Hoop houses (high tunnels, polytunnels) extend the growing season with a frame of bent hoops covered in greenhouse film. Quonset hoops form a half-circle (height = half the width); gothic hoops are taller and shed snow better. Heat loss is roughly the covering area times its U-value: about 1.15 BTU/(h·ft²·°F) for single poly and 0.7 for inflated double poly.
How to use the Hoop House Calculator
- Width
- Height of arch
- Length
- Straight side-wall height
- Hoop spacing
- Covering
- Minimum inside temperature
- Design outside temperature
- Film price
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the width, height and length of the house, any straight side-wall height, the hoop spacing, the covering type, film price and the temperatures. The calculator approximates the hoop as half an ellipse to find the covering, and estimates the heater size.
Tips for an accurate estimate
- Take measurements at floor level and at the ceiling – walls and rooms are often slightly out of square.
- Use the manufacturer’s coverage, spacing and installation data when it differs from the typical values here.
- Keep a little extra of every finish material for touch-ups and repairs later.
- Check local building codes and permits before structural, electrical, plumbing or gas work.
Common mistakes to avoid
- Sizing heating or cooling equipment by area alone when insulation, windows and climate make a big difference.
- Buying too little paint, stain or flooring and ending up with mismatched batches.
- Overlooking the extra material for steps, railings, gables and trim.
Inputs explained
| Field | What to enter |
|---|---|
| Width | Units: ft, m, in, yd, cm |
| Height of arch | Units: ft, m, in, yd, cm |
| Length | Units: ft, m, in, yd, cm |
| Straight side-wall height | Units: ft, m, in, yd, cm |
| Hoop spacing | Units: ft, m, in, yd, cm |
| Covering | Choose one: Single poly film (U ≈ 1.15), Double poly, inflated (U ≈ 0.70), Twin-wall polycarbonate (U ≈ 0.65), Single glass (U ≈ 1.13) |
| Minimum inside temperature | Units: °F, °C |
| Design outside temperature | Units: °F, °C |
| Film price | Units: /ft², /m², /yd² |
What each result means
- Hoop (arch) length = pi÷2×(3×([Width]÷2 + [Height of arch]) – sqrt((3×[Width]÷2 + [Height of arch])×([Width]÷2 + 3×[Height of arch]))) + 2×[Straight side-wall height]
- End wall area (both) = 2×(pi÷4×[Width]×[Height of arch] + [Width]×[Straight side-wall height])
- Total covering area = [Hoop (arch) length]×[Length] + [End wall area (both)]
- Floor area = [Width]×[Length]
- Hoops = ceil([Length]÷[Hoop spacing] – 0.000001) + 1
- Film cost = [Total covering area]×[Film price]
- Heater capacity = [Total covering area]÷0.09290304×[Covering]×([Minimum inside temperature] – [Design outside temperature])×1.8
Example values
How the main result changes when Width changes and everything else stays at the example values above:
| Width (ft) | Total covering area (ft²) |
|---|---|
| 10 | 1,320 |
| 15 | 1,562 |
| 20 | 1,822 |
| 25 | 2,094 |
| 30 | 2,375 |
| 40 | 2,954 |
Formula
Arch length (half-ellipse) = π/2 × [3(a + b) − √((3a + b)(a + 3b))], a = W/2, b = HCover = arch × L + 2 × end walls (π/4 × W × H) + side wallsHeater (BTU/h) = cover area × U × (T inside − T outside)Worked example
Inputs — Width: 20 ft; Height of arch: 10 ft; Length: 48 ft; Straight side-wall height: 0 ft; Hoop spacing: 4 ft; Covering: Single poly film (U ≈ 1.15); Minimum inside temperature: 40 °F; Design outside temperature: 10 °F; Film price: $0.15 /ft².
Results — Hoop (arch) length = 31.42 ft; End wall area (both) = 314 ft²; Total covering area = 1,822 ft²; Floor area = 960 ft²; Hoops = 13; Film cost = $273.32; Heater capacity = 62,863 BTU/h.
Frequently asked questions
How much plastic do I need for a hoop house?
Buy film about the arch length plus 4–8 ft of overlap for burying or fixing, and the house length plus the end walls if you cover them in film.
Quonset or gothic?
Gothic hoops shed snow better and give more headroom at the sides; Quonset hoops are cheaper and easier to build.
How far apart should hoops be?
4 ft is standard; 6 ft in mild, snow-free areas with strong hoops.
What formula does the Hoop House Calculator use?
Arch length (half-ellipse) = π/2 × [3(a + b) − √((3a + b)(a + 3b))], a = W/2, b = H.