Roofing Calculator
Roof area, panels or packs, underlayment, ridge, edge and cost.
| Order item | Whole units | Cost |
|---|---|---|
| Roof panels | 25 pcs | — |
| Underlayment rolls | 2 pcs | — |
| Ridge and hip units | 6 pcs | — |
| Edge / drip-edge pieces | 24 pcs | — |
How it works
Overhangs are added to the rectangular building plan before the pitch factor is applied. Roof area equals horizontal plan area divided by cosine of the pitch. A gable has two rectangular planes, a shed has one, and a hip roof uses the same uniform-pitch area factor with its ridge and four hips calculated separately.
Coverage products divide allowance-adjusted area by the effective area on one bundle, pack or roll. Rectangular gable and shed planes count panel columns and rows from effective dimensions; hip panels fall back to area because their cuts need a layout. Underlayment, ridge/hip units and edge pieces use their own effective coverages.
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How the Roofing Calculator works
This roofing calculator turns a rectangular building plan, overhangs and pitch into actual sloped area. It handles gable, shed and hip geometry, orders the covering by packs or effective panel dimensions, and adds underlayment, ridge and hip caps, edge trim and optional cost.
Plan area is not sloped roof area
Overhangs are added to both ends of the building length and both eave sides of its width. The horizontal plan is then divided by cosine of the pitch: increasing pitch lengthens the slope and raises material area. A gable can be viewed as two rectangles, while a shed roof is one full-width inclined plane.
A uniform-pitch hip roof uses the same area factor. Its main ridge is the difference between the long and short plan dimensions, and its four sloping hips are calculated separately for cap material.
Enter pitch as an angle or rise over run
Degree mode uses the geometric roof angle. Rise over run describes the same triangle: a 6:12 pitch climbs six units for every twelve horizontal units, which is about 26.6 degrees.
The geometry assumes a rectangular plan and one constant pitch. Dormers, valleys, additions, broken slopes and wall intersections must be separated into their own planes and added to the purchasing layout.
Effective coverage controls the order
For shingles, tiles, membranes or another coverage product, enter the effective area from one pack after required laps. Panel mode uses effective width and length: rectangular gable and shed planes round to complete columns and rows before the allowance is added.
Hip planes are triangular and trapezoidal, so an exact sheet count needs a cutting drawing. Panel mode therefore falls back to effective area for a hip roof and labels the result as an estimate.
Accessories remain separate products
Underlayment rounds by effective roll area, ridge and hip products by effective linear coverage, and edge trim by roof perimeter and usable piece length. Each optional unit price remains visible instead of being hidden inside one notional covering rate.
The result does not design rafters, battens, ventilation, drainage, fasteners, penetrations or flashing details. Those quantities depend on the approved roof assembly and structural design.
FAQ
What is the area of a 10 × 8 m gable roof? expand_more
With 0.3 m end overhangs, 0.5 m eave overhangs and a 30° pitch, the roof plan is 10.6 × 9 m. Dividing by cos 30° gives about 110.16 m² across both slopes before the allowance.
What does a 6:12 roof pitch mean? expand_more
The roof rises six units for every twelve horizontal units. The ratio is 0.5, arctan(0.5) is about 26.6°, and sloped area is 1.118 times horizontal projected area.
Why is a hip-roof panel count approximate? expand_more
Its planes are triangles and trapezoids, and usable offcuts depend on panel direction and the cutting sequence. Area plus allowance is useful for planning, but an exact sheet order requires a drawing of every plane.
Does the result include roof framing? expand_more
No. It estimates covering geometry and selected purchasing units. Rafter size and spacing, battens, fasteners, ventilation and structural loads belong to the roof design.