Hoop House Calculator

Use this hoop house calculator to find the surface area and the heater size for your greenhouse.

Hoop length18 ft 10.19 in18.85 ft of pipe per hoop

Hoops needed76 bays at 4 ft, plus one

Total pipe131.95 fthoops only, before purlins

Peak height6 fthalf the width, for a semicircle

Covering size22.8 × 32 ftwith 2 ft each side and 4 ft each end to fasten

Covering area731.2 sq ft

Growing area288 sq ft26.756 m²

Enclosed volume1,357.2 cu ft38.43 m³

Ridge purlin24 ftone along the peak; two more each side is usual

Ground posts14two per hoop

Ventilation needed57.6 sq ftroll-up sides of about a fifth of the floor area

Spacing in snow country4 ftclose the hoops to 4 ft or less where snow loads are real, and brace the end walls

The formula

hoop length = semicircular arc = π × width ÷ 2

Half a circumference

A semicircular hoop over a span w is half the circumference of a circle of diameter w, so the pipe length is π w ÷ 2 — about 18 feet 10 inches for a 12-foot house. Adding straight sidewalls raises the peak and adds twice the sidewall height to each hoop.

Order the covering generously. You need a couple of feet each side to bury in a trench or clamp to a base rail, and about four feet at each end to wrap the end walls. Running short here is much more annoying than running long.

Hoop spacing is a snow-load decision more than a material one. Four feet is standard; where snow accumulates, close it up and brace the ends, because a collapsing hoop house nearly always goes at the gable.