Metal Roof Calculator
Reviewed by the My Roof Pitch editorial team · Updated · Free, no sign-up, works offline after first load
Panel count is the eave length divided by the panel's net coverage width, rounded up. Panel length is the run times the pitch multiplier plus the overhang. A 40 ft eave with 36 in panels needs 14 panels per slope, at roughly 80 screws each.
Your measurements
Enter the values you know — results update live.
Measured horizontally along the eave, including gable overhangs.
Plan distance from the eave to the ridge, not the slope distance.
Standing seam works down to 0.25:12; exposed fastener panels need 3:12.
The width each panel covers after the side lap — usually 36 in for exposed fastener, 16 in for standing seam.
Two for a gable roof, one for a shed roof.
Analysis
Live results from your measurements.
Show the working
- Panels per slope:
ceil(40 ÷ 3)= 14 - Panel length:
14 × 1.0833 + 0.17= 15.33 ft - Total panels:
14 × 2= 28 - Roof area:
40 × 15.33 × 2= 1,227 sq ft - Screws:
1,227 × 0.8= 982 - Total weight:
1,227 × 0.9= 1,104 lb
What this calculator does
Metal roofing is ordered as panels cut to length, so the two numbers that matter are how many panels fit across the eave and how long each one has to be. Panel width is quoted two ways: the physical width of the sheet and the net coverage width after the side lap. Always calculate against net coverage. Panel length is the slope distance from eave to ridge plus a small drip overhang, and most suppliers cut to the exact length you specify, which removes almost all field waste.
How to use it
- Measure the eave length of one slope horizontally, including gable overhangs.
- Divide by the panel's net coverage width and round up to get panels per slope.
- Measure the horizontal run from eave to ridge.
- Multiply the run by the pitch multiplier to get the slope distance.
- Add the drip overhang to get the panel length to order.
- Multiply panels per slope by the number of slopes for the total.
The formula
Panels per slope
panels = ceil(eave length / net coverage width)
Net coverage width already accounts for the side lap between panels.
Panel length
panel length = run × pitch multiplier + overhang
The slope distance, plus a small projection past the fascia for the drip edge.
Screw count
screws = roof area × 0.8
Roughly 80 fasteners per square for exposed-fastener panels at 24 in purlin spacing.
Worked example
A 48 ft long barn, 16 ft run per slope, 4:12 pitch, 36 in coverage panels, two slopes, steel at 0.9 lb per sq ft.
- Panels per slope: 48 ÷ 3 = 16
- Multiplier for 4:12: 1.0541
- Panel length: 16 × 1.0541 + 0.17 = 17.03 ft
- Total panels: 16 × 2 = 32
- Area: 48 × 17.03 × 2 = 1,635 sq ft
- Weight: 1,635 × 0.9 = 1,472 lb
32 panels cut to 17 ft 1 in, covering 1,635 sq ft, with about 1,308 screws and 1,472 lb of steel.
Reference chart
| Eave length | 16 in coverage | 24 in coverage | 36 in coverage |
|---|---|---|---|
| 20 ft | 15 | 10 | 7 |
| 30 ft | 23 | 15 | 10 |
| 40 ft | 30 | 20 | 14 |
| 50 ft | 38 | 25 | 17 |
| 60 ft | 45 | 30 | 20 |
Metal roofing systems compared
| System | Minimum pitch | Typical coverage | Fastening |
|---|---|---|---|
| Standing seam | 0.25:12 | 16–18 in | Concealed clips |
| Exposed fastener (R-panel) | 3:12 | 36 in | Screws through the panel face |
| Corrugated | 3:12 | 24–36 in | Screws through the crown |
| Metal shingle / tile profile | 3:12 | varies | Clips and nails |
| Stone-coated steel | 3:12 | varies | Battens and nails |
Common mistakes
- Using the physical panel width instead of the net coverage width — that under-orders by about 8%.
- Measuring the run and ordering that as the panel length. The panel follows the slope, which is always longer.
- Specifying exposed-fastener panels below 3:12, where they are not approved.
- Forgetting closure strips, which are required at the eave and ridge on corrugated profiles.
- Ignoring thermal movement on long panels. Runs over about 30 ft need floating clips.
- Under-ordering trim. Ridge, rake, valley and eave trim are all separate line items.
Assumptions and limits
- Rectangular roof planes with panels running straight from eave to ridge.
- Panel coverage width is the net figure after side laps.
- Screw density reflects 24 in purlin or batten spacing.
- Panel weight is entered per square foot of roof area; verify with the manufacturer's data sheet.
- Trim, closures and underlayment are quantified separately.
Frequently asked questions
How many metal roofing panels do I need?
Divide the eave length by the panel's net coverage width and round up. A 40 foot eave with 36 inch coverage panels needs 14 panels per slope, so 28 for a simple gable roof.
How long should metal roof panels be?
Panel length equals the horizontal run times the pitch multiplier, plus 1.5 to 3 inches of drip overhang. A 14 foot run at 5:12 needs panels about 15 feet 2 inches long.
How many screws per square of metal roofing?
About 80 screws per square, or 0.8 per square foot, for exposed-fastener panels on 24 inch purlin spacing. Standing seam uses concealed clips instead, typically one clip per 24 inches per seam.
What is the minimum pitch for a metal roof?
Standing seam with sealed seams is approved down to 1/4:12. Exposed-fastener and corrugated panels need at least 3:12 under the IRC because their laps rely on gravity drainage.
Is metal roofing measured in squares?
Metal is priced per square foot or per linear foot of panel more often than per square, but the underlying area calculation is identical to any other roofing material.
Do metal panels need underlayment?
Yes. A synthetic high-temperature underlayment is standard, and ice and water shield is required at eaves and valleys in cold climates. Metal directly on bare deck will condense.
Related guides
- Minimum Roof Pitch by Material: IRC Limits for Every CoveringEvery covering has a slope below which water gets under it. Here are the code minimums, the underlayment upgrades that unlock them, and what to use when your roof is too flat.
- Metal Roof Pitch: Minimums, Panel Lengths and Cost by SlopeMetal covers a wider slope range than any other roofing, but only if you match the profile to the pitch. Minimums, panel take-off, weight and the cost curve across slopes.
- Roof Replacement Cost: How Roofing Quotes Are Actually BuiltRoofers price per square, not per square foot of house. Here is how material, labour, tear-off, steepness and access combine into the number on your quote — and where the extras hide.
Last updated 2026-08-05. Results are estimates for planning and are not a substitute for a licensed engineer or local code review.