Roof Pitch CalculatorEstimate Pitch, Angle, and Slope
Use this free roof pitch calculator to instantly convert between roof pitch, roof angle in degrees, and slope percentage. Choose Find Pitch mode to calculate pitch from rise and run, or Find Rise mode to calculate the rise from a known pitch and run.
Getting started
How to use this roof pitch calculator
1
Select calculation mode
Find Pitch (if you have rise and run measurements) or Find Rise (if you know the pitch ratio and run).
2
Enter your measurements
For Find Pitch, enter rise and run in the same unit. For Find Rise, enter the pitch numerator and horizontal run.
3
Read results
Read the pitch ratio, angle in degrees, and slope percentage from the result card.
4
Review the details
Review the step-by-step breakdown and reference table below.
The calculation
Step-by-step: how your roof pitch was calculated
1
Compute pitch ratio (rise per 12 units of run)
Pitch = (Rise / Run) x 12 = (6 / 12) x 12
2
Calculate roof angle in degrees
Angle = arctan(Rise / Run) = arctan(6 / 12)
3
Calculate slope percentage
Slope % = (Rise / Run) x 100 = (6 / 12) x 100
Formulas
Roof pitch formulas
Find pitch from rise and run:
Pitch = (Rise / Run) x 12
Find rise from pitch and run:
Rise = Run x (Pitch / 12)
Derived values (both modes):
Angle (deg) = arctan(Rise / Run) x (180 / PI)
Slope (%) = (Rise / Run) x 100
Note: in the imperial pitch system, the denominator is always 12. A pitch of 6/12 means the roof rises 6 units for every 12 units of horizontal run.
Reference Table
Roof pitch reference table
The table below shows common residential pitches in all three formats: imperial ratio (X/12), angle in degrees, and slope percentage, with a typical application note for each.
Background Information
Understanding roof pitch
Roof pitch is more than an aesthetic choice - it drives drainage performance, snow and wind load behavior, material compatibility, and the amount of attic space available. Getting the pitch right at the design stage and verifying it accurately in the field are both critical.
Most residential roofs in North America fall into the 4/12 to 8/12 pitch range. Within this range, standard three-tab or architectural asphalt shingles perform reliably. Steeper pitches shed water faster but require more material.
Context
What the results mean
Pitch ratio (X/12)
The pitch ratio is the standard notation used in North American construction documents and building code references. A pitch of 6/12 means 6 inches of rise for every 12 inches of run.
Angle in degrees
The angle in degrees is what you set on a sliding bevel, digital angle finder, or circular saw to make plumb cuts for the rafter installation. A 6/12 pitch corresponds to 26.57 degrees.
Slope percentage
Slope percentage is the standard format in European construction and civil engineering. A 50% slope (6/12 in imperial) means the roof rises 50 cm for every 100 cm of run.
Mistakes
Common mistakes when calculating roof pitch
Confusing rise with run
Rise is the vertical measurement; run is the horizontal measurement. Swapping them inverts the pitch and produces nonsense angles. Always measure rise vertically and run horizontally.
Measuring along the slope instead of horizontally
The run in the pitch formula must be measured horizontally, not along the slope of the rafter. Measuring along the rafter surface gives the hypotenuse, not the run leg.
Using inconsistent units in Find Pitch mode
In Find Pitch mode, rise and run must be in the same unit. Entering rise in inches (e.g., 6 inches) and run in feet (e.g., 12 feet) produces an incorrect pitch. Convert to the same unit first.
FAQ
Frequently asked questions
Q
What is roof pitch and what do the numbers mean?
Roof pitch is expressed as X/12 in imperial measure - meaning the roof rises X inches for every 12 inches of horizontal run. A 6/12 pitch means the roof rises 6 inches for each foot of run. A 4/12 pitch is a common low-slope residential roof; a 12/12 pitch is a steep 45-degree roof.
Q
How do I measure roof pitch from inside the attic?
Place a level on the rafter. Mark 12 inches in from one end along the level. At that mark, measure straight down to the rafter. The distance in inches is the pitch numerator. For example, if you measure 6 inches down at 12 inches along, the pitch is 6/12.
Q
What is the difference between roof pitch, slope, and angle?
All three describe the steepness of a roof in different formats. Pitch (e.g., 6/12) is used in US and Canadian construction. Slope percentage (50%) is used in European and civil engineering contexts - it is the rise expressed as a percentage of the run. Roof angle in degrees is used with tools like clinometers and for specialized structural calculations.
Q
Can I use this roof pitch calculator for metric roofs?
Yes. In metric mode, enter the rise and run in the same unit (centimeters or meters). The calculated pitch percentage (slope %) and angle in degrees are the same dimensionally regardless of unit system. The numeric pitch ratio will differ from imperial notation.
Q
What pitch is best for asphalt shingles?
Asphalt shingles work best from 4/12 to 12/12 pitch. Below 4/12, wind-driven rain can get under standard shingles. Between 2/12 and 4/12 (low slope), modified asphalt or ice-and-water shield starter courses are required throughout. Below 2/12 requires a fully adhered roofing membrane.
Q
How does roof pitch affect material quantity?
Steeper roofs have more actual surface area than their footprint suggests. A 12/12 pitch has 41% more surface area than a flat roof of the same plan area. Multiply your horizontal roof area by the roof pitch factor (1 / cos(angle)) to get the actual sloped surface area for accurate shingle ordering.
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