 sq ft
- Slope factor
- 1.118
How it works
The footprint is a flat, top-down rectangle. The roof surface sits on top of it at an angle, so it covers more actual area than the flat footprint suggests — exactly how much more depends on the pitch.
roofArea = (length + 2×overhang) × (width + 2×overhang) × slopeFactor
- Footprint — outside wall length × width, plus overhang added to all four sides.
- Slope factor — √(144 + pitch²) ÷ 12, the same correction used by the Rafter Length and Roof Slope Calculators.
- Area per plane — total roof area divided across each slope (2 for gable, 4 for hip, 1 for shed) — an even split, useful for ordering material per side.
Worked example
A 40 ft × 24 ft ranch house, 6/12 pitch, 12" overhang, gable roof.
Effective footprint. Overhang adds 1 ft to each side: (40 + 2) × (24 + 2) = 42 × 26 = 1,092 sq ft.
Slope factor. √(144 + 36) ÷ 12 = 1.118 (6/12 pitch).
Roof area. 1,092 × 1.118 = 1,220.8 sq ft, or 12.2 squares.
Per plane. A gable roof splits into 2 slopes: 1,220.8 ÷ 2 = 610.4 sq ft per side.
Tips from the field
- Measure the footprint at the outside wall line, not the foundation or the roofline — overhang is added separately.
- Confirm pitch on-site with a speed square rather than trusting a plan set that may predate a re-roof.
- For a roof with more than one pitch or an irregular footprint, use the Roof Area Calculator to sum individual sections instead of forcing one pitch across the whole building.
- Round up to the next full square when ordering — shingle and metal packaging is sold by the bundle or panel, not by the exact square foot.
What this tool does not do
- Does not handle irregular footprints or multiple pitches — use the Roof Area Calculator for that.
- Does not calculate material quantities — feed the resulting area into the Shingle, Metal Roof, or Squares of Shingles Calculator.
- Does not subtract chimneys, skylights, or other roof penetrations.
For multi-section or irregular roofs, see the Roof Area Calculator. To convert this area straight into shingle bundles, see the Shingle Calculator.
Did this calculator help you?
Thanks for the feedback.
Frequently asked questions
These are the questions that come up when a footprint measurement from a plan set needs to become a real roofing material order.
Why is roof area always bigger than the building footprint?
Because the roof surface is sloped, not flat. The footprint is a flat, top-down measurement; the roof area accounts for the actual sloped surface, which is always longer than its flat projection at any pitch above 0/12.
Does overhang really add that much to the total area?
It adds more than most people expect, because overhang extends on all four sides of the building, and each added foot of overhang adds a full ring around the perimeter — not just a strip on one edge.
What counts as the footprint — inside or outside wall measurement?
Use the outside wall dimensions. Roofing overhangs the walls, so measuring to the inside faces would understate the actual roof coverage needed.
How does roof type (gable, hip, shed) change the area calculation?
For a given footprint and pitch, gable and hip roofs cover approximately the same total surface area — the footprint-times-slope-factor method is a standard estimating approximation for both. A shed roof has no ridge, so its footprint isn't split between two slopes; it's treated as one single sloped plane.
Is the hip roof approximation accurate enough to order materials?
It is accurate enough for planning and typical material ordering, which is why estimators use it. For a precise take-off on a complex hip roof with multiple ridge heights, a section-by-section measurement (see the Roof Area Calculator) is more exact.
What is a "square" in roofing, and why does the result show it?
A square equals 100 square feet of roof surface — the standard unit roofing materials are ordered in. Squares = roof area ÷ 100.
How is "area per plane" useful?
It tells you how much material each individual roof slope needs — useful when ordering by the pallet or when one slope faces a different direction and needs a different color or product run.
Can I use satellite or drone measurements for the footprint?
Yes, as a starting point — but confirm the pitch on-site. Aerial measurement services are good at footprint dimensions but sometimes estimate pitch, which is the number that has the largest effect on the final roof area.
Does this calculator account for dormers, chimneys, or skylights?
No — it calculates a clean rectangular footprint. Subtract cutout areas (chimneys, skylights) and add dormer surface area separately, or use the Roof Area Calculator to sum irregular sections.
Why does my contractor's number differ slightly from this calculator?
Contractors often round up for waste, add a percentage for cutting complexity on hip and valley roofs, or measure from an as-built survey rather than plan dimensions. This tool gives the clean geometric area; material calculators add waste factors on top of it.
What pitch should I use if my roof has more than one slope?
Calculate each differently-pitched section separately with the Roof Area Calculator and add the results — averaging pitches before calculating area will give an incorrect total.
How accurate does my footprint measurement need to be?
Within an inch or two is plenty for material ordering. Small footprint errors have much less effect on the final material quantity than an incorrect pitch does.
How we checked this page
- Written by
- Pitch & Span Editorial
- Reviewed by
- Formula checked against the slope-factor geometry used across the site's rafter and slope calculators; the gable/hip footprint-times-slope-factor method is a standard roofing estimation approximation.
- Last reviewed
- 2026-07-28
- Publisher
- Pitch & Span
- Scope
- Roof area estimation from building footprint
- What we checked
-
- Worked example (40 x 24 ft, 6/12, 12" overhang) verified against the live calculator.
- Overhang confirmed to apply to all four sides of the footprint before the slope correction.
- Slope factor cross-checked against the Rafter Length and Roof Slope Calculators for consistency.
Cite this calculator
Pitch & Span. "Roof Square Footage Calculator." Pitch & Span, https://pitchandspan.com/roof-square-footage-calculator/. Accessed .
Related tools
- Rafter Length Calculator
Rafter run, rise, length, and cut angles from span, pitch, and overhang.
- Shingle Calculator
Bundles, squares, and nails from roof area, exposure, and waste factor.
- Metal Roof Calculator
Panel count, panel length, and fasteners for standing-seam and corrugated metal.
- Board Foot Calculator
Board feet and cost from thickness, width, length, and quantity.
- Birdsmouth Cut Calculator
Seat cut, heel plumb, and heel height above plate for a birdsmouth notch.
- Roof Replacement Cost Calculator
Total and per-square cost range by material, tear-off, and complexity.
- Squares of Shingles Calculator
Converts roof area to squares (100 sq ft units) for material ordering.
- Roof Area Calculator
Sums multiple roof sections of different shapes into one total area.
- Joist Span Calculator
Maximum allowable joist span from published span tables by species, grade, and load.
- Roof Pitch Calculator
Converts between x/12 pitch, degrees, and percent slope.
- Roof Slope Calculator
Slope factor and correction multiplier for any pitch from 1/12 to 24/12.
- Roofing Calculator
Hub calculator: area, materials, and cost in one pass, linking to every specialized tool.
Comments and suggestions
Found a bug, have a suggestion, or just want to say hi? Post it below.
- No comments yet — be the first.