How many purlins for a 40x60 metal building?
A full framing, sheeting, and trim takeoff for a 40' × 60' weld-up building: 12' eave, 4:12 pitch, one walk door, one 10'×10' roll-up door. Generated by Gable Takeoff; every number below is a real output, not a rounded guess.
Prices as of September 2026.
The math
- 1. Roof slope length
- Half the 40' width run up a 4:12 pitch works out to a slope length of 21' 1" per side — the 6' 8" of rise over a 20' run, with the slope itself as the hypotenuse.
- 2. Purlin lines per slope
- At 48" on-center spacing, that slope needs enough lines to keep every gap at or under 48" — 6 lines per roof slope, not counting the eave strut and ridge.
- 3. Bay count along the depth
- The building's 60' depth splits into 2 bays of 30' 0" — inside the standard steel stock length, so each purlin run is a single 30' stick with no splice.
- 4. Purlin lines × bays
- Across both slopes of a gable roof that totals 24 roof purlins, each a 10" member (sized off the same span chart as the wall girts), each 30' long.
- 5. Eave struts, separately
- The eave line itself gets its own member — 10", 30', 4 total, one per bay per side. These aren't counted in the 24 above.
What changes this number
Any of these shifts the purlin count for a "40x60":
Pitch
- A steeper pitch means a longer slope length, which can push the line count up
Purlin spacing
- Tighter on-center spacing (e.g. 36" instead of 48") adds more lines per slope
Single slope vs. gable
- A single-slope roof runs the full width in one plane instead of splitting at a ridge — different purlin geometry entirely
Span charts behind these sizes
The highlighted rows set this building's sizes: a 40' clear span calls for W12x19 frames, and 30' bays call for 10" roof purlins. These are the app's default charts.
Main frame · gable
| Clear span up to | Beam |
|---|---|
| 30' | W12x14 |
| 40' | W12x19 |
| 50' | W16x26 |
| 60' | W18x35 |
Purlins & wall girts
| Bay span up to | C-section |
|---|---|
| 20' | 6" |
| 25' | 8" |
| 30' | 10" (roof only) |
Adjust them for your climate. Snow and wind loads vary by region, so every row is editable on the app's Settings tab. Change a size or a span break to match what your engineer or local code requires, and every new estimate uses your charts. More about span charts
The short answer
24 roof purlins at 10" × 30', plus 4 eave struts at the same size. Change the pitch, the spacing, or the roof type and that number moves — run your own to see it.
Common questions
- How many purlins does a 40x60 metal building need?
- 24 roof purlins, plus 4 eave struts, for a 40x60 gable building with the default 12' eave, 4:12 pitch and 48" purlin spacing.
- What size purlins does a 40x60 use?
- 10" C-section in 30' sticks. The purlin chart sizes them by the span between frames, and a 60' building splits into bays of 30' 0".
See it before you order it
This same 40x60 draws itself in the app. Pick your wall, roof, trim, door, and wainscot colors and the building repaints in 3D; switch to the wireframe to check where the purlins, girts, eave struts, and jamb purlins land. Eight views — four isometric corners and four straight-on elevations — so you can look at a door from outside or the framing from the corner you'll erect from.
Change any dimension and get your own real takeoff.