Roof Pitch Calculator
Instantly determine your roof pitch, angle in degrees, slope multiplier, rafter length, rise, and run. Use this free calculator to convert between measurements for any roofing or framing project.
Enter Roof Dimensions
Enter Pitch & Run
- Angle (Degrees) 0.00°
- Slope Percentage 0.00%
-
Roof Pitch Multiplier
For calculating square footage 1.0000 - Rafter Length (Hypotenuse) 0.00
Understanding your roof pitch is the critical first step before buying shingles, ordering trusses, or calculating the total square footage of your roof. Whether you are dealing with a flat shed or a steep residential gable, measuring the steepness of a roof dictates material choices, structural loading, and water shedding capabilities.
Our professional roof pitch calculator allows you to easily convert between rise and run, fractions (x/12), degrees, and slope multipliers. Below, we break down exactly how these formulas work, how to measure your roof safely, and provide standard conversion charts for common roofing projects.
What is Roof Pitch?
Roof pitch is simply a mathematical representation of a roof’s steepness. In the United States, roof pitch is universally expressed as a fraction over 12, representing the “Rise over Run.”
For example, a 4/12 roof pitch (pronounced “four in twelve”) means that for every 12 inches the roof extends horizontally (the Run), it rises 4 inches vertically (the Rise). While European systems often express roof slope in degrees or percentages, the x/12 format is the standard language of North American carpentry and roofing.
How to Calculate Roof Pitch (Formulas)
Calculating roof slope relies entirely on right-angle trigonometry. If you know the vertical rise and horizontal run, you can find the pitch, angle, and rafter length (the hypotenuse).
Ensure that Rise and Run are measured using the exact same units (e.g., both in inches or both in feet) before dividing.
How to Calculate Roof Pitch in Degrees
To convert a standard x/12 pitch into an angle measured in degrees, you use the inverse tangent (arctangent) function.
Example: What is a 4/12 pitch in degrees?
How to Measure Your Roof Pitch
You can find your roof slope without climbing onto the roof itself. Here are the three most common methods:
Method 1: From the Attic (Safest)
- Go into your attic space and place a standard 12-inch or 24-inch carpenter’s level perfectly horizontally against the bottom edge of a roof rafter.
- Make sure the bubble is centered. If using a 24-inch level, mark the 12-inch point on the top edge of the level.
- Use a tape measure to measure the straight vertical distance from the 12-inch mark on your level directly up to the bottom edge of the rafter.
- If that vertical measurement is 5 inches, your roof pitch is exactly 5/12.
Method 2: Using a Smartphone App
Modern smartphones have built-in gyroscopes. You can use apps like the Apple “Measure” app (Level tool) or various Android bubble level apps. Simply lay your phone flat against the angled roof surface or underside of a rafter to get an instant reading in degrees, then use our calculator above to convert degrees to a standard pitch.
The Roof Pitch Multiplier Explained
If you are trying to calculate the total square footage of roofing materials (shingles, underlayment) needed, you cannot simply measure the flat footprint of your house. A sloped roof has significantly more surface area than a flat ceiling below it.
To find the true roof area, you take the flat square footage (footprint + overhangs) and multiply it by the Roof Pitch Multiplier. This multiplier is the secant of the roof angle.
Example: A house has a flat footprint of 1,000 sq ft and a 6/12 pitch. The multiplier for 6/12 is 1.118. Therefore, the actual roof surface area is 1,000 × 1.118 = 1,118 square feet.
Roof Pitch to Degrees Conversion Chart
Use this quick reference chart to convert common pitch formats, find their equivalent angles, and determine the exact slope multiplier for material calculations.
| Roof Pitch (x/12) | Angle (Degrees) | Roof Multiplier | Common Application |
|---|---|---|---|
| 1/12 | 4.76° | 1.0035 | Flat / Rubber Roofs |
| 2/12 | 9.46° | 1.0138 | Shed / Lean-to |
| 3/12 | 14.04° | 1.0308 | Low Slope (Metal/Roll) |
| 4/12 | 18.43° | 1.0541 | Standard Residential (Min for Shingles) |
| 5/12 | 22.62° | 1.0833 | Standard Residential |
| 6/12 | 26.57° | 1.1180 | Standard Residential |
| 7/12 | 30.26° | 1.1577 | Medium Steep |
| 8/12 | 33.69° | 1.2019 | Medium Steep |
| 9/12 | 36.87° | 1.2500 | Steep |
| 10/12 | 39.81° | 1.3017 | Steep |
| 12/12 | 45.00° | 1.4142 | A-Frame / Very Steep |
Common Slope Calculation Mistakes
- Mixing up Rise and Run: Rise is always the vertical measurement (up and down). Run is always horizontal. Swapping them will result in a completely incorrect angle.
- Using Asphalt Shingles on Low Pitches: Standard architectural asphalt shingles typically require a minimum pitch of 4/12. Installing them on a 2/12 or 3/12 roof will often lead to water backing up under the shingles, requiring specialized underlayment or roll roofing instead.
- Measuring the Top of Existing Shingles: If you are measuring pitch from the outside, the uneven texture of existing shingles can throw off your level. It is much more accurate to measure the bare wood rafter in the attic or the fascia board.
Frequently Asked Questions
A 4/12 roof pitch means the roof rises 4 inches vertically for every 12 inches it extends horizontally. The formula to find the angle is Angle = arctan(Rise ÷ Run). For a 4/12 pitch, you calculate arctan(4 ÷ 12), which results in an angle of 18.43 degrees.
A roof angle of exactly 22.5 degrees corresponds to a 5/12 roof pitch. Technically, a 5/12 pitch is 22.62 degrees, which is the closest standard framing pitch to 22.5 degrees. To convert degrees to pitch manually, calculate tan(Angle) × 12.
A 3/12 roof pitch calculator is a tool used to determine the exact rafter length, total rise, and slope multiplier for a roof that rises 3 inches per 12 inches of run. It helps estimate roofing materials for low-slope applications.
To calculate your pitch, place a level horizontally against the roof rafters (or on the roof surface). Measure 12 inches exactly along the bottom of the level to find the ‘run’. Then, measure the vertical distance straight down from that 12-inch mark to the roof. That vertical measurement is your ‘rise’.
You can calculate your roof pitch from the ground or attic. In the attic, measure 12 inches horizontally along a level placed against the bottom of a rafter. Then measure vertically from the 12-inch mark straight up to the rafter. If it’s 6 inches, your pitch is 6/12.
Yes, both iOS and Android smartphones have built-in leveling tools (like the Apple Measure app). By placing the edge of your smartphone directly against the sloping rafter or roof surface, the app will read the exact angle in degrees, which you can then convert to a standard pitch.
While online tools cannot physically measure your roof via a camera accurately, you can use a free online roof pitch calculator (like the one on this page) to instantly convert your basic measurements into pitch, degrees, slope multiplier, and exact rafter length.
Reference: https://en.wikipedia.org/wiki/Roof_pitch