Roof area calculator Hip

A hip roof slopes down on all four sides: two trapezoid slopes on the long sides and two triangular hips at the ends. It has no gable walls, is very stable in strong wind and gives an even overhang all around the house.

What you need to measure

• L: the length of the building along the eaves.
• l: the width of the building.
• C: the length of the ridge. On a square building the ridge is 0 and the roof becomes a pyramid.
• H: the rise, the height of the ridge above the eaves.

How the area is calculated

The long sides are trapezoids with L at the eave, C at the ridge and the rafter √((l / 2)² + H²) as height.

Each hip end is a triangle with base l. The ridge stops (L − C) / 2 from each end, so the triangle height is √(((L − C) / 2)² + H²).

Roof area = 2 × trapezoid + 2 × triangle.

Worked example

1. L = 12 m, l = 8 m, C = 4 m, H = 3 m.
2. Long sides: rafter = √(4² + 3²) = 5 m, each trapezoid = (12 + 4) / 2 × 5 = 40 m².
3. Hip ends: (12 − 4) / 2 = 4 m, slope = √(4² + 3²) = 5 m, each triangle = 8 × 5 / 2 = 20 m².
4. Roof area = 2 × 40 + 2 × 20 = 120 m². The 12 × 8 m floor is 96 m², and 96 × 5 / 4 = 120 m² confirms it.

Tips before you order materials

• A quick check for any roof with equal slopes: floor area (with overhangs) × rafter / run.
• Four hips mean four hip caps and more cutting: plan 15% extra material.
• Gutters run all around a hip roof: the gutter length is the full perimeter.

Frequently asked questions

What if the hip ends are steeper than the long sides?

Enter the real ridge length C. The calculator works out the pitch of the hips and of the long sides separately and shows both.

How do I find the ridge length from the ground?

For equal pitches, the ridge is L − l. On a 12 × 8 m house with equal slopes the ridge is 4 m.