How this instrument works
A hoop house — also called a high tunnel or Quonset-style greenhouse — is built from a row of bent-pipe arches, or hoops, covered in plastic sheeting to create a season-extending growing space. This calculator answers the two questions every builder asks first: how many hoops do I need for a given length, and how much cover material does the semicircular roof and sidewalls actually require.
Hoop count comes from spacing arches evenly along the house's length: hoops = floor(length ÷ spacing) + 1, the same logic used for fence posts — you need one more hoop than the number of gaps between them. Cover area treats each hoop's cross-section as a semicircle, so the arch length per hoop is half a circle's circumference (π × radius), and total cover area is that arch length times the house's overall length — the sides-plus-roof surface a single sheet of poly or fabric has to span.
This is a geometry estimate, not a materials list: it deliberately excludes the end-wall triangles or rectangles at each end of the house, and it doesn't add allowance for wiggle-wire channel, purlins, baseboards, or overlap where sheets of covering join. Real hoop houses typically buy cover material oversized on every dimension to allow for ground-burial or securing at the base — treat the cover-area figure here as the bare geometric minimum, not a shopping-list number.
- Enter House length (ft) — the full run of the hoop house from end to end.
- Enter House width (ft) — this doubles as the hoop diameter, since each hoop spans the full width.
- Enter Hoop spacing (ft) — the on-center distance between adjacent hoops, commonly 4 ft for typical snow and wind loads.
- Read Hoops needed and Cover area (sides + roof only) — remember this excludes end walls and any overlap allowance.
Worked example — a 48×14 ft hoop house
Set House length to 48 ft, House width to 14 ft, and Hoop spacing to 4 ft. Hoops needed = floor(48 ÷ 4) + 1 = 12 + 1 = 13. Each hoop's semicircular arch length = π × (14 ÷ 2) = π × 7 = 21.99 ft.
Cover area = 21.99 ft × 48 ft = 1,055.6 sq ft of sides-and-roof coverage — the minimum sheet size before adding allowance for ground-burial, seam overlap, and the two end walls this calculator doesn't cover. A larger 96×20 ft commercial-scale house at the same 4 ft spacing needs 25 hoops and 3,015.9 sq ft of cover, showing how cover area scales with both length and width while hoop count tracks length alone.
Questions
How far apart should hoops be spaced?
4 ft on-center is a widely used spacing for typical snow and wind loads on 11- or 12-gauge steel arches, and it's the default this calculator uses — but the actual required spacing depends on your local snow load, hoop material and gauge, and covering type. Commercial NRCS-funded high tunnels and university extension plans often specify spacing in that same range, but check a design appropriate for your climate before building, especially in heavy-snow regions.
Why doesn't the cover area include the end walls?
The formula here computes only the semicircular sides-and-roof surface — arch length times house length — because end-wall shape varies a lot between builds: some are flat vertical walls, others taper to match the hoop curve, and many include a door frame that changes the cutout. Add your end walls' area separately based on your actual end-wall design; this calculator's cover-area figure is a sides+roof subtotal, not a complete bill of material.
Does house width really equal the hoop diameter?
Yes, for the classic semicircular Quonset-style profile this calculator models: each hoop is bent into a half-circle, so the width of the house at the ground equals that semicircle's diameter. Gothic-arch or other non-semicircular hoop profiles have a different, taller relationship between width and arc length, so this formula is specific to true round-top hoop houses, not peaked or gothic-style tunnels.
How much extra cover material should I buy beyond the calculated area?
Plan on meaningfully more than the bare geometric cover area — growers commonly add several feet on every side for securing the plastic in a ground trench or with baseboards, plus overlap where separate sheets join, plus whatever the end walls need. This calculator gives you the sides+roof minimum only; treat it as a starting point for ordering, not the final cut length to request from a supplier.
Can I use this for a gothic-arch hoop house instead of round-top?
Not directly — the semicircular arch-length formula (π × radius) only applies to a true round-top, Quonset-style cross-section. Gothic-arch and peaked-roof hoop houses have straighter side walls and a different roof curve, so their arch length per hoop runs longer relative to width than a plain semicircle. Use a manufacturer's or plan-specific arch-length figure for those styles rather than this formula.