What is the Hoop House Calculator?
A hoop house (also called a high tunnel or polytunnel) is an unheated greenhouse built from a series of semicircular hoops covered with greenhouse plastic. This calculator estimates how much cover material you need by treating each hoop as half a circle and multiplying its arc length by the length of the structure.
How to use it
Enter the hoop width (diameter) — the distance across the base of the arch — and the house length running down the structure. The calculator returns the arc length of one hoop and the total square footage of plastic needed to cover the curved roof from ground to ground.
The formula explained
A semicircle's arc length is half the circumference of a full circle: \(\frac{\pi \times d}{2}\). Because the cover drapes over every point along the length of the house, you multiply that arc length by the house length to get the curved surface area:
$$\text{Cover Area} = \frac{\pi \times d}{2} \times L$$This covers the roof; add extra for end walls, burying the edges, and overlap.
Worked example
For a hoop 12 ft wide on a 20 ft long house: arc length = \(\frac{\pi \times 12}{2} = 18.85\) ft. Cover area = \(18.85 \times 20 = 376.99\) sq ft. Buy a roll at least this wide and long, plus 2–3 ft extra on each dimension for anchoring.
FAQ
Does this include the end walls? No — it only covers the curved roof. Size end-wall plastic separately based on the semicircle area (\(\frac{\pi \times r^2}{2}\)).
How much extra should I add? Add roughly 1–3 ft to both the width and length so you can bury or clamp the edges and allow for overlap.
What units? The tool is unit-agnostic but labeled in feet; if you enter meters, the area will be in square meters.
