Plan a metal roof for a house, shop, barn or shed. Enter the building size, pitch and overhangs and choose a panel width to get the number of panels, the cut length to order, fasteners, ridge cap and trim.
Last updated:
Roof
Roof type
ft
ft
/12
Rise in inches per 12 in of run.
ft
Horizontal, past the wall.
ft
in
Drip into the gutter, often 1–2 in.
Panels and trim
in
70–80 is typical with purlins at 24 in.
in
Follow the manufacturer's wind-zone spacing.
ft
Pieces lap 6 in, so 10.5 ft covers 10 ft.
Prices (optional)
$/linear ft
$/piece
Enter your values to see the result.
Advertisement
Advertisement
How to use the Metal Roofing Calculator
Choose gable or shed and enter the building length along the eave and the width between the eave walls.
Enter the pitch and overhangs: eave overhang, rake overhang and how far panels extend past the eave.
Pick the panel type by coverage width, or enter a custom width and fastening system.
Read the panel count and cut length, then the fasteners, trim and closures.
Download the cut list and trim list to send with your order.
How metal roof panels are calculated
Pitch multiplier = √(1 + (pitch ÷ 12)²). It converts horizontal run into the length along the slope.
Panel length = (half the building width + eave overhang) × multiplier + extension past the eave. For a shed roof, the run is the full width plus the overhangs at both ends.
Trim: ridge cap = roof length; eave trim = roof length per slope; rake trim = 2 × panel length per slope.
Example: a 30 × 40 ft shop at 4/12 with 1 ft eaves, 6 in rakes and 36 in panels needs 16 ft × 1.054 = 202.4 in, + 1.5 in = 203.9 in → 17 ft 0 in panels, 41 × 12 ÷ 36 → 14 per side, 28 total, and 41 ft of ridge cap.
Pitch multipliers for metal roofs
Pitch
Multiplier
Panel length for 15 ft run (rounded up)
1/12
1.003
15 ft 1 in
2/12
1.014
15 ft 3 in
3/12
1.031
15 ft 6 in
4/12
1.054
15 ft 10 in
6/12
1.118
16 ft 10 in
8/12
1.202
18 ft 1 in
12/12
1.414
21 ft 3 in
Ordering tips
Measure the real roof before ordering cut-to-length panels. Walls are rarely perfectly square; measure the slope at both ends and in the middle.
Long runs: panels over about 40 ft are hard to ship and handle. Splice with an end lap of at least 6 in (exposed fastener) or use a step for standing seam.
Order a spare panel or two for mistakes and future repairs, plus touch-up paint and sealant tape.
Purlin spacing and screw patterns depend on panel gauge and wind zone. Follow the manufacturer's installation guide.
Frequently asked questions
How do I calculate how many metal roof panels I need?
Divide the roof length along the eave (building length plus both rake overhangs) by the panel's coverage width, not its overall width, and round up. That is the count for one slope; double it for a gable roof. A 40 ft building with 6 in rake overhangs is 41 ft = 492 in, and 492 ÷ 36 = 13.7, so 14 panels per side, 28 in total.
How do I find the length of metal roof panels?
Take the horizontal run of one slope (half the building width plus the eave overhang for a gable roof), multiply by the pitch multiplier √(1 + (pitch ÷ 12)²), and add any extension past the eave. For a 30 ft wide building at 4/12 with a 1 ft overhang: 16 × 1.054 = 16.87 ft (202.4 in), plus 1.5 in = 203.9 in, so cut panels at 204 in (17 ft 0 in).
How many screws do I need for a metal roof?
Exposed-fastener panels typically need about 70 to 80 screws per 100 sq ft with purlins at 24 in on center; closer purlins or high-wind zones need more. Standing seam uses concealed clips along each seam instead, often every 24 in or as specified by the manufacturer for your wind zone.
What is the difference between panel width and coverage width?
Panels overlap at the side lap, so a panel that measures about 38 in overall may cover only 36 in. Always use the coverage (net) width when counting panels.
How much does trim overlap?
Metal trim such as ridge cap, eave trim and rake trim is usually sold in 10 ft 6 in pieces and overlapped about 6 in, so each piece covers 10 ft. The calculator divides linear feet by the net length and rounds up.
Does this work for hip roofs?
Not exactly. Hip roofs need panels cut at angles on every hip, more trim and more waste. Use this tool for gable and shed roofs, or treat each rectangular section separately and add 10–15% extra panels for hip cuts.
What pitch does a metal roof need?
Many exposed-fastener panels are rated for slopes of 3/12 and above, while many mechanically seamed standing-seam systems are rated down to about 1/2:12 to 1/4:12. Check the minimum slope in the panel manufacturer's installation guide.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.