Roof Measurements: How to Measure a Roof, 5 Methods from Ground Tape to Drone

Last reviewed: October 2026.

Roof measurements come from five methods: ground tape and footprint math, measuring from inside the attic, satellite reports from Google Earth Pro or EagleView, a pitch gauge plus footprint math, and direct rooftop tape. Every method except direct rooftop tape ends at the same equation: projected footprint x pitch multiplier (1.118 at 6/12) = sloped roof area. Contractors commonly start a bid from an aerial report and verify on the roof at tear-off, while a homeowner checking a quote can trace the roof in Google Earth Pro and add a pitch reading. The accuracy percentages in the method headings are rule-of-thumb ranges, not measured results. Related: the calculator method.

The math (formula)

Every method except direct rooftop tape ends at the same equation. Related: Roof size calculator method. You need projected area (the horizontal footprint of what the roof covers) and pitch (rise over run); at 6/12 the multiplier is 1.118, so 2,709 sq ft of projected area becomes 3,029 sq ft of roof.

Direct rooftop measurement skips the pitch multiplier because you are measuring the actual sloped surface. For the full data set, see the 2026 Aerial Roof Measurement Software Report. Every other method gives you projected area, which has to be converted. The conversion table below has the multipliers for every standard pitch.

Conversion table: pitch to multiplier

Pitch (rise/run)	Pitch multiplier	Degrees	For a 2,400 sq ft footprint
2/12	1.014	9.5	2,434 sq ft
4/12	1.054	18.4	2,530 sq ft
5/12	1.083	22.6	2,599 sq ft
6/12	1.118	26.6	2,683 sq ft
7/12	1.158	30.3	2,779 sq ft
8/12	1.202	33.7	2,885 sq ft
9/12	1.250	36.9	3,000 sq ft
10/12	1.302	39.8	3,125 sq ft
12/12	1.414	45.0	3,394 sq ft

Worked example: 2,400 sq ft ranch with 6/12 pitch

Four of the methods, run on the same house (a 40 ft x 60 ft ranch with a 6/12 pitch and an 18 inch eave overhang under a simple gable roof), should return these calculated figures; they are illustrations, not field measurements.

Method 1 (ground tape): measure the exterior walls. 40 ft x 60 ft = 2,400 sq ft. Add the overhang: (40 + 3) x (60 + 3) = 2,709 sq ft. Multiply by 1.118 = 3,029 sq ft. The 6/12 pitch comes from a smartphone app or a level-and-tape estimate from the gable end.

Method 2 (Google Earth Pro): trace the roof outline including the overhang. The projected area should read about 2,709 sq ft; x 1.118 = 3,029 sq ft.

Method 3 (aerial report): a report for this house should show about 3,029 sq ft of roof surface in 2 planes of roughly 1,515 sq ft each.

Method 4 (direct rooftop): each plane is 63 ft along the eave by a sloped rafter run of 21.5 ft x 1.118 = 24.04 ft, so 63 x 24.04 = 1,515 sq ft per plane and 3,029 sq ft for both.

All four methods land on the same 3,029 sq ft because they use the same geometry; real measurements will scatter around it, and a gap of more than 5% is a reason to re-measure. 3,029 sq ft is 30.29 squares. Apply 7% gable waste: 30.29 x 1.07 = 32.4, so 33 squares of shingles to order (99 bundles). For the full worked math on turning square footage into a bundle count, see how to estimate the shingle bundles needed. The same workflow drives our how to calculate roof square footage guide.

Method 1: ground tape estimate (free, ~10% accuracy)

The cheapest and most homeowner-friendly approach. Walk the perimeter of the house with a 100 ft tape, measure the exterior wall lengths, multiply length x width to get the footprint (see our roof area vs footprint method), add the overhang, then multiply by the pitch multiplier.

What you need

• 100 ft tape measure (a 25 ft tape will produce too many segment errors)
• A helper to hold one end
• A pitch estimate (from a smartphone app or a level-and-tape from the gable)
• Paper and pen for sketching

What this method misses

• Overhangs vary by elevation (front vs back, eave vs rake). Measure several to get an average.
• Attached garages or porches with different pitch need separate calculation.
• Bump-outs and bay windows can change the footprint.
• Dormers add area not visible in the ground footprint.

Accuracy: 8% to 12% on a simple roof, 15% on a complex one. Good enough to sanity-check a contractor’s quote, not good enough to order shingles (see our how to measure a roof for shingles guide).

Method 2: attic from inside (free, ~15% accuracy)

Useful if the house is two stories and you cannot easily measure the footprint from outside. From inside the attic, measure the rafter run (eave to ridge) and the ridge length. Multiply by 2 for a gable roof to get total sloped surface area. This gives you the actual sloped area, no pitch multiplier needed: a 24 ft rafter under a 63 ft ridge is 1,512 sq ft per plane, or 3,024 sq ft for the gable.

The attic workflow

1. Find the longest unbroken rafter from eave to ridge.
2. Measure that rafter length (the slope of the roof above).
3. Measure the length of the ridge from inside.
4. Multiply: rafter length x ridge length = area of one plane.
5. Multiply by 2 for a gable, by 4 for a hip (planes will be triangular, calculate separately).

The attic method is harder than it sounds because attics are dark, insulation gets in the way, and the rafter is rarely a clean straight line you can pull a tape across. Use a laser distance measurer such as the Bosch GLM 50 C instead of a tape. Accuracy: 10% to 15% if you can get clean measurements.

Method 3: satellite reports (EagleView, GAF QuickMeasure, Hover, Google Earth Pro)

Aerial reports are the usual starting point for contractor bids. There are two tiers: paid commercial reports (EagleView, Hover, GAF QuickMeasure, Roofr) and free DIY (Google Earth Pro).

Paid commercial reports

• EagleView: reports break out every plane, ridge, valley, hip, eave, and rake (ridge and valley lengths drive the ridge cap and ice-and-water orders). It is sold mainly through contractors and insurers, so the practical route for a homeowner is to ask the contractor to share the PDF.
• Hover: photo-based measurement and 3D models. Its pricing page (checked October 2026) lists contractor plans at $999 and $2,999 per year; look there for per-project report pricing.
• GAF QuickMeasure: a measurement report offered through GAF to contractors; confirm eligibility and cost with GAF.
• Roofr: bundles measurement reports with quoting software for contractors.

For homeowners, the cleanest workflow is to ask the contractor to share the EagleView PDF as part of the quote. Reputable contractors will. If the contractor refuses, order a Hover report yourself and compare.

Google Earth Pro (free)

Google Earth Pro is the free desktop application that traces polygons on satellite imagery and outputs area in square feet. Accuracy depends on imagery resolution and capture date, so check both before trusting an outline.

1. Download Google Earth Pro (desktop, not the browser version).
2. Search your address.
3. Click the polygon tool.
4. Set the dialog to measure in square feet.
5. Trace each roof plane by clicking each corner.
6. Read the area in the dialog.
7. Repeat for every plane and sum.
8. Multiply by the pitch multiplier (Google Earth measures projected, not sloped).

Method 4: pitch gauge plus footprint (smartphone era)

The pitch is half the measurement. Once you have it, the footprint method becomes accurate to within 5%. Smartphone apps in 2026 make pitch measurement trivial.

The pitch tool options

• Pitch Gauge app: hold the phone against any sloped surface, read pitch in rise/run, degrees, and percent.
• Roofr app: pitch measurement plus satellite measurement.
• Smart Tool Pitch Locator (physical tool): a magnetic level with a pitch dial. Stick to any steel rafter or roof deck and read directly.
• Bosch GAM 220 MF Digital Angle Finder: digital readout, useful for steeper pitches where reading a dial is awkward.
• Level and tape (old school): hold a 12 inch level against the rake, measure how far the eave-end of the level is from the roof surface in inches. That number is the rise. Rise over 12 = pitch.

For homeowners staying off the roof, hold a smartphone running Pitch Gauge against a gable rake board from a ladder. Pitch measurement does not require walking the roof. The full method is in our how to calculate roof pitch guide.

Method 5: direct rooftop measurement (most accurate, only for harnessed pros)

The ground truth method. Walk the roof, measure each plane with a 50 or 100 foot tape (or a laser distance measurer), and sum. No pitch multiplier needed because you are measuring the actual sloped surface.

The rooftop workflow

1. Set up fall protection: a harness anchored to a ridge anchor, a roof ladder on steeper pitches, and a spotter on the ground. For crews, OSHA’s residential rule applies at 6 feet or more above a lower level (29 CFR 1926.501(b)(13)).
2. Sketch the roof: number each plane.
3. For each plane, measure the eave length and the rake length. Area = eave x rake for a rectangular plane.
4. For triangular planes (hip ends), area = 1/2 x base x height.
5. For trapezoidal planes (hip sides), area = 1/2 x (sum of parallel sides) x height.
6. Sum all planes for total roof area.

This method is only sensible for trained roofers with proper fall protection. A homeowner climbing a steep roof without a harness is gambling for marginal accuracy gain over what Google Earth Pro can deliver from the desk. Related: Roof safety harness.

How roof shape changes the measurement workflow

Roof type	Planes to measure	Easiest method
Gable roof	2 rectangles	Footprint x pitch multiplier (most accurate of free methods)
Hip roof	4 planes: 2 trapezoids, 2 triangles	Footprint x pitch multiplier still works for total area
Gambrel roof	4 planes: 2 steep + 2 shallow	Calculate each pitch zone separately and sum
Mansard roof	8 planes: 4 steep + 4 shallow	Satellite report only practical option
Hip with dormers	4 main + 3 per dormer	Satellite report or direct measurement
Complex cut-up	10+ planes	EagleView is the only practical option

What homeowners should do (and when)

If you need to	Then
Sanity-check a quote	Trace the roof in Google Earth Pro, multiply by the pitch multiplier, and compare with the bid; a gap above 5% is worth a question.
Get a second opinion before signing	Order a Hover report and compare it with the contractor’s report.
Measure a two-story house you cannot walk	Use the attic method or an aerial report instead of the ground footprint.
Measure a mansard or a cut-up roof with 10+ planes	Use an aerial report; hand math is impractical.
Work above 6 feet on a roof	Hire a trained crew; fall protection applies (29 CFR 1926.501(b)(13)).

For a garage or outbuilding you are re-roofing yourself, measure directly on the deck after tear-off: a 20 ft x 12 ft garage plane is 240 sq ft, and no multiplier is needed because you are taping the sloped surface.

For an insurance claim: the insurance adjuster typically writes the estimate in Xactimate, Xactware’s estimating software, so ask which measurement source and pitch the adjuster used and request a copy of the measurement report.

What contractors should do

Start each bid from an aerial report such as EagleView or GAF QuickMeasure, and treat the report fee as a bid overhead item. Verify on the roof during tear-off, because aerial reports can miss tree-covered planes, recently added structures, and subtle pitch changes.

Common measurement mistakes

• Confusing the house’s interior square footage with the roof footprint. Two-story homes have half the footprint of their living square footage.
• Forgetting the overhang. An 18 inch overhang adds 3 ft to length and width, which on a 40 x 60 house adds 309 sq ft of footprint before pitch multiplier.
• Using the wrong pitch multiplier. A 6/12 multiplier (1.118) on a 9/12 roof (1.250) underestimates area by about 11%.
• Forgetting waste. Order quantity is roof area x (1 + waste factor), not just roof area.
• Counting only the main roof on a house with an attached garage or porch with separate pitches.

FAQ

Can I measure my roof from Google Maps instead of Google Earth Pro?

Google Maps does not have the polygon-area tool. Google Earth Pro (a separate free download) does. Use Google Earth Pro.

How accurate are smartphone pitch apps in 2026?

Usually within about a degree on a clean surface once the phone is calibrated on a known level surface, which is close enough: 6/12 is 26.57 degrees, and 27.57 degrees reads as 6.26/12, a quarter inch of rise. Pitch Gauge, Roofr, and the iOS Measure app all use the phone’s accelerometer. Accuracy drops if the surface has roofing material that adds bumps (such as architectural shingles), so measure against the rake board or a roof deck if possible.

Does the satellite imagery in EagleView account for snow or shadow?

Imagery capture dates vary by location and provider, so check the date on the report before relying on it. Tree canopy can hide a plane, and a plane the software cannot see has to be estimated, so ask the contractor to confirm those planes on the roof and to state the imagery date in the quote.

How do I measure a flat or low-slope roof?

Low-slope roofs (below 2/12) have a pitch multiplier of 1.014 or less (1.014 at 2/12), so footprint = roof area for practical purposes: a 30 ft x 40 ft flat roof is 1,200 sq ft. Measure the perimeter, calculate area, and you are done. Membrane systems such as TPO and EPDM are rolled rather than cut like shingles, so check the manufacturer’s coverage per roll for the waste allowance.

Should I measure before or after tear-off?

Bid measurement happens before tear-off, ahead of any 31-square material order. Verification after tear-off is sometimes useful for change-order discussions if hidden damage requires new sheathing. The measured area itself does not change.

Bottom line

Five methods, four pitch multipliers to memorize (4/12 = 1.054, 6/12 = 1.118, 8/12 = 1.202, 12/12 = 1.414), one formula (projected footprint x pitch multiplier = sloped roof area), and one waste factor (7% to 15%). Homeowners can use Google Earth Pro plus a Pitch Gauge app for sanity-checking quotes. Contractors commonly start bids from EagleView or GAF QuickMeasure and verify with a roof walk during tear-off. Most measurement disagreements between homeowner and contractor come down to the waste factor and the overhang, not the underlying roof surface. Run the math twice, ask to see the contractor’s source, and trust the formula.