Metal Stud
Steel studs and track for interior partition walls below the roof.
OpenRoofing Calculator
Calculate the inclined roof area and number of metal panels needed for any roof pitch and panel size.
What this calculates
Calculates horizontal (plan) area, actual inclined roof surface, panels per row, number of rows and total panels required including waste allowance.
Formula used
Slope factor = √(1 + (pitch/100)²). Inclined area = length × width × slope factor. Panels per row = ceil(length ÷ useful width). Rows = ceil(inclined width ÷ panel length). Total = panels per row × rows × (1 + waste).
Worked example
An 8 m × 4 m roof at 20% pitch: slope factor = 1.020. Inclined area ≈ 32.6 m². With 0.85 m useful width and 3.66 m panels: 10 panels/row × 2 rows = 20 panels base. With 10% waste: 22 panels.
Typical pitch values
15–20% (9–11°): low-slope metal roofs. 25–35% (14–19°): standard residential. 40–60% (22–31°): steep residential or alpine. Below 15% requires special waterproofing detailing.
When not to use this calculator
Hip roofs, valley sections, complex multi-slope roofs or curved roofs require separate area calculations for each face. This calculator handles one rectangular slope.
How to use this calculator
- Enter the plan (horizontal) dimensions of the roof section — length and width as measured on the ground plan, not on the slope.
- Enter the roof pitch as a percentage — a 20% pitch means the roof rises 20 cm for every 100 cm of horizontal run (≈ 11°).
- Enter the useful panel width — for corrugated metal sheets this is typically 0.85 m for a 1.0 m wide sheet (side overlap reduces usable width).
- Enter the panel length — standard corrugated sheets are 2.44 m, 3.05 m or 3.66 m.
- Click "Calculate roofing" to get inclined area, panel count and grid layout.
Converting pitch formats
Roof pitch is expressed differently worldwide. The formula in this calculator uses percentage. To convert:
- Percentage to degrees: angle = arctan(pitch / 100). A 20% pitch = arctan(0.20) ≈ 11.3°.
- X:12 (US format) to percentage: (X ÷ 12) × 100. A 4:12 pitch = 33.3%. A 6:12 pitch = 50%.
- Degrees to percentage: tan(angle) × 100. A 15° pitch = tan(15°) × 100 ≈ 26.8%.
- Minimum slope for metal roofing: Most manufacturers require at least 5–10% (3–6°) for concealed-fastener panels and 15–20% for exposed-fastener corrugated profiles. Below minimum slope, water infiltrates at end laps.
Structural design notes
This calculator provides panel quantities only. The structural elements — rafters, purlins, trusses and connections — must be designed for snow, wind and self-weight loads by a structural engineer or comply with pre-engineered system specifications. In seismic zones, roof-to-wall connections require specific detail. Check local building codes before finalizing any roof structure.
Frequently asked questions
How do I calculate roof area with pitch?
Multiply the plan area by √(1 + (pitch%)²/10000). For 20% pitch: factor ≈ 1.020. For 30%: factor ≈ 1.044.
How many roofing sheets do I need?
Divide inclined area by net coverage per sheet and round up. Add 10% for cuts and overlaps.
What is a typical roof pitch?
20–30% is common for corrugated metal roofing. Check local codes for minimum pitch requirements for your panel type.
Does this include ridge caps and flashings?
No. Add ridge caps, flashings and eave trims based on your ridge and hip lengths separately.
Assumptions
- One rectangular slope (half the roof). For a gable roof, double the panels.
- Useful panel width accounts for overlap (typically 0.85 m for a 1.0 m wide sheet).
- Waste covers cuts, ridge overlaps and edge trims.
- Does not include ridge caps, flashings, purlins or fixings.
Technical warning
Structural elements (purlins, rafters, trusses) must be designed for the expected loads. Always comply with local building codes and manufacturer installation specifications.
Common mistakes
- Forgetting to double the panel count for a symmetrical gable roof.
- Using total panel width instead of useful (net) width.
- Not accounting for ridge cap overlap at the top.
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