How to use
- Choose a simple gable roof from horizontal dimensions or enter a known roof-surface area.
- For the gable method, enter the projected dimensions including the overhangs you intend to cover, and specify rise per 12 or percent grade.
- Enter a product’s useful coverage per pack and a project-specific allowance. Add a price for that same pack if known.
- Check net surface area, allowance, full packs, supplied area and rounding excess before checking the roof layout.
Calculation method
For a simple equal-pitch gable roof, surface area = horizontal footprint area × √(1 + slope ratio²), where slope ratio is rise / horizontal run. Known-area mode uses the entered roof surface directly. Required area adds the allowance. Pack count rounds required area up by the product’s useful coverage, and cost multiplies complete packs by the optional price. Roofing squares are displayed as an area conversion, not a new product unit or price basis.
Worked example
A 12 × 8 m horizontal footprint with 5:12 pitch has a factor of 13/12 and a net roof area of 104 m². A 10% allowance adds 10.4 m², making 114.4 m². Packs covering 3 m² require 39 packs, supplying 117 m². At 20 USD each the purchase costs 780 USD; 2.6 m² is pack-rounding excess beyond the allowance-adjusted target.
Assumptions and limits
The simple gable model does not measure hips, valleys, dormers or different pitches automatically. Useful product coverage may differ from nominal sheet dimensions because of laps or exposure. The tool does not select a roof system, fasteners, flashings, underlay or an installation allowance. It is a quantity estimate, not a structural or watertightness assessment.
Continue your plan
Cross-check slope with the roof pitch calculator, measured sections with the area calculator, and separate insulation quantities with the insulation calculator.
Copy, download or print a valid result to keep the inputs with the estimate. Currency selections label your prices; they do not apply an exchange rate. Product-dependent examples should be replaced with data for the material or equipment you actually use.
For the measurement and planning details, read converting roof footprint, pitch and pack coverage.