This barndominium metal roof and wall panel calculator turns your building size, pitch and openings into roof and wall area, panel counts and lengths, trim and fastener rules of thumb. Use it to check a builder's material list, not to replace the supplier's takeoff.
Planning estimate only. The panel supplier's takeoff and your engineer's plan set the real order.
En español: Calculadora de paneles metálicos para techo y paredes de barndominium
Panels (whole panels, before waste)
| Item | Count | Length each |
|---|
Areas, trim and fasteners
| Item | Amount |
|---|
Example with this calculator's defaults except openings set to zero: 14 ft eaves and 36-inch panels.
How to use it in four steps
- Take sizes from your plan
Use outside building length and width, eave height and the pitch noted on the roof plan.
- Match the panel
Enter the coverage width from the spec sheet and the overhang from the elevations.
- List the openings
Count each door and window size from the door and window schedule. Group same sizes.
- Compare with the bid
Put your numbers next to the builder's or supplier's list and ask about any gap over about 10%.
How to read a builder's material list
| Line on the list | What to check |
|---|---|
| Roof panels | Count and length should be close to the table above. Ask if it includes the overhang. |
| Wall panels | Sidewalls are a single length; gables vary. Ask how openings were handled. |
| Ridge, eave and rake trim | Compare linear feet. Missing trim is a common surprise. |
| Screws and closures | Ask for the fastener pattern and whether foam closures are included. |
| Gauge and finish | Which gauge, which coating and which paint warranty, in writing. |
This is for checking, not ordering: real panel counts come from the supplier's takeoff for the exact profile, side laps, trim and cut-offs. A bid that is far from these numbers is a reason to ask a question, not proof of an error.
Questions about gauge, wind and hail
- Which gauge is in the bid? A lower number is thicker steel, so 26 gauge is thicker than 29. Ask for it in writing and for the price difference.
- What is the wind-uplift rating? Ask for the test data for the exact panel (for example ASTM E1592) and the fastener pattern it assumes.
- Who set the design wind? The engineer's plan, not the panel brochure, decides the fastening for your site.
- Is it exposed-fastener or standing seam? The screw count here fits exposed-fastener panels; standing seam uses clips.
- What about hail and insurance? Ask your insurer if panel gauge or roof type changes your rate. See our hail, tornado and wind history for Smith County and the barndominium insurance guide.
The formulas this page uses
| Quantity | Formula |
|---|---|
| Slope factor | sqrt(1 + (pitch / 12)^2) |
| Rafter and panel length | (half width + overhang) x slope factor, up to the next inch |
| Roof area | 2 x (length + 2 x overhang) x rafter length |
| Roof panels per side | (length + 2 x overhang) x 12 / coverage, rounded up |
| Wall area | Sides plus ends, plus a gable triangle at each end (width x rise / 2, rise = half width x pitch / 12) |
| Trim | Ridge = length + 2 x overhang; eave = 2 x that; rake = 4 x rafter length |
Pair this with the gutter and downspout calculator, the spray foam insulation calculator and our guide to insulation and condensation under metal roofs. For doors and windows see windows, doors and garage doors.
We are a referral service that connects you with independent local builders; we do not sell or install metal panels. Use the form below to request quotes, then read how to choose a barndominium builder.
Frequently asked questions
How do you figure metal roof panels for a barndominium?
Find the rafter length: half the building width plus the eave overhang, times sqrt(1 + (pitch/12)^2). Panels run eave to ridge, so each panel is that long, rounded up to the next inch. The count per side is the building length plus both gable overhangs, divided by the panel coverage width, rounded up. Double it for a two-slope gable roof.
How long are the roof panels?
For a 40 ft wide building at 4/12 with a 1 ft overhang, the rafter length is about 22.14 ft, so the panels are about 22 ft 2 in. A steeper pitch or bigger overhang makes them longer. Ask your supplier for its longest panel and whether a long run needs a splice.
How many screws does a metal roof need?
The calculator uses about 80 screws per 100 sq ft for roofs and about 70 per 100 sq ft for walls. These are common rules of thumb for exposed-fastener panels. The real number depends on the panel profile, the purlin or girt spacing and the fastener pattern in the manufacturer's instructions. Standing seam roofs use clips instead.
Does the panel count take the doors and windows out?
No. Wall area is reduced by the openings you list, but the panel counts are not, because panels beside and above openings are still cut and ordered. Your supplier's takeoff will say how many panels can be saved.
Should I choose 26 or 29 gauge panels?
Gauge is steel thickness, and a lower number is thicker steel, so 26 gauge is thicker than 29. Ask your builder which one is in the bid, what the panel's wind-uplift rating or test data is, and what fastener pattern that rating assumes. We do not give numbers because they depend on the manufacturer.
Why does my supplier's count differ from this page?
Suppliers account for the actual panel profile, side laps, trim pieces, how walls are broken at doors, and cut-offs. Our numbers are geometry only. A small gap is normal; a large one is worth a question.