Measure Roof Pitch with a Speed Square
The professional framer's method — read your roof angle directly in seconds. Works from the attic or roof surface.
What Is a Speed Square?
A speed square (also called a rafter square) is a triangular tool used by carpenters and framers. It has degree markings and pitch markings (1/12 through 12/12) engraved on it, making it perfect for measuring roof angles. Swanson, Empire, and Stanley all make popular versions — typically $10-20.
Step-by-Step Method
- 1. Access a rafter. Easiest from inside the attic. You can also do this on the roof surface.
- 2. Position the pivot point. The pivot is the corner with the small hole. Place it against the bottom edge of the rafter.
- 3. Rotate the square. Keep the pivot pressed firmly against the rafter. Rotate the square so that its horizontal edge is perfectly level (use a torpedo level on top to check).
- 4. Read the angle. Where the rafter bottom edge crosses the degree scale, that number is your pitch angle in degrees.
- 5. OR read the pitch directly. Most speed squares have pitch markings (2/12, 4/12, 6/12, etc.) as well — read those directly where the rafter crosses.
Common Pitch → Angle Reference
| Pitch | Angle | Common Use |
|---|---|---|
| 3:12 | 14° | Low-slope, modern |
| 4:12 | 18.4° | Minimum for shingles |
| 6:12 | 26.6° | Most common residential |
| 8:12 | 33.7° | Classic colonial |
| 10:12 | 39.8° | Steep/Victorian |
| 12:12 | 45° | 45-degree iconic |
💡 Pro Tips
- • Always verify with a torpedo level on top — even a tiny tilt throws off the reading
- • Measure at least 2 different rafters to confirm consistency
- • Use a 7" speed square for precision; 12" framing squares work too but are less handy
- • Some speed squares have a built-in angle finder with a level bubble — these are fastest and most accurate