Does the calculator include ridge caps and flashings?

No. Ridge caps, hip flashings, valley flashings and eave trims are not included. Add these separately based on the ridge and hip lengths.

Roofing Calculator

Q: How do I calculate roof area with pitch?

Multiply the plan (horizontal) area by the slope correction factor: √(1 + (rise/run)²). For a 20% pitch the factor is about 1.02, meaning a 10 m² plan area becomes roughly 10.2 m² of actual roof surface.

Q: How many roofing sheets do I need?

Divide the inclined roof area by the net coverage per sheet (width × length). Round up and add 10% for waste, cuts and overlaps.

Q: What is a typical roof pitch?

A 20–30% pitch (roughly 11–17°) is common for metal roofing. Steeper pitches shed water faster but require more panels. Check local building codes for minimum pitch requirements.

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.

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.