Knowing the roof pitch helps with roof measurements, material estimates, drainage considerations and calculating the actual sloping length of a roof.
Roof pitch can be expressed as a ratio, percentage or angle. These describe the same roof geometry in different ways, but they should not be confused with one another.
What Is Roof Pitch?
Roof pitch describes how much a roof rises vertically over a given horizontal distance.
For example, a 6:12 roof pitch rises 6 units for every 12 units of horizontal run. The same ratio can be simplified mathematically, but roofing measurements commonly retain the 12-inch run format in North American construction.
When the rise and run use the same units, the ratio can be calculated directly.
How to Calculate Roof Pitch From Rise and Run
Suppose a roof rises 4 metres over a horizontal run of 8 metres.
To express this as a ratio using a 12-unit run:
So the roof pitch is 6:12.
Rise: 4 m
Run: 8 m
Rise divided by run: 0.5
Equivalent 12-unit rise: 6
Roof pitch: 6:12
How to Calculate Roof Pitch From Measurements
If you can safely obtain the roof's rise and horizontal run, the calculation is straightforward.
- Measure the horizontal run.
- Measure the vertical rise over that run.
- Make sure both measurements use the same unit.
- Divide rise by run.
- Convert the result into the pitch format you need.
How Roof Pitch Is Written
Roof pitch is commonly written as a ratio such as:
- 3:12
- 4:12
- 5:12
- 6:12
- 8:12
- 10:12
- 12:12
The first number represents the rise, while the second number represents the horizontal run.
For example, 8:12 means the roof rises 8 units for every 12 units of horizontal run.
Roof Pitch to Angle
Roof pitch can also be expressed as an angle. To convert a pitch ratio to an angle, use the inverse tangent of rise divided by run.
For a 6:12 roof:
The resulting angle is approximately 26.57 degrees.
| Roof pitch | Rise per 12 units | Approx. angle |
|---|---|---|
| 2:12 | 2 | 9.46 degrees |
| 3:12 | 3 | 14.04 degrees |
| 4:12 | 4 | 18.43 degrees |
| 5:12 | 5 | 22.62 degrees |
| 6:12 | 6 | 26.57 degrees |
| 8:12 | 8 | 33.69 degrees |
| 10:12 | 10 | 39.81 degrees |
| 12:12 | 12 | 45 degrees |
These angle values are mathematical conversions. Roofing material requirements and installation limits should be checked against the manufacturer's specifications.
Roof Pitch as a Percentage
Roof slope can also be expressed as a percentage.
For a 6:12 roof:
Therefore, a 6:12 pitch corresponds mathematically to a 50 percent slope.
How to Calculate Roof Pitch From a Roof's Vertical Rise
If you know the roof rise and the horizontal run, you can calculate the pitch directly.
Rise: 3 ft
Run: 12 ft
Pitch: 3:12
Slope percentage: 25 percent
Approximate angle: 14.04 degrees
The same calculation works with metres, centimetres, millimetres or other units as long as the rise and run use the same unit.
How Roof Pitch Affects Roof Area
A roof with a steeper pitch has a longer sloping surface than a roof with a lower pitch covering the same horizontal footprint.
This matters when calculating roofing materials because the actual surface to be covered follows the slope of the roof.
For example, if one side of a gable roof has a horizontal run of 3 metres and a rise of 2 metres, the sloping length is:
The result is approximately 3.606 metres.
If the roof plane is 10 metres long:
For two equal roof planes, the total surface area would be approximately 72.12 square metres before accounting for overhangs or other roof features.
For a detailed explanation of this calculation, see How to Calculate Roof Area.
Pitch, Rise and Run: What Is the Difference?
| Term | Meaning |
|---|---|
| Rise | The vertical distance the roof increases in height. |
| Run | The horizontal distance associated with the rise. |
| Pitch | The rise-to-run relationship, commonly written as a ratio. |
| Slope percentage | Rise divided by run, multiplied by 100. |
| Roof angle | The angle formed between the roof surface and the horizontal. |
How to Calculate Roof Pitch From Rafter Length
If you know the horizontal run and the actual sloping rafter length, the roof rise can be found using the right triangle formed by the roof.
Once the rise is known, calculate the pitch using rise divided by run.
Suppose the horizontal run is 3 metres and the sloping rafter length is 3.606 metres.
The calculated rise is approximately 2 metres.
The pitch is therefore approximately 2:3, which corresponds to 8:12 when expressed using a 12-unit run.
Why Roof Pitch Matters
Roof pitch affects more than appearance. It can influence the roof surface area, drainage, material requirements and the suitability of certain roofing products.
A roof's pitch may also affect how water and snow move across the roof, although the appropriate design depends on local conditions, building requirements and the roofing system being installed.
Common Roof Pitch Calculation Mistakes
Mixing measurement units
Do not divide a rise measured in metres by a run measured in feet. Convert both measurements to the same unit first.
Confusing pitch with angle
A 6:12 pitch is not a 6-degree roof. The pitch ratio and angle are related mathematically but represent different measurements.
Using the full building width as the run
For a symmetrical gable roof, the run from the eave to the ridge is normally half the building width before accounting for specific overhang geometry.
Ignoring roof overhangs
Overhangs can affect the actual dimensions of the roof plane and should be included when they form part of the roof covering being measured.
Relying on visual estimates
A roof can look relatively shallow or steep without giving you an accurate pitch. Use measured rise and run whenever possible.
Use the Roof Pitch Calculator
Calculate Roof Pitch Quickly
Use the BuildersMeasures Roof Pitch Calculator to calculate roof pitch from rise and run measurements and work with related roof measurements.
Open Roof Pitch CalculatorRoof Pitch and Slope
Roof pitch and slope are closely related, but the terms are often used differently depending on the construction context.
For mathematical calculations, slope is the ratio of vertical change to horizontal change. Roof pitch commonly presents that relationship in a format such as 6:12.
If you need a percentage or angle rather than a pitch ratio, the Slope Calculator can be useful for related measurements.
Frequently Asked Questions
What is the formula for roof pitch?
Roof pitch is calculated by dividing the vertical rise by the horizontal run. The result can then be expressed as a ratio such as 6:12.
What does a 6:12 roof pitch mean?
A 6:12 roof pitch means the roof rises 6 units vertically for every 12 units of horizontal run. It corresponds to a 50 percent slope and an angle of approximately 26.57 degrees.
How do I calculate roof pitch from rise and run?
Divide the rise by the run. If you want the common 12-unit pitch format, multiply that decimal result by 12 to find the corresponding rise over 12 units.
Is roof pitch the same as roof angle?
No. Roof pitch is commonly expressed as a rise-to-run ratio, while roof angle is measured in degrees. They can be converted mathematically.
How do I convert roof pitch to percentage?
Divide the rise by the run and multiply by 100. For example, 6 divided by 12 multiplied by 100 gives a 50 percent slope.
Does roof pitch affect roof area?
Yes. A steeper roof generally has a longer sloping surface over the same horizontal run, increasing the actual roof surface area.
Can I calculate roof pitch without climbing onto the roof?
Yes. Depending on the roof design, rise and run measurements may be obtained from an accessible attic, building plans or measurements taken safely from the ground. Avoid climbing onto a roof solely to measure pitch unless you have appropriate safety equipment and experience.