Roof measurement and quantities
Hip Roof Calculator
Enter measured dimensions to calculate roofing quantities.
Your quantity record
A personal result appears after you enter valid inputs and calculate.
Formula, diagram and sources
Measured surface needs no pitch factor. Footprint surface = length × width × √(1 + (rise / 12)²). For separate planes, sum each projected area × its own factor. Roofing squares = surface / 100.
Equation version 2.0, checked October 14, 2026. Method and source records · Corrections
Last updated October 14, 2026 · Method · Corrections
An equal-pitch hip roof and a gable roof with the same rectangular eave footprint have the same net surface area. Their plane plan areas cover the same footprint, and each uses the same slope factor. Hip cuts and cap lengths still differ. Use separate measured planes for unequal pitches, valleys or additions. Do not multiply the full footprint by the number of roof faces.
Sections11
- Hip roof calculator: equal-pitch rectangular case
- Measure the footprint and common pitch
- Hip roof calculator formula and worked example
- Why hip and gable areas can match
- Separate surface, cuts and accessory quantities
- Unequal pitches and intersecting roofs
- Carry the result into a replacement estimate
- A printable hip-roof measurement record
- Sources and method limits
- Frequently asked questions
- Verdict: geometry first, ordering second
The hip roof calculator estimates the surface of a rectangular roof whose planes all share one pitch. Enter the eave footprint's length and width, then the common rise-in-12. The result is net surface and roofing squares. It does not estimate hip cuts, ridge lengths or a purchase allowance from the roof's name.
Hip roof calculator: equal-pitch rectangular case
A hip roof slopes down toward the eaves on every side. On a simple rectangular form, the ends are triangles and the long sides are trapezoids. A square form can have four triangles meeting at a point. The calculator does not need to guess a ridge length to total the area in this equal-pitch case.
That works because the level plan areas of the roof planes tile the footprint. Each plan area receives the same factor. Adding plan areas first, then multiplying by the common factor, produces the same result as multiplying each plan area and adding the surfaces. This is an area identity, not an assumption that the planes have the same outline.
The footprint must be rectangular at the eaves. A wall plan can omit roof overhangs. An L-shaped house may have valleys that stop its roof from being one rectangular hip. A porch attached to the side can have a different pitch. Check the roof plan before confirming the form's equal-pitch statement.
Measure the footprint and common pitch
Use the length and width of the level eave footprint. Each number should come from a measured plan or measured record. The width runs across the short direction; the length runs across the long direction. Reversing the two does not alter the product. But keep their labels consistent with the drawing.
Pitch means rise per twelve level units. It is not a diagonal hip-rafter angle. The plane's fall from ridge toward its eave gives the pitch needed for surface area. A hip line runs diagonally across the plan and can have a different apparent angle. Copying that angle into the pitch field would use the wrong triangle.
If the report gives pitch in degrees, convert it with the roof pitch calculator. If it gives slope as a percent, keep the unrounded ratio when converting. A rounded chart row is useful for comparison. But the measured ratio remains the firmer input for math.
You do not need to climb onto a roof to use the worksheet. Use existing reports or safe plan records. A photograph can help match the drawing to the building. But it is not a scale measure. OSHA's residential construction guidance describes roof-work fall hazards; the tool gives no access or walking guidance.
Hip roof calculator formula and worked example
Let L and W be eave-footprint dimensions in feet, and let p be rise-in-12. Surface area is A = L × W × √(1 + (p / 12)²). Roofing squares equal A / 100. Keep the unrounded values throughout the calculation and round only the displayed result.
For an assumed 40 by 30 foot footprint at 6:12, plan area is 1200 square feet. The factor is about 1.11803398875. Net surface is about 1341.64 square feet. That is about 13.4164 squares. There is no separate hip surcharge in the area equation.
An independent plane check gives the same total. For this equal-sided roof form, a 10-foot ridge matches the 40-by-30 footprint and equal slopes. Each end's plan triangle has a 30-foot base and 15-foot height, so each plan area is 225 square feet. Each long-side trapezoid has parallel sides of 40 and 10 feet and level height of 15 feet, so its plan area is 375 square feet.
The four plan areas sum to 225 + 225 + 375 + 375 = 1200 ft². Multiplying each by the common factor and adding the surfaces gives the same 1341.64 square feet. This check is for the stated simple example. It is not a general ridge-length rule for every hip roof.
| Example plane | Projected area | Surface at 6:12 |
|---|---|---|
| End triangle A | 225 ft² | About 251.56 ft² |
| End triangle B | 225 ft² | About 251.56 ft² |
| Long trapezoid A | 375 ft² | About 419.26 ft² |
| Long trapezoid B | 375 ft² | About 419.26 ft² |
| Combined roof | 1200 ft² | About 1341.64 ft² |
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These rows use assumed sizes and derived, checked arithmetic. They are not observations of a home. A report's actual plane outline controls its measured area. Do not invent a ridge length just to make a real roof fit this example.
Why hip and gable areas can match
The roof's surface is steeper than its footprint by the slope factor. In the equal-pitch case, that factor is constant across all the planes. Whether the footprint is split into two rectangles or into triangles and trapezoids does not alter the sum. The plan has the same covered area before any ordering allowance.
A gable with the same sizes therefore has the same area. It usually has different eave, rake, ridge and hip details. Those are line lengths instead of roof-surface square feet. An area worksheet cannot turn them into extra product counts without the right sizes and product coverage.
The common claim that a hip roof always needs a fixed percent more material confuses net area with cuts. Diagonal edges can affect how covering pieces are cut and reused. That is a layout issue. A stated cuts allowance can differ even when the net surface agrees.
This also explains why the footprint should not be multiplied by four. Four faces do not mean four complete footprints. Each face covers only its own plan area. Counting the full rectangle once for each face repeats the same level space.
Separate surface, cuts and accessory quantities
Keep three records when you move from the area result to ordering. The first is net roof surface. The second is the field-covering order, including its explicitly chosen cuts allowance and package rounding. The third is the separate set of edge and junction products. Do not collapse them into one number called squares.
For asphalt shingles, hip and ridge caps use linear coverage. Starter strips have their own coverage. A field-shingle bundle label does not show cap output. The shingle calculator keeps those optional extra product counts separate from field bundles.
For metal, the hip edges create diagonal cuts. The metal roof material calculator handles single-length rectangular runs only. Its simple count is not an exact order for a hip roof. Do not enter a triangular end's bounding rectangle and treat every full-length panel as installed surface.
Tile, slate and wood also depend on exposure, overlaps and layout. Gross tile sizes are not installed area. The manufacturer's current documents define the product's actual coverage and system details. GAF's document library gives that evidence for its own roofing products; it does not show coverage for other brands or materials.
Unequal pitches and intersecting roofs
When the planes have different pitches, one common factor cannot describe them. The footprint still represents level plan area. But each part needs its own ratio. Enter those parts in the general roofing calculator or use an already measured surface total.
Unequal slopes can also move the ridge or junction lines. A simple photograph may show a roof that looks like a hip yet conceals an added valley. Record what is known about each plane. If a small addition has no measured pitch, leave that part not complete instead of assigning the main roof's pitch to it.
An L-shaped footprint cannot be turned into a simple rectangular roof merely by entering its outer length and width. The outer rectangle can contain uncovered space. The same error occurs when a report's garage sizes are entered along with a footprint that already includes the garage. Drawings should identify which areas are in each total.
For a mixed-pitch example, suppose one plan section is 600 square feet at 4:12 and another is 600 square feet at 8:12. Each receives its own factor. Their sum is about 1353.57 square feet. A guessed middle slope would create a different area. These inputs are assumed and illustrate why a common-pitch shortcut needs its stated limit.
Curved surfaces, changing slopes and joined planes need more detailed measure. The calculator does not model them. Neither adding a guessed waste allowance nor choosing a steeper pitch can repair an incorrect measured model. Correct the measure basis before pricing or ordering the roof.
Carry the result into a replacement estimate
The replacement estimator uses roof surface for an installed rate. Supply the measured surface, the material and the rate's actual scope. A hip roof can need more detail work than a simple gable. But this area tool does not assign a labor multiplier. A written proposal must identify any priced access, junction or cutting work.
If a proposal gives ordering squares, ask for net surface too. It may include field allowance and package rounding. Multiplying that purchase amount by a roof-surface installed rate can count the allowance twice. Keep the source's unit on the worksheet instead of assuming every square figure means the same thing.
The tool cannot determine whether the roof needs replacement. A whole-roof area measurement does not mean the whole roof needs work; a problem may be limited to one flashing detail. Read the roof lifespan and replacement guide if the scope is unsettled. Decide what work is being priced before calculating its quantities.
A printable hip-roof measurement record
Print the valid result with its inputs and method. Keep the eave sizes, common pitch and roof form check beside the area. Record whether the numbers were measured or assumed. The paper record should not appear to be a site inspection when it was only a sample budget exercise.
Record the report date and any excluded surfaces in your project file. A detached garage, porch or dormer may need a separate covering or quote. Compare the listed surfaces with the written proposal. Correct arithmetic does not make a total complete if a roof plane was omitted.
The result does not save a street address or create an indexable results URL. If you edit inputs, calculate again before printing. The previous result is hidden after an edit, so it cannot quietly keep old sizes beside new field entries. Keep a dated copy when you need to compare two measured scenarios.
Sources and method limits
Check a roof report against the area model
Read the report's plane map before using its total. Some reports show both the house roof and a shed. Others show only the main roof. Match each drawn section to the work scope. A number copied from the cover sheet can hide those limits.
Check the pitch list next. If every face has the same slope, the simple footprint model can act as a cross-check. If a face has a different slope, use its own measured area. Do not alter the report to force agreement with this form. Find which input basis differs first.
An area gap can come from eave sizes. The walls sit inside the roof's edges. A plan measured at the walls can miss the overhang strip around the whole building. Enter eave sizes once, then keep that basis on the print record. Adding overhang to an already measured eave footprint would overstate the roof.
Use the report's unrounded figures when checking the sums. Displayed plane areas may be rounded even when the report's total uses greater precision. A small rounding difference is not the same as an omitted roof face. Keep both the plane map and the source total rather than changing one to force a match.
The final area also needs a scope label. A sound figure can describe the main roof alone. If the quote covers the garage too, add its verified surface as a separate line. That keeps what each number measures and prevents the site-wide total from replacing the exact work-area basis.
The roofing-square basis is checked against GAF's measurement guide. The equal-pitch area identity is derived and checked from separate plan areas and the right-triangle factor. Formula version 2.0 was checked October 14, 2026. No raster photograph supplies numeric evidence.
The method page records the equations and worked checks. Report an error through Contact and Corrections, including the mode, dimensions and expected result. Those inputs let us check the arithmetic without requesting your address or private contractor documents.
Frequently asked questions
What is a hip roof?
A hip roof has sloped planes descending toward eaves on every side. A simple rectangle has triangular ends and trapezoidal long sides. Actual houses can add valleys, dormers and unequal pitches. This calculator covers only the stated rectangular equal-pitch case, so the roof's name is not enough to check that its roof form fits.
Does a hip roof have more square footage than a gable roof?
With the same rectangular eave footprint and the same pitch on every plane, their net surface areas agree. The separate plane plan areas add to the same footprint and use one factor. Their cuts and extra product lengths differ. That can affect buying and work scope without adding a fixed percent to the net area.
Do I need the hip-rafter length for roof area?
Not for the simple equal-pitch rectangular area total. The footprint and common plane pitch find the surface factor. A framing or cut schedule needs more sizes and construction details, which this worksheet does not supply. Use the area result for covering counts; do not use it to choose timber lengths or framing connections.
Why does the form ask me to confirm equal pitch?
One common factor is valid only when every plane has that pitch. Unequal pitches need separate plan areas and their own factors. The check keeps the shortcut's assumption visible on the printed record. If the slope or roof form is unknown, obtain measured inputs instead of selecting the statement just to produce a total.
What allowance should I add for hip cuts?
The calculator does not choose one. Cuts depend on the covering, layout and how pieces can be reused. Keep any stated purchase allowance separate from net surface. Exact package or panel coverage must come from the selected system. A roof-surface installed rate should not automatically receive that purchase allowance a second time.
Can this calculate a hip roof with a porch?
Only if the entered rectangular eave footprint and common-pitch model truly covers the complete roof. A lower porch, joined valley or other slope usually needs its own measured section. Use separate planes in the general roofing calculator. Preserve the exclusions instead of stretching the main footprint to include an unknown addition.
Verdict: geometry first, ordering second
Use the hip roof calculator for a known rectangular equal-pitch roof. Its area formula does not infer cuts, extra product lengths or installed prices. Keep the roof form statement with the result. For varied roofs, return to the roofing calculator and work from separate measured planes.