What tools gauge roof pitch, and how do you use them?
Short answer. Roof pitch gauges include bubble style pitch gauges that read x/12 directly, magnetic angle locators, digital angle finders, speed squares, and phone inclinometer apps. Set the tool on a rafter or the roof surface, read the pitch or angle, and convert degrees to x/12 if needed.
Types of pitch gauges
- Bubble pitch gauge: a flat tool with a vial and a scale marked in rise per 12. Lay it on the roof or a rafter and read the pitch directly. Simple and inexpensive.
- Magnetic angle locator: a dial that reads degrees, often with a magnetic base for metal surfaces. Convert degrees to pitch afterward.
- Digital angle finder: displays degrees to a tenth, and some models show pitch or percent too.
- Speed square: a framing tool with a common rafter scale that reads pitch when used with a level.
- Phone apps: use the phone's built in sensors. Good for a quick read, but calibrate on a known level surface first.
- Sighting pitch finders: some gauges let you line up the roof edge from the ground; accuracy is rougher.
Getting an accurate reading
- Measure on a rafter or rake board when possible. Shingles are uneven, especially laminated ones.
- Take readings in two or three spots and average them.
- Keep the tool square to the slope, not angled across it.
- Recheck after setting the tool down to make sure it did not slide.
Reading degrees as pitch
- 14.0 degrees: 3/12
- 18.4 degrees: 4/12
- 26.6 degrees: 6/12
- 33.7 degrees: 8/12
- 39.8 degrees: 10/12
Safety
Measuring from the attic or a gable end on a ladder is safer than walking the roof. For professional takeoffs, see how roofers measure a roof.