How to Determine Roof Pitch from Inside the Attic

Measuring roof pitch from inside your attic is the safest way to get this critical number. You never have to climb on the roof, and the measurement is just as accurate as an exterior measurement. All you need is a level, a tape measure, and access to an exposed rafter or the underside of the roof sheathing.

Tools Required

• A level (18 inches or longer works best)
• A tape measure
• A flashlight (attics are dark)
• A marker or piece of tape

Step-by-Step Instructions

1. Access the attic: Enter through the attic hatch or pull-down stairs. Be careful to walk only on joists or a plywood walkway, not on the drywall ceiling between joists.
2. Find an exposed rafter: Locate a rafter (the angled framing member running from the ridge to the eave). If rafters are not exposed, you can measure against the underside of the roof sheathing (plywood).
3. Position the level: Hold the level horizontally against the underside of the rafter. Use one end as your starting point.
4. Mark 12 inches on the level: From the end touching the rafter, measure exactly 12 inches along the level and mark that point.
5. Ensure the level is horizontal: Check that the bubble is perfectly centered. This is critical for accuracy.
6. Measure the vertical distance: From your 12-inch mark, measure straight up (vertically) to the underside of the rafter. Use the tape measure perpendicular to the level.
7. Read your pitch: The vertical measurement is the rise. Express the pitch as rise/12. If you measured 5 inches, your pitch is 5/12.

Visual Diagram

    Rafter
     /|
    / |  ← Rise (measure this)
   /  |
  /   |
 /____|
  12"
 Level (horizontal)
        

Tips for Accuracy

• Use a longer level: An 18-inch or 24-inch level gives you a more stable measurement platform than a short torpedo level.
• Measure on the rafter, not the sheathing: Rafters give a cleaner surface. If you must use sheathing, find a spot between nail heads.
• Take multiple measurements: Measure on two or three different rafters and average the results. Slight framing variations can cause a half-inch difference.
• Account for sagging: On older homes, rafters may sag in the middle. Measure near the ridge end for the most accurate original pitch.

What If I Cannot Access the Attic?

If your attic is inaccessible (spray foam insulation, cathedral ceiling, etc.), you have several alternatives:

• Measure from outside the roof: See our exterior roof pitch measurement guide.
• Measure from the gable end: From the ground, photograph the gable end and use the triangle proportions to estimate pitch.
• Check blueprints: Your home's construction plans typically list the roof pitch.
• Use a smartphone app: Hold the phone against a gable rake board or use a photo-based pitch estimator.
• Use our calculator: Our Roof Pitch Calculator can convert between degrees, ratios, and percentages if you have any one measurement.

Common Attic Pitch Measurements

For the complete pitch multiplier table from 0/12 to 24/12, see our Roof Pitch Multiplier Table.

Frequently Asked Questions

Is the attic measurement as accurate as measuring on the roof?

Yes. Both methods measure the same angle — the rafter creates the same slope whether you measure from above or below. The attic method is just as accurate and significantly safer.

What if I get a measurement between whole numbers?

That is normal. If you measure 5.5 inches of rise, your pitch is approximately 5.5/12. For material calculations, round to the nearest whole pitch (6/12 in this case) or use the exact number in our Roof Pitch Calculator, which accepts decimal values.

Can different parts of my roof have different pitches?

Yes. Many homes have a main roof at one pitch and dormers, additions, or porches at different pitches. Measure each distinct roof section separately and calculate their areas independently. Gambrel and mansard roofs have two distinct pitch angles on the same plane.