Hip Roof Calculator

A hip roof slopes down to the eaves on all four sides. Enter the length and width of the building at the walls, the pitch and the overhang to get the roof area, the ridge and hip lengths, the common and hip rafter lengths, and a shingle count.

This is for a regular hip roof on a rectangle: all four planes have the same pitch and the eaves are level all the way around. Dutch hips (a small gable at the top), hips with steeper ends, and L- or T-shaped hip roofs with valleys need to be split into sections. See how to measure a hip roof below.

Hip roof formulas

Why area is just outline × multiplier. Every plane of a regular hip roof tilts at the same angle, so the whole roof is the flat outline stretched by one factor. The triangles and trapezoids don't need separate math, and a hip roof has exactly the same area as a gable roof on the same rectangle at the same pitch. The roof area calculator uses the same formula.

Why the ridge is length minus width. Each end plane rises at the same pitch as the long sides, so it has the same horizontal run: half the width. The ridge therefore stops half the width in from each end, which leaves length − width. The overhang adds the same amount to both, so it cancels out.

Why hips use a different factor. A hip runs diagonally across the corner. For every 12 inches of common-rafter run it covers about 16.97 inches of level run (12 × √2) while rising the same height, so it is longer than a common rafter. That is the hip/valley factor: 1.5 at 6/12, 1.7321 at 12/12.

Worked example

Hip/valley factor by pitch

Multiply the run (half the outline width) by the factor. Lengths are to the ridge centerline, before any ridge-board deduction. The pitch to degrees chart lists the factors for every pitch from 1/12 to 24/12.

How to measure a hip roof

You can get everything this calculator needs without climbing on the roof.

1. Length and width. Tape the long wall and an end wall at the siding or foundation. House plans or the county assessor's sketch work too; check one wall to be sure.
2. Overhang. Measure level from the wall to the face of the fascia, under a long side and under an end. Hip roofs usually have the same overhang all around. If they differ, measure the outline fascia to fascia instead, enter it as the length and width, and set the overhang to 0. Area, ridge and hips come out the same.
3. Pitch. In the attic, hold a level against the underside of a common rafter, mark 12 inches along the level and measure up to the rafter: that is the rise per 12. From a ladder at the eave, a level and tape on the shingles do the same job. Finding your roof pitch covers both methods.
4. Check that it's a regular hip. From the ground, the ridge should end about half the building width in from each end wall (14 ft in on a 28 ft wide house), and from above each hip should split its corner at 45°. In the attic, the rafters on the end walls should have the same rise per 12 as the side rafters. If the ridge is clearly longer or shorter than length − width, the ends are pitched differently: measure each plane with the multi-section roof calculator.
5. Add wings separately. A garage or porch with its own hip roof is its own rectangle. Where two hip roofs meet you get valleys, which add cutting waste and ice-barrier footage.

Stay off steep, wet or two-story roofs unless you have fall protection. Every measurement above can be taken from the ground, a ladder at the eave, or the attic.

Hip roof vs gable roof: what changes in the order

Same house as the example, 40 × 28 ft at 6/12 with 12 in overhangs, built both ways:

• Waste goes up. Every course is cut at a hip on both ends, and the offcuts are rarely long enough to reuse. RoofGenius uses 15% for hip roofs and 10% for simple gables; the waste factor calculator adjusts for extra hips and valleys.
• More cap, less ridge. Hips are covered with the same hip and ridge cap as the ridge, so cap footage usually rises even though the ridge gets shorter. The drip edge and ridge cap calculator takes the exact coverage from the wrapper.
• No rakes. There is no rake trim, and starter goes on the eaves only, but the eaves (and gutters) run around all four sides.
• Short ridge, less ridge vent. A short ridge leaves little room for ridge vent, so hip roofs often add other exhaust vents to balance the soffit intake. Size it from the vent maker's net free area figures.

For framers

• Plumb cuts: commons use the rise on 12 of a framing square; hips use the rise on 17, because a hip covers about 17 in of level run for each 12 in of common run.
• Jack rafters get shorter by the same amount each step: on-center spacing × pitch multiplier. At 16 in on center and 6/12 that is 17-7/8".
• Deductions: the lengths here run to the ridge centerline. Shorten commons by half the ridge thickness (measured level), and shorten hips for where they meet the ridge and the commons. Hips also need 45° side cuts at the top.
• Rafter and hip sizes come from your code's span tables or an engineer. For a single rafter with cut angles and a ridge-board deduction, use the rafter length calculator.

Last reviewed 2026-10-20. Results are estimates for planning; confirm quantities with your supplier and requirements with your local building code and the manufacturer's instructions.