Quick answer: Roof pitch is the number of inches a roof rises for every 12 inches of horizontal run. A roof that rises 6 inches per 12 inches has a 6/12 pitch, which is 26.6° or a 50% slope.
Roof pitch decides which roofing materials you can use, how much a roof replacement costs and how much surface area the roof has. Here is how to measure it safely and convert it to the format you need.
Pitch, Slope and Angle
- Pitch (US and Canada): rise per 12 of run, written as 6/12 or 6:12.
- Angle (UK, Europe, Australia): degrees from horizontal, such as 30°.
- Slope percent: rise ÷ run × 100, so 6/12 is 50%.
Method 1: From the Attic
This is the safest way. Hold a level horizontally against the bottom edge of a rafter. Mark the level 12 inches from the point where it touches the rafter, then measure straight up from that mark to the underside of the rafter. That vertical distance is the rise per 12.
Method 2: On the Roof with a Level
Only if it is safe to do so: place a 12 inch (or 2 ft) level on the roof surface with one end touching the shingles, hold it level, and measure from the other end straight down to the roof. If you used a 24 inch level, divide the measurement by two.
Method 3: From the Gable End
On a simple gable house, measure the height from the top of the wall to the ridge (the rise) and half the width of the house (the run). Divide rise by run and multiply by 12. A rise of 7.5 ft over a run of 15 ft gives 0.5 × 12 = 6/12.
Method 4: Phone App or Pitch Gauge
Many smartphone level apps show an angle in degrees. Place the phone on a rafter or on a straight board against the roof and read the angle, then convert it with the chart below.
Skip the math: enter rise and run and get the pitch, degrees, slope percent, multiplier and rafter length. Open the free Roof Pitch Calculator →
Roof Pitch to Degrees Chart
| Pitch | Angle | Slope | Multiplier |
|---|---|---|---|
| 2/12 | 9.5° | 16.7% | 1.014 |
| 3/12 | 14° | 25% | 1.031 |
| 4/12 | 18.4° | 33.3% | 1.054 |
| 5/12 | 22.6° | 41.7% | 1.083 |
| 6/12 | 26.6° | 50% | 1.118 |
| 7/12 | 30.3° | 58.3% | 1.158 |
| 8/12 | 33.7° | 66.7% | 1.202 |
| 9/12 | 36.9° | 75% | 1.25 |
| 10/12 | 39.8° | 83.3% | 1.302 |
| 12/12 | 45° | 100% | 1.414 |
Converting Between Formats
Degrees = arctan(Rise ÷ Run)
Pitch (x/12) = tan(Degrees) × 12
For example, a 35° roof in the UK is tan(35°) × 12 = 8.4/12.
What Pitch Means for Your Roof
- Below 2/12: treated as low-slope; needs membrane roofing rather than shingles.
- 2/12 to 4/12: shingles possible with extra underlayment; check the manufacturer’s minimum.
- 4/12 to 9/12: conventional pitch; easiest to work on.
- Above 9/12: steep; more expensive to install due to safety equipment.
Next step: use the multiplier to work out how many squares your roof is.
Frequently Asked Questions
What is the most common roof pitch?
Between 4/12 and 9/12 for houses in North America, with 6/12 being very common.
Is a 4/12 roof pitch good?
Yes. It is a conventional pitch that sheds water well, is suitable for asphalt shingles and is relatively easy to walk on.
How do I convert 30 degrees to roof pitch?
tan(30°) × 12 = 6.9, so a 30° roof is approximately a 7/12 pitch.
Related Guides
- How Many Squares Is My Roof? How to Measure a Roof from the Ground
- How Many Fence Posts Do I Need? (With Corners and Gates)
- How Many Deck Boards Do I Need? (12×12, 12×16 and 16×20 Decks)
Try the free Roof Pitch Calculator or browse all home improvement calculators.