How to Find Roof Pitch with a Rafter Square (2 Methods)

Whether you're tying into an existing roof, replacing shingles, or just trying to figure out what you're working with, you need to know the roof pitch. Here are two reliable methods — one from the ground and one with a rafter square on the roof or in the attic.

Method 1: From the Ground (Quick Estimate)

This method gives you a rough pitch without climbing a ladder. It's useful for initial planning, material estimates, and conversations with clients.

Using a Smartphone App

Several free apps use your phone's accelerometer to measure angles. Point the phone's edge along the roof slope from a distance, and the app gives you the angle in degrees. Convert to pitch using this table:

Degrees	Pitch	Degrees	Pitch
4.8°	1/12	30.3°	7/12
9.5°	2/12	33.7°	8/12
14.0°	3/12	36.9°	9/12
18.4°	4/12	39.8°	10/12
22.6°	5/12	42.5°	11/12
26.6°	6/12	45.0°	12/12

Accuracy: Within about 1-2 degrees if you have a clear sightline. Good enough for estimates — not accurate enough for cutting rafters.

Visual Estimation

With experience, you can estimate common pitches by eye:

• Low slope (3/12 - 4/12): Barely noticeable slope. Common on ranch homes, porches, and additions.
• Medium slope (5/12 - 7/12): The "standard" residential look. Most homes fall in this range.
• Steep slope (8/12 - 12/12): Obviously steep. Common on Cape Cods, Colonials, and homes in snowy climates.
• Very steep (over 12/12): Dramatic pitch. A-frames, Gothic styles, and some dormers.

Accuracy: Within 2-3 pitches for an experienced eye. Not reliable for anyone who doesn't see roofs regularly.

Method 2: With a Rafter Square (Precise)

This is the method you use when accuracy matters — for cutting rafters, calculating materials, or matching an existing pitch for an addition.

What You Need

• Rafter square (any type works — a Rapid Rafter, Swanson, Johnson, etc.)
• Torpedo level or small spirit level
• Access to a rafter, either from the attic or on the roof surface

From Inside the Attic

This is the most accurate and safest method.

Step 1: Find an accessible rafter that isn't obstructed by insulation, ductwork, or storage.

Step 2: Place the body of the rafter square against the underside of the rafter, with the fence resting on the top (sloped) edge of the rafter.

Step 3: Hold a torpedo level against the square's body (the long flat edge perpendicular to the fence).

Step 4: Pivot the square until the level reads exactly plumb (bubble centered).

Step 5: Read the pitch. Look at where the rafter's edge crosses the COMMON scale on the square. That number is your pitch. If the edge crosses at "6," you have a 6/12 pitch.

Step 6: Alternatively, read the degree scale for the exact angle. This is useful if the pitch falls between whole numbers.

From the Roof Surface

If you can't access the attic, you can measure from the roof surface.

Step 1: Place the fence of the rafter square on the roof surface (parallel to the slope), with the body extending horizontally.

Step 2: Hold a level along the body of the square (the horizontal leg).

Step 3: Adjust until the level reads true horizontal.

Step 4: Read where the roof surface intersects the common rafter scale.

Safety note: Working on a roof is inherently dangerous. Use proper fall protection, wear appropriate footwear, and never work on a wet or icy roof. If the roof is steep enough that you're uncomfortable standing on it, measure from the attic instead.

From a Gable End Wall

If you can see the gable end (the triangular wall section below the roof peak), you can measure pitch from the ground using a long level and tape measure.

Step 1: Hold a 4-foot level horizontally against the gable wall, starting from where the roofline meets the wall.

Step 2: Level it perfectly.

Step 3: Measure from the far end of the level straight up to the roofline. That vertical distance is the rise over a known run (4 feet / 48 inches).

Step 4: Convert: Rise (in inches) ÷ 4 = pitch per 12" run. For example, if you measure 16 inches of rise over 48 inches, that's 16 ÷ 4 = 4/12 pitch.

Pitch-to-Degree Quick Reference Table

This is the conversion table you'll use most often. Bookmark it.

Pitch	Degrees	Rafter Factor
1/12	4.76°	12.042"
2/12	9.46°	12.166"
3/12	14.04°	12.369"
4/12	18.43°	12.649"
5/12	22.62°	13.000"
6/12	26.57°	13.416"
7/12	30.26°	13.892"
8/12	33.69°	14.422"
9/12	36.87°	15.000"
10/12	39.81°	15.620"
11/12	42.51°	16.279"
12/12	45.00°	16.971"

The Rafter Factor is the rafter length per foot of horizontal run. Multiply your total run (in feet) by this factor to get the rafter length along the slope (in inches).

Example: 10-foot run at 8/12 = 10 × 14.422 = 144.22 inches = 12' 0-1/4"

For the complete reference with hip-valley multipliers and code requirements, see our full Roof Pitch Explained guide.

Why Pitch Matters

Roof pitch isn't just a number — it drives critical decisions:

Roofing Material Selection

Every roofing material has a minimum pitch below which it won't shed water properly:

Material	Minimum Pitch
Asphalt shingles (standard)	4/12
Asphalt shingles (with double underlayment)	2/12
Standing seam metal	1/4:12 to 3/12
Wood shakes	4/12
Slate	4/12
Clay tile	2.5/12

Code Compliance

Building codes set minimum pitches for specific roofing assemblies. A roof that's below the minimum for its material can fail inspection, void warranties, or leak.

Rafter Sizing

Steeper roofs create more lateral thrust at the wall plates, which affects rafter sizing, collar tie placement, and connection hardware. Your structural calculations depend on knowing the exact pitch.

Material Quantities

Steeper pitches mean more roof area per square foot of floor plan. An 8/12 roof has about 20% more surface area than a 4/12 roof over the same footprint — which means 20% more shingles, underlayment, and decking.

Common Pitch Ranges by Roof Style

Roof Style	Typical Pitch Range
Flat / low slope	1/4:12 to 2/12
Ranch / modern	3/12 to 4/12
Standard residential	5/12 to 7/12
Colonial / Cape Cod	8/12 to 10/12
A-frame / steep residential	12/12 to 16/12
Mansard (steep portion)	16/12 to 20/12
Church steeple	20/12+

Most residential roofing falls in the 4/12 to 8/12 range. If you're matching an existing roof, getting the pitch exact is critical — even a half-pitch difference will be visible where the new section meets the old.

What to Do with the Pitch Once You Know It

Once you've measured the pitch, you can:

1. Calculate rafter lengths using the rafter factor table above or a construction calculator
2. Set your rafter square to mark plumb cuts, seat cuts, and birdsmouth layouts
3. Verify roofing material compatibility against minimum pitch requirements
4. Estimate material quantities by calculating true roof area from the floor plan area
5. Communicate with suppliers and inspectors — pitch is the universal language of roof geometry

For the complete reference on all things pitch — including multiplier tables, code requirements, and conversion formulas — see our Roof Pitch Explained guide.