Roof measurement
Lean-to roof area calculator
Estimate lean-to/shed roof area. Garage, shed, porch, or addition.
Try the calculation
Use one single-slope roof plane.
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
A lean-to area estimate uses one sloped plane across the full roof length.
Steps
- Enter roof length, horizontal run and vertical rise for the plane.
The form starts with the worked example below. Change its values and selections to match your task; Reset restores the example.
Formula
area = length × √(run² + rise²).
Variables and units
- Roof length (ft)
- Required. Use a positive value. Starting example: 30. Replace it for your task.
- Run (ft)
- Required. Use a positive value. Starting example: 12. Replace it for your task.
- Rise (ft)
- Required. Use a positive value. Starting example: 4. Replace it for your task.
What the result means
It represents one plane and does not decide how the plane meets walls or edges.
Worked example
Inputs: Roof length = 30; Run = 12; Rise = 4.
Calculation: 30 × √(12² + 4²) = 379.47 sq ft.
Result: 379.47 sq ft.
Frequently asked questions
Does run equal the roof depth?
Yes, enter the horizontal projection.
Can the roof have a different pitch at one end?
No, split the measured surfaces.
Is this the footprint area?
No, it is the sloped surface estimate.