Roof area calculator
Open Roof area calculator on Happytails.ai. This view has the same page content and links, with explicit tool capabilities. Read the processing notes before using a tool.
Tool capabilities
{
"id": "roof-area-calculator",
"category": "calculators",
"built": true,
"requirements": "Building length and width up to 1,000 m (3,280.8 ft), overhangs from 0 to 5 m (16.4 ft), pitch from 0 to 48 per 12, 0 to 75 degrees or 0 to 400%, and up to 200 plane rows with counts from 1 to 100 in up to 100,000 characters. Calculated on your device; download a JSON report, a results CSV and a roof planes CSV.",
"implementation": {
"fields": [
{
"key": "mode",
"label": "Measure",
"value": "Building footprint",
"type": "select",
"values": [
"Building footprint",
"List of roof planes"
]
},
{
"key": "lengthUnit",
"label": "Length unit",
"value": "ft",
"type": "select",
"values": [
"ft",
"in",
"yd",
"m",
"cm",
"mm"
]
},
{
"key": "roofType",
"label": "Roof shape",
"value": "Gable",
"type": "select",
"values": [
"Gable",
"Hip",
"Shed"
],
"help": "Every plane has the same pitch. Use the plane list for mixed pitches, valleys or add-ons.",
"showWhen": {
"mode": [
"Building footprint"
]
}
},
{
"key": "length",
"label": "Building length, along the eaves",
"value": 40,
"type": "number",
"min": 0,
"step": "any",
"help": "Outside wall to outside wall, parallel to the eaves (the ridge direction on a gable roof).",
"showWhen": {
"mode": [
"Building footprint"
]
}
},
{
"key": "width",
"label": "Building width, across the slope",
"value": 30,
"type": "number",
"min": 0,
"step": "any",
"help": "Outside wall to outside wall, eave wall to eave wall.",
"showWhen": {
"mode": [
"Building footprint"
]
}
},
{
"key": "eaveOverhang",
"label": "Eave overhang, measured level",
"value": 1,
"type": "number",
"min": 0,
"step": "any",
"help": "Level distance from the wall to the fascia along the eaves. On a hip roof it applies on all four sides. Enter 0 for none.",
"showWhen": {
"mode": [
"Building footprint"
]
}
},
{
"key": "rakeOverhang",
"label": "Rake overhang, measured level",
"value": 1,
"type": "number",
"min": 0,
"step": "any",
"help": "Level distance from the gable or end wall to the rake edge. Enter 0 for none.",
"showWhen": {
"mode": [
"Building footprint"
],
"roofType": [
"Gable",
"Shed"
]
}
},
{
"key": "pitchFormat",
"label": "Pitch entered as",
"value": "Rise per 12 run",
"type": "select",
"values": [
"Rise per 12 run",
"Angle in degrees",
"Percent slope"
]
},
{
"key": "pitch12",
"label": "Rise per 12 units of run",
"value": 6,
"type": "number",
"min": 0,
"max": 48,
"step": "any",
"help": "6 means 6 units of rise for every 12 units of level run, a 6/12 roof. From 0 to 48.",
"showWhen": {
"mode": [
"Building footprint"
],
"pitchFormat": [
"Rise per 12 run"
]
}
},
{
"key": "pitchAngle",
"label": "Roof angle (degrees)",
"value": 30,
"type": "number",
"min": 0,
"max": 75,
"step": "any",
"help": "Angle of the roof surface above level, from 0 to 75 degrees.",
"showWhen": {
"mode": [
"Building footprint"
],
"pitchFormat": [
"Angle in degrees"
]
}
},
{
"key": "pitchPercent",
"label": "Slope (%)",
"value": 50,
"type": "number",
"min": 0,
"max": 400,
"step": "any",
"help": "Rise divided by run times 100, from 0 to 400.",
"showWhen": {
"mode": [
"Building footprint"
],
"pitchFormat": [
"Percent slope"
]
}
},
{
"key": "planes",
"label": "Roof planes",
"value": "plane, length, width, pitch, shape, count\nMain roof side, 42, 16, 6, rectangle, 2\nGarage roof side, 22, 12, 4, rectangle, 2\nGarage hip end, 24, 12, 4, triangle, 1",
"type": "textarea",
"maxLength": 100000,
"help": "One plane per line: name, plan length, plan width, pitch, then optional shape (rectangle or triangle) and count. Plan sizes are level and include overhangs.",
"showWhen": {
"mode": [
"List of roof planes"
]
}
}
],
"registrationFamily": "roof-and-cladding",
"input": false,
"live": false,
"presentation": "metrics",
"note": "Calculated on your device for buildings up to 1,000 m on a side, overhangs up to 5 m, up to 200 plane rows and pitches from 0 to 48 per 12, 0 to 75 degrees or 0 to 400%.",
"experience": {
"automatic": false,
"single": true,
"inputMaxLength": 1000000,
"inputMode": "text",
"label": "Roof measurements",
"placeholder": "Use the fields below",
"help": "This calculator uses the measurement fields only. Up to 1,000,000 characters. Review the settings before running.",
"helpParts": [
"This calculator uses the measurement fields only.",
"Up to 1,000,000 characters.",
"Review the settings before running."
],
"action": null
},
"mode": "explicit",
"interactive": false
},
"execution": "Browser interface",
"api": null,
"browser_agent": {
"supported": true,
"name": "run_current_tool",
"discovery": "WebMCP on the human page in a supporting browser",
"verification": "See audit/API-AUDIT.md; availability is not verification"
}
}Page guide
Turn a building footprint or a list of roof planes into sloped roof area and roofing squares. Overhangs, pitch and hip or gable shape are included, with eave, rake, ridge and hip lengths for ordering trim.
How to use Roof area calculator
- Choose a building footprint for a simple gable, hip or shed roof, or a list of roof planes for anything more complex.
- Enter the outside wall dimensions and level overhangs, or one plane per line with its plan length, width and pitch.
- Pick how the pitch is entered: rise per 12, an angle or a percent slope.
- Review the sloped area, squares and edge lengths, then download the JSON report or the CSV files.
Useful next steps
From plan area to sloped area
A flat roof plane covers more surface than its footprint. Its sloped area is the level plan area times √(1 + (rise ÷ run)²), which equals 1 ÷ cos(roof angle) (OpenStax Precalculus 2e, 5.4 Right Triangle Trigonometry, checked 16 October 2026). A 6/12 roof has a factor of 1.118034, so a 42 × 32 ft footprint with overhangs (1,344 ft²) has 1,502.64 ft² of roof.
Footprints and overhangs
Overhangs are measured level, from the wall to the fascia or rake edge. A gable or shed roof adds the rake overhang at both ends and the eave overhang on both long sides. A hip roof adds the eave overhang all round and puts the ridge along the longer side, so a 13 × 9 m hip footprint has a 4 m ridge and four hips. When every plane shares one pitch, the whole roof is the plan area times one factor.
Complex roofs, plane by plane
Fine Homebuilding recommends breaking a complex roof into rectangles and triangles (Mike Guertin, How to Estimate Materials for Roofing Projects, checked 16 October 2026). Enter each plane with its level length and width; triangles count half, and a trapezoid can be entered as a rectangle using the average of its two parallel sides. Each plane may have its own pitch.
Squares and limits
A roofing square is 100 ft² of roof surface (Wikipedia, Square (unit), checked 16 October 2026). Waste, starter and ridge cap are added in the roof shingle calculator. The estimate assumes flat planes and does not check structure, drainage or roofing code minimum slopes. Unit conversions use NIST SP 811 factors.