Enter the roof span (eave-to-eave horizontal distance), the roof pitch angle, and the horizontal overhang length (one side) into the calculator to determine the roof panel length (slope length from ridge to the end of the overhang).

Roof Panel Length Calculator

Panel Length
Panel Count & Material

Enter the roof span (eave-to-eave), pitch angle, and horizontal overhang (one side) to calculate the roof panel length (slope length from ridge to fascia).

Related Calculators

Roof Panel Length Formula

The following formula is used to calculate the roof panel length for one side of a symmetrical gable roof, where the span is measured horizontally from eave to eave and the overhang is a horizontal projection on that side. Variables: 

L = ((S/2) + O) / cos(a)
  • L is the roof panel length along the slope (ridge to the end of the overhang)
  • S is the roof span (horizontal distance from eave to eave)
  • a is the roof pitch angle measured from horizontal
  • O is the horizontal overhang length on one side

To calculate the roof panel length, take half the roof span to get the horizontal run for one side, add the horizontal overhang, and then divide by the cosine of the roof pitch angle.

What is a Roof Panel Length?

A roof panel length is the end-to-end measurement of a roofing panel along the roof slope. This length depends on the building geometry and whether the panel runs from ridge to eave (often as a single piece) or must be lapped/spliced due to product, handling, or transport limits. Accurate panel length helps ensure proper fit and can reduce waste.

How to Calculate Roof Panel Length?

The following steps outline how to calculate the Roof Panel Length.

  1. First, determine the span of the roof (S) as the horizontal distance from eave to eave.
  2. Next, determine the roof pitch angle (a), measured from horizontal.
  3. Next, determine the horizontal overhang length on one side (O).
  4. Next, calculate the cosine of the roof pitch angle (cos(a)).
  5. Finally, calculate the Roof Panel Length (L) using the formula: L = ((S/2) + O) / cos(a).

Example Problem:

Use the following variables as an example problem to test your knowledge.

Span of the roof (S) = 10 ft

Roof pitch angle (a) = 30 degrees

Overhang length (O) = 2 ft