Roof measurement
Gable roof area calculator
Estimate gable roof area. Simple two-slope gable roof.
Try the calculation
Use one equal gable section with two slopes.
Adjustable example. Change these illustrative inputs to match your task, then recalculate. Reset restores the example and its result.
Understand the result
How this calculation works
An equal-gable estimate doubles one sloped triangular section across the roof length.
Steps
- Enter roof length, half-span/run and rise for the same section.
- Use feet for all three measurements.
The form starts with the worked example below. Change its values and selections to match your task; Reset restores the example.
Formula
area = 2 × length × √(run² + rise²).
Variables and units
- Roof length (ft)
- Required. Use a positive value. Starting example: 40. Replace it for your task.
- Half-span/run (ft)
- Required. Use a positive value. Starting example: 15. Replace it for your task.
- Rise (ft)
- Required. Use a positive value. Starting example: 6. Replace it for your task.
What the result means
It assumes two matching slopes. Gables, overhangs and irregular additions need separate measurements.
Worked example
Inputs: Roof length = 40; Half-span/run = 15; Rise = 6.
Calculation: 2 × 40 × √(15² + 6²) = 1,292.44 sq ft.
Result: 1,292.44 sq ft.
Frequently asked questions
Why is run a half-span?
Each side of a symmetric gable uses half the horizontal width.
Does it include overhang?
No, include the overhang in the measured dimensions if appropriate.
Can the two sides differ?
Use measured-plane totals instead of this equal-gable model.