Roof Pitch Slope Calculator

Calculator Inputs

Calculation Mode

Length Unit

Run

Horizontal distance from wall to ridge centerline.

Rise

Vertical height from run base to ridge point.

Roof Angle (degrees)

Angle between the roof plane and horizontal run.

Pitch Rise per 12

Use 6 for a 6:12 pitch, 8 for 8:12, and so on.

Building Span

Full width of the building. Run becomes span ÷ 2.

Roof Length (optional)

Enter roof length to estimate one-side and both-sides roof area.

Overhang (optional)

Horizontal projection added to the main rafter length.

Example Data Table

These examples show how the calculator converts common roof measurements into pitch, angle, and rafter length values.

Case	Input Method	Rise	Run	Angle	Pitch	Rafter Length
Example 1	Rise and Run	6 ft	12 ft	26.57°	6:12	13.42 ft
Example 2	Rise and Run	8 ft	12 ft	33.69°	8:12	14.42 ft
Example 3	Pitch and Span	10 ft	12 ft	39.81°	10:12	15.62 ft

Formula Used

1. Slope Ratio
Slope = Rise ÷ Run

2. Pitch per 12
Pitch = (Rise ÷ Run) × 12

3. Roof Angle
Angle = arctan(Rise ÷ Run)

4. Grade Percentage
Grade % = (Rise ÷ Run) × 100

5. Rafter Length
Rafter Length = √(Run² + Rise²)

6. Run from Span
Run = Building Span ÷ 2

7. Rise from Pitch and Run
Rise = (Pitch Rise per 12 ÷ 12) × Run

8. Extended Rafter Length
Extended Rafter = Rafter Length + (Overhang × Surface Factor)

Surface factor equals sloped length divided by horizontal run. It converts horizontal overhang into sloped roof length.

How to Use This Calculator

Select the calculation mode that matches your available measurements.
Choose your working unit: feet, meters, or inches.
Enter rise and run, or angle and run, or pitch rise with span.
Add roof length if you want one-side and both-sides area estimates.
Enter overhang if you want a longer rafter estimate.
Press Calculate Roof Pitch to display results above the form.
Review the graph, output cards, and formulas.
Use the CSV or PDF buttons to save your calculation report.

Frequently Asked Questions

1. What is roof pitch?

Roof pitch describes how much a roof rises for every 12 units of horizontal run. A 6:12 pitch means the roof rises 6 units for each 12 units of run.

2. What is the difference between pitch and slope?

Pitch is commonly shown as rise over 12, such as 8:12. Slope is the raw mathematical ratio of rise divided by run, such as 0.6667.

3. Why does the calculator use half the building span?

For a symmetrical gable roof, one rafter covers only one side of the roof. That makes the structural run equal to half of the full building span.

4. What does grade percentage mean here?

Grade percentage converts slope into percent form. A grade of 50% means the roof rises 0.5 units vertically for every 1 horizontal unit.

5. Is rafter length the same as roof area width?

Not exactly. Rafter length is the sloped edge from the wall line to the ridge. It becomes part of the roof area only when multiplied by roof length.

6. How does overhang change the result?

Overhang increases the sloped roof length beyond the wall line. This calculator converts horizontal overhang into extra sloped length using the same roof angle.

7. Can I use meters or inches?

Yes. The calculator supports feet, meters, and inches. Keep all length inputs in the same unit so the result stays consistent and meaningful.

8. Does both-sides roof area fit every roof type?

It fits simple symmetrical two-plane roofs best. Complex roofs with hips, valleys, dormers, or multiple pitch changes need separate section-by-section area calculations.