Roof Pitch Calculator: Rise, Run, and Slope Angle
Convert between X:12 ratio, degrees, and percent. All three update on every keystroke.
X:12 Ratio
7.00:12
Angle
30.26 °
Percent
58.3 %
Common Pitch Reference
| Ratio (X:12) | Degrees | Percent | Notes |
|---|---|---|---|
| 2:12 | 9.5° | 17% | Low slope |
| 3:12 | 14.0° | 25% | Low slope |
| 4:12 | 18.4° | 33% | Low slope |
| 6:12 | 26.6° | 50% | Conventional gable |
| 8:12 | 33.7° | 67% | Conventional gable |
| 9:12 | 36.9° | 75% | Conventional gable |
| 10:12 | 39.8° | 83% | Gambrel lower |
| 12:12 | 45.0° | 100% | Steep / 45° |
| 16:12 | 53.1° | 133% | Gambrel lower |
| 20:12 | 59.0° | 167% | Gambrel lower |
| 24:12 | 63.4° | 200% | Gambrel lower |
Reading a Pitch Gauge
A pitch gauge is a small protractor with a level bubble. Hold it flat against the rafter or against a board pulled diagonally between rafter top and ceiling joist. The bubble reads degrees directly. Convert to X:12 in your head with two anchor points: 27° ≈ 6:12, and 45° = 12:12.
Gambrel Pitch Combinations
Gambrel lower pitches of 60–75° pair with upper pitches of 15–30°. The traditional 60°/15° pair (half-circle method) gives the classic barn silhouette. A 67.5°/22.5° pair makes the upper roof slightly steeper for better shedding, common in snow country. A 75°/30° pair maximizes second-floor headroom but is the hardest to sheath because the lower slope approaches vertical.
Where to Start
If you are not locked into a specific look yet, start at 60° lower and 15° upper. It matches the traditional half-circle barn standard, needs no separate math to balance the two rafters, and sits comfortably within the framing capacity of standard 2×8 lumber. Move to a steeper 67.5°/22.5° pair only once you know you want the extra headroom badly enough to pay for larger lumber.
Frequently Asked Questions
›What is roof pitch?
Roof pitch is the steepness of a rafter, expressed three ways: as a rise/run ratio (commonly X:12), as an angle in degrees, or as a percentage slope. A 12:12 pitch rises 12 inches over 12 inches of horizontal run, which equals 45° or 100%.
›What pitch is a gambrel lower rafter?
Gambrel lower rafters typically run 60° to 75° from horizontal: that is 21:12 to 45:12 in rise/run, or 173% to 373% slope. The half-circle barn standard is 60° (21:12).
›What pitch is a gambrel upper rafter?
Gambrel upper rafters run 15° to 30° from horizontal: 3:12 to 7:12 in rise/run. In the half-circle method the upper pitch is always exactly 45° less than the lower pitch.
›How do I convert pitch in degrees to X:12?
Multiply tan(degrees) by 12. Example: tan(30°) × 12 = 6.93, so 30° ≈ 7:12. The calculator above does all three conversions in real time.
›What does pitch in percent mean?
Percent slope is rise divided by run × 100. A 12:12 pitch is 100%; a 6:12 is 50%; a 60° gambrel lower rafter is about 173%.