Roof Calculator
Construction & MeasurementAccurate online roof pitch, surface area, metal sheet count, and cost estimation
4 Roof Types
Gable, hip, shed, mansard
Sheet Estimator
With overlaps & waste allowance
2D & 3D Model
Interactive live preview
01Choose a roof
02Building dimensions
Outer wall dimensions, excluding overhangs.
03Roof geometry
Overhangs are measured horizontally. H is above the wall top.
04Roofing material
Overlap and allowance
Material settings are examples. Confirm them with your supplier.
The result updates as you change settings.
Including eaves and gables
Includes 10% waste allowance
Sheets, trims, and fasteners
Materials needed
Including 10%Geometry and an indicative material order. Excludes rafters, battens, insulation, drainage, labor and delivery.
How to use the roof calculatorFrom building measurements to a material list
The calculator provides a preliminary estimate of roof geometry, coverage area and key roofing materials. Use dimensions measured along the outside of the walls.
- Choose a gable, hip, shed or mansard roof.
- Enter the building length and width without roof overhangs.
- Set the pitch or ridge height. The corresponding value is calculated automatically.
- Enter eave and gable overhangs, then confirm the usable dimensions of the roofing sheet.
- Set overlap, allowance and screw consumption according to the manufacturer's guidance.
- Review the Drawing, Materials and Estimate tabs and add your supplier prices.
Measure the building again and confirm the cutting plan with your supplier before ordering.
How the roof is calculatedGeometry, materials and allowance
Roof area is the sum of all slope areas, including horizontal overhangs. For a gable roof, slope length is derived from the pitch or ridge height and multiplied by the building length plus gable overhangs.
Shed, hip and mansard roofs use separate geometry models. The upper and lower sections of a mansard slope are calculated independently from their pitches and break point.
Sheet quantity uses the usable sheet width and lengthwise overlap. The result is rounded up to whole sheets before the selected allowance is added.
Ridge and hip trims use 2 metre sections with a 0.1 metre overlap. Screw quantity is based on covered area and the selected consumption per square metre.
Simplified gable-roof area formula:
S = 2 × (A + 2g) × (B/2 + e) / cos αA is building length, B is width, e is eave overhang, g is gable overhang and α is roof pitch. Intermediate values are not rounded.
Roof calculation FAQAccuracy, materials and limitations
How accurate is the online roof calculator?
The geometry is suitable for preliminary estimates when the input measurements are correct. The final order depends on sheet profile, cutting layout, junctions and manufacturer requirements.
Are overhangs included in building length and width?
No. Enter dimensions along the outside walls. Eave and gable overhangs are separate inputs and are added automatically.
How much material allowance should I use?
A simple rectangular gable roof often needs 7–10%. Hip and mansard roofs, diagonal cuts and many junctions may require 12–20% after consultation with the supplier.
Does the calculation reuse offcuts?
No. It uses a conservative layout and does not transfer offcuts between slopes. Exact optimization requires a cutting plan for the selected product.
What is excluded from the estimate?
Rafters, battens, membranes, insulation, drainage, complex flashing, delivery and installation work are excluded.
Can I save or share a calculation?
Yes. Saved calculations remain in this browser, while Share creates a URL containing the parameters for another device.
Does this replace a structural roof design?
No. It estimates covering geometry and materials but does not verify snow loads, wind loads, rafter sizes or structural capacity. Consult a qualified designer.