4/12 Roof Pitch
Convert a 4/12 roof pitch to degrees and slope percentage, understand its geometry, and calculate rafter length and pitch factor using your own measurements.
A 4/12 roof pitch rises 4 inches for every 12 inches of horizontal run. It equals approximately 18.43°, has a 33.33% roof slope, and a 1.054 pitch factor.
What Does a 4/12 Roof Pitch Mean?
A 4/12 roof pitch means the roof rises 4 units vertically for every 12 units it travels horizontally. When measured in inches, that is a 4-inch rise for every 12 inches of run.
The same roof incline can also be expressed as a 4/12 roof pitch angle of 18.43 degrees or as a 33.33% slope.
Compared with steeper pitches such as 6/12 or 8/12, a 4/12 pitch has a lower incline while still forming a clearly sloped roof surface.
Calculate a 4/12 Roof Pitch
The calculator below is preloaded with a 4-inch rise and 12-inch run. Change either measurement to calculate a different roof pitch instantly.
Enter your roof measurements and calculate instantly.
How a 4/12 Roof Pitch Is Calculated
A 4/12 pitch can be converted into angle, slope percentage and sloped length using basic roof geometry.
4/12 Roof Pitch Angle
Divide rise by run and calculate the arctangent.
Therefore, a 4/12 roof pitch in degrees is approximately 18.43°.
4/12 Roof Slope
Roof slope percentage compares rise with horizontal run.
A 4/12 roof therefore has a 33.33% slope.
Sloped Length
For a 12-inch horizontal run, use the Pythagorean relationship.
The sloped length is approximately 12.65 inches.
4/12 Rafter Length and Pitch Factor
These values help convert horizontal run into approximate sloped roof length for a simple right-triangle roof section.
Rafter Length per 12-Inch Run
12.65 inWith a 4-inch rise and 12-inch horizontal run, the calculated diagonal length is approximately 12.65 inches before accounting for overhangs, ridge details or other construction adjustments.
4/12 Pitch Factor
1.054The 4/12 pitch factor is approximately 1.054. Multiplying horizontal run by this factor gives an approximate corresponding sloped length for the same simple geometry.
4/12 Roof Pitch Conversion Table
Quick reference values for a standard 4-over-12 roof incline.
| Measurement | 4/12 Value |
|---|---|
| Pitch Ratio | 4:12 |
| Angle in Degrees | 18.43° |
| Slope Percentage | 33.33% |
| Rise per 12 in Run | 4 in |
| Rafter Length per 12 in Run | 12.65 in |
| Pitch Factor | 1.054 |
4/12 vs 6/12 Roof Pitch
Comparing common roof pitches makes the difference in roof steepness easier to understand.
4/12 Roof Pitch
18.43°A 4/12 pitch has a 33.33% slope and a pitch factor of approximately 1.054.
Rise: 4 in per 12 in run6/12 Roof Pitch
26.57°A 6/12 pitch is steeper, with a 50% slope and a pitch factor of approximately 1.118.
View 6/12 roof pitch details →4/12 Roof Pitch FAQs
Answers to common questions about 4/12 roof pitch, angle, slope and measurements.
What is a 4/12 roof pitch in degrees?
A 4/12 roof pitch is approximately 18.43 degrees.
What percentage slope is a 4/12 roof?
A 4/12 roof has a slope of approximately 33.33%, calculated by dividing 4 by 12 and multiplying by 100.
What does 4/12 roof pitch mean?
It means the roof rises 4 units vertically for every 12 units of horizontal run. The units can be inches, feet, centimeters or another consistent measurement unit.
What is the pitch factor for a 4/12 roof?
The 4/12 pitch factor is approximately 1.054. It represents the ratio between the sloped length and horizontal run for this simple roof geometry.
What is the rafter length for a 4/12 pitch?
For exactly 12 inches of horizontal run and 4 inches of rise, the simple diagonal length is approximately 12.65 inches. Actual rafters can require additional dimensions for overhangs, ridge connections and other details.
Is a 4/12 roof flatter than a 6/12 roof?
Yes. A 4/12 roof has an angle of about 18.43°, while a 6/12 roof has an angle of about 26.57°. The 6/12 roof therefore has the steeper incline.
Can I use the calculator with measurements other than inches?
Yes. Rise and run can use another consistent unit. The pitch ratio and angle depend on their relationship, while the calculated length follows the selected unit.
Calculate Another Roof Pitch
Use the full Roof Pitch Calculator to convert any rise and run measurement into pitch ratio, angle, slope, rafter length and pitch factor.
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