Steel Roofing Calculator

Roof mode

Units

Pitch input

Use Multi-slope to add multiple rectangular sections and shared hips/valleys. Per‑section orientation overrides are supported.

Geometry — Single Roof

Building length m

Building width m

Gable overhang (each) m

Eave overhang m

Waste allowance (%)

Geometry — Multi-slope Sections

Add rectangular roof sections. Each section has two slopes; totals are summed.

#	Length m	Width m	Pitch	Value	Orientation	Gable ovh m	Eave ovh m

Panels, Underlayment & Costs

Global panel orientation

Used for Single mode and as default in Multi.

Panel effective width mm

Panel max length m

0 = ignore splicing limit.

End-lap overlap mm

Screw mode

Underlayment roll coverage

m²

Underlayment overlap (%)

Screws per m²

Trim piece length m

Trim lap per joint m

Hip/Valley plan length m (total)

Or use the Intersections table below.

Hip/Valley pitch value

Hip/Valley pitch mode

Hip/Valley flashing cost per m

Skylights count

Skylight width m

Skylight height m

Other deduction area

m²

Chimneys, vents, etc.

Include gutters and downspouts

Gutter cost per m

Downspouts count

Cost per downspout

Panels cost per m²

Trim cost per m

Screws price per 100

Underlayment price per roll

Labor rate per m²

Labor productivity (m²/hour)

Crew size

Currency symbol

Profit margin (%)

Sales tax (%)

Tip: results show in both metric and imperial.

Intersections — Hips & Valleys (Optional)

Add individual hip/valley lines to refine flashing length and cost.

#	Type	Plan length m	Pitch mode	Value	Waste add-on (%)

Results

Item	Metric	Imperial	Notes
Enter values and click Calculate.

Example Data Table

Illustrative sizing for common sheds and garages; adjust to suit.

Building (L × W)	Pitch	Panel width	Approx. roof area	Panels (total)	Screws
12 m × 8 m	6:12	914 mm	~220 m²	~28	~2,900
40 ft × 30 ft	4:12	36 in	~2,300 ft²	~34	~2,800

Formulas Used

Single section: run = width / 2; rise_total = run × slope
Rafter length (no overhang) = √(run² + rise_total²)
Rafter length (with overhang) = previous + eave_overhang
Roof area = 2 × length_effective × rafter_length
Vertical orientation: panels_per_side = ceil(length_effective / panel_effective_width)
Horizontal orientation: rows_per_side = ceil(rafter_length / panel_effective_width)
Splicing: segments = ceil(primary_length / (max_len − end_lap))
Pieces with lap: N = ceil((length + lap) / (piece_len − lap))
Underlayment rolls = ceil( area / (roll_cov × (1 − overlap%)) )
Screws by area = ceil( area × screws_per_m² )
Hip/Valley true-length factor F = √(2 + slope²), where slope = rise/12 or tan(°)

Reference Data

Common Panel Profiles & Effective Coverage

Profile	Effective width	Typical sheet thickness	Notes
5‑Rib / AG Panel	914 mm (36 in)	0.45–0.6 mm	General purpose; barns, sheds, garages.
Corrugated 32/1000	1000 mm (39.37 in)	0.4–0.6 mm	Lightweight; high overlap flexibility.
Standing Seam (snap‑lock)	406 mm (16 in)	0.6–0.8 mm	Low exposed fasteners; premium finish.
Standing Seam (mechanical)	305 mm (12 in)	0.6–0.8 mm	High weather resistance; steeper learning curve.

Example Fastener Layouts (Area Mode Approximation)

Guidance only. Follow manufacturer data and local code for final design.

Exposure	Screws per m²	Approx. screws per ft²
Sheltered	10	0.93
Normal	12	1.12
Exposed / High wind	16	1.49

Sheet Thickness vs Approximate Weight

Thickness (mm)	Weight (kg/m²)	Weight (lb/ft²)
0.40	3.14	0.64
0.45	3.53	0.72
0.50	3.93	0.80
0.55	4.32	0.88
0.60	4.71	0.96
0.70	5.50	1.13

Hip & Valley Allowance

Approximate extra length and waste for diagonal hips/valleys on rectangular roofs with 90° corners. Assumes panels run eave to ridge.

Hip/Valley True-Length Factor by Pitch

True diagonal rafter length per unit common run: F = √(2 + (pitch/12)²)

Pitch (rise:run)	True-length factor F	Suggested cut waste add‑on	Notes
2:12	1.4283	5–7%	Shallow; fewer offcuts
3:12	1.4577	5–7%	Shallow; fewer offcuts
4:12	1.4907	7–10%	Moderate slope
5:12	1.5260	7–10%	Moderate slope
6:12	1.5635	7–10%	Moderate slope
8:12	1.6441	9–12%	More offcuts from angles
10:12	1.7321	10–15%	Steep; higher scrap
12:12	1.8257	10–15%	Steep; higher scrap

Quick Allowance Tips

Multiply the plan hip/valley length by F to get true slope length.
Add the waste add‑on to panel counts along the hip/valley zone.
Increase allowance for complex intersections, staggers, or brittle coatings.

FAQs

It is the net coverage of a panel after side-lap overlap is deducted. Manufacturers specify an “effective” or “cover” width for each profile.

Yes. Choose “horizontal” orientation to count rows along the slope. Cost and area remain consistent; counts adjust to orientation.

If the primary length exceeds your maximum panel length, we split panels into segments and add end-lap overlaps per joint to size and counts.

Fasteners depend on profile, purlin spacing, wind zone, and local codes. Use area mode for quick budgets or purlin mode for closer engineering.

Yes. We deduct opening areas from panel area, underlayment, labor, and screw counts. We also add flashing perimeter cost automatically.

Enable the checkbox to include both eaves as gutter length, plus downspout counts and costs in the financial summary.

No. The calculator applies your labor, margin, and sales tax if entered. Add delivery or special charges separately in your quote.

Geometry — Single Roof

Geometry — Multi-slope Sections

Panels, Underlayment & Costs

Intersections — Hips & Valleys (Optional)

Results

Example Data Table

Formulas Used

Reference Data

Common Panel Profiles & Effective Coverage

Example Fastener Layouts (Area Mode Approximation)

Sheet Thickness vs Approximate Weight

Hip & Valley Allowance

Hip/Valley True-Length Factor by Pitch

Quick Allowance Tips

FAQs

What does panel effective width mean?

Can I orient panels parallel to the ridge?

How do splices and end laps change counts?

How accurate is the fastener estimate?

Do openings reduce underlayment and screws too?

Can I include gutters and downspouts?

Do costs include local taxes or delivery charges?

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