Hoop House Calculator

Plan a hoop house with a materials estimate

A hoop house is a simple covered growing structure made from repeated curved hoops, long purlins, ground supports, and a flexible greenhouse cover. It is also called a high tunnel, garden tunnel, or hoop greenhouse. This hoop house calculator helps estimate the main dimensions and quantities before you buy materials. Enter the building width, length, arch rise, sidewall height, hoop spacing, and cover allowances to see an organized planning list.

The calculator estimates the radius and curved length of a circular arch, number of hoops, actual spacing, purlin length, baseboard length, ground stakes, end-wall area, and greenhouse film size. The curved roof is treated as a circular segment. When the rise is half the width, the arch is a semicircle. A lower rise creates a flatter arc. Vertical sidewalls can be added below the curved section to make more usable growing space near the edges.

A materials calculator is a starting point, not a structural design. Hoop size, pipe material, connectors, anchoring, wind exposure, snow load, soil, and local rules all affect safety and durability. Follow plans from a trusted agricultural extension, engineer, or manufacturer for your region. Confirm every measurement against the actual parts before ordering or cutting materials.

How to use the hoop house calculator

Choose feet or metres, then enter the outside width and length of the structure. Width is the ground-level distance from one side to the other. Length is the long side of the tunnel. Enter arch rise as the vertical distance from the top of the sidewall to the crown of the arch. If the hoops form a semicircle, rise is one-half of the width. Enter zero sidewall height if the curved hoop begins at ground level; otherwise enter the straight wall height beneath the arch.

Set the desired hoop spacing along the length. The calculator rounds the hoop count up so the spacing does not exceed your target and then reports the resulting even spacing. This helps distribute supports evenly from one end frame to the other. Enter the number of longitudinal purlin rows, including the ridge purlin. Purlins connect the hoops along the length and help keep the frame aligned, but the correct number and attachment details depend on the design and loads.

Enter the cover overlap you want at each end and at each side of the cover. The calculator estimates one continuous roof cover dimension plus material for both end walls. Add a waste percentage for trimming, repairs, and handling. Enter end-wall door width and height, and the number of doors, to deduct their opening area from the end-cover estimate. The calculator assumes openings are rectangular and does not calculate door framing or hardware.

Hoop house arch length and radius formula

A circular arch can be described by its chord width and rise. The width is the straight distance between the two spring points where the arch meets the sidewalls. Rise is measured upward from that line to the crown. The calculator finds the radius of the circle that fits those dimensions, then calculates the angle and curved arc length. This is more useful than treating every arch as a half circle because many growing structures use a flatter or taller profile.

For chord width W and rise H, the circular radius R is (W² + 4H²) ÷ (8H). The central angle is 2 × asin(W ÷ 2R), in radians. The curved arc length is R × angle. Total hoop tube length adds two straight sidewall sections to the curved arc. The end-wall curved area uses the circular segment area, R² × (angle − sin(angle)) ÷ 2, plus a rectangle for the vertical sidewalls.

For a semicircle, rise equals half the width, the radius equals half the width, and the curved arch length is π times the radius. For example, a 20-foot-wide half-circle has a 10-foot radius and an arch length of about 31.4 feet before adding sidewalls, connection allowance, or burial depth. Real tube length can differ because of bend radius, fittings, embedment, and the manufacturer's forming method.

• Arch radius = (width² + 4 × rise²) ÷ (8 × rise)
• Arch angle = 2 × asin(width ÷ (2 × radius))
• Curved arch length = radius × arch angle
• Hoop stock length = curved arch length + 2 × sidewall height
• Hoop count = ceiling(house length ÷ target spacing) + 1
• Even hoop spacing = house length ÷ (hoop count − 1)

Hoop spacing and frame material estimates

Hoop spacing is the distance between adjacent frames along the tunnel. The entered spacing is a maximum target: the count is rounded up and the structure is divided into equal bays. For example, a 48-foot tunnel with a target of 4 feet gives 13 hoops and 12 equal spaces, so the actual spacing is 4 feet. If a length does not divide evenly, the calculated spacing becomes a little smaller than the target rather than leaving a short final bay.

Purlins run lengthwise and connect multiple hoops. The simple material estimate multiplies the number of purlin rows by the house length. It also estimates two side baseboards by multiplying length by two. These are linear footage totals; they do not account for splice overlaps, joints, end framing, bracing, ridge boards, cross ties, or stock lengths. Add those items from your chosen plan and allow for usable cut lengths when buying lumber or pipe.

Ground stakes are estimated as two per hoop, one on each side. Some designs use driven pipe, ground posts, plates, concrete footings, or different anchors. Do not assume this stake count or embedment is adequate for your soil or weather. A high tunnel exposed to strong wind or heavy snow needs a frame and anchoring system designed for those forces. Use the manufacturer's spacing and foundation instructions.

Greenhouse plastic and cover size

A single-piece roof cover needs enough width to travel from one ground edge, over one sidewall and the arch, across the crown, down the other sidewall, and reach the attachment point. In this estimate, the base cover width is the hoop length plus the selected side overlap on both sides. The cover length follows the tunnel length with end overlap added at each end. The calculator adds the waste percentage to these dimensions and reports both the required roll dimensions and approximate area.

End walls are estimated separately as two curved faces. Each face includes the rectangle below the arch and the circular segment above it. Door opening area is subtracted for the entered number of doors, then the waste allowance is applied. This gives an approximate film area for the ends. If the ends use rigid polycarbonate, plywood, lumber, or another material, use this area as a rough surface estimate and make a separate takeoff for framing and cladding.

Greenhouse films are sold in specific widths, thicknesses, and roll lengths. Confirm the usable width, UV treatment, warranty, attachment system, and recommended installation tension with the supplier. Real cover sizing may need extra film for wiggle wire channels, baseboards, buried edges, end folds, doors, and future repairs. Never order based only on the calculated square area if the required roll width is unavailable.

Worked example for a garden hoop house

Suppose you plan a 20-foot-wide and 48-foot-long tunnel with a 10-foot rise, no straight sidewall, and hoops no farther apart than 4 feet. A 10-foot rise across a 20-foot chord makes a semicircle. The calculated radius is 10 feet and the arch length is about 31.4 feet. That is the curved portion of each hoop before any attachment, ground insertion, or cutting allowance.

At 4-foot target spacing, the structure uses 13 hoop frames and has 12 equal bays at 4 feet each. If you choose five purlin rows, the simple purlin total is 5 × 48 = 240 linear feet. The two side baseboards add 96 linear feet. Two stakes per hoop give a basic estimate of 26 ground supports. The end-wall shape area is about 157 square feet for both ends together before subtracting doors and applying waste.

For a roof cover with 1 foot of side overlap on each side and 2 feet of end overlap at each end, the base dimensions are roughly 33.4 feet wide by 52 feet long. Add any waste allowance and compare the resulting width with actual film roll sizes. This example is only a geometry and quantity illustration. Frame spacing and anchoring must be selected for the structure, local wind and snow conditions, soil, materials, and instructions.

Choosing hoop house dimensions for growing

Width affects the arch profile, interior span, and the amount of cover needed. A wider tunnel can provide more growing rows, but it also needs a longer arch and a frame designed to carry the wider span. Length adds growing area and can be extended by adding bays, but it also increases the number of hoops, purlin footage, baseboard footage, and plastic length. Consider how the structure fits the site, access paths, irrigation, and crop workflow before choosing dimensions.

Sidewall height affects headroom and usable bench or bed space near the edges. Taller straight sidewalls can make work easier and improve ventilation options, though they change wind exposure and frame forces. Arch rise controls how tall and rounded the roof is. A flatter arch uses less height but may shed snow differently from a steeper arch. The tool computes geometry; it does not judge whether a shape is appropriate for the climate or covering material.

Plan doors, vents, and end walls early. Door locations affect crop movement, wheelbarrow access, and end-frame bracing. Ventilation openings may be essential for temperature and humidity management. The calculator subtracts only simple rectangular door area from the plastic estimate; it does not design ventilation, door swing, framing, or structural reinforcement. Follow local growing recommendations and supplier guidance.

Purlins, baseboards, end walls, and fasteners

Purlin rows commonly include a ridge line and additional lines down the shoulders or sides. The right layout depends on hoop material, span, attachment hardware, covering, and expected loads. Enter a row count that matches the plan you intend to build. The calculator reports total linear length but does not decide purlin spacing around the arch or identify the correct size, grade, connector, or fastener.

Baseboards can secure the cover along the long sides and may also act as a low wall or attachment surface. End walls often need posts, a door frame, diagonal bracing, and additional blocking. These parts can use substantial material that a simple area estimate cannot capture. Build a cut list from a drawing and account for saw cuts, overlap, joints, defects, and standard lumber lengths.

Cover attachment methods include channels, wiggle wire, battens, ropes, and other systems. Each has its own fasteners and installation details. Some designs use a second layer of film with inflation, while others use a single layer. If using two layers, the required cover quantity may be different from a single cover. Follow the product guide for film tension and attachment so the cover does not tear or loosen in wind.

Site, weather, and safety considerations

Choose a level, well-drained location with access to water, power if needed, and a route for materials. Avoid low spots where runoff collects and consider prevailing winds, shade, nearby trees, and snow drifting. Orienting a tunnel for light and ventilation is a site-specific choice. Check property boundaries, easements, utility lines, permits, and agricultural structure rules before digging or building.

Wind and snow can place heavy forces on a hoop structure. Soil type changes how anchors hold, and wet or frozen ground can affect installation. Plastic can act like a sail when the frame is exposed. A hoop count, stake number, or tube length from a calculator is not a safety rating. Use engineered or regionally tested plans where required, and do not modify a rated structure without checking with its manufacturer or a qualified designer.

Wear appropriate eye, hand, and hearing protection when cutting or bending materials. Secure long pipe before cutting, keep bystanders clear of springing hoops, and use ladders safely when attaching film. Follow the instructions for tools, adhesives, coatings, and treated lumber. If a project involves electrical equipment, heaters, or irrigation controls, follow relevant codes and hire a licensed professional where required.

Common estimating mistakes

One common mistake is treating the target hoop spacing as an exact bay count without checking the end frames. This calculator rounds the count upward and redistributes the length into even spaces. Another is measuring the ground width but using an arch rise that belongs to a different profile. Check that width and rise describe the same chord and spring points. Add sidewall height separately rather than including it in the rise.

Cover area and cover dimensions are not interchangeable. A roll may have enough square footage but still be too narrow to cross the arch. Check the needed width and length against the available roll. Include the material needed to attach, fold, bury, or wrap the film. Similarly, total purlin footage may not match stock lengths after overlaps and splices, so turn the quantity into a practical cut plan before ordering.

Finally, remember that the calculator cannot know what is included in your kit. Some kits supply hoops, ground posts, purlins, clips, or film; others provide only a frame. Compare this estimate with the supplier bill of materials and remove duplicates. Treat the calculated list as a checklist for discussion, then use the plans and product instructions as the final source for assembly details.

Limitations of this hoop house estimate

This calculator models a circular arch, straight sidewalls, even hoop spacing, basic longitudinal members, and approximate sheet coverage. It does not model Gothic bows, peaked roofs, asymmetric profiles, slope, uneven ground, special end frames, buried tube length, connector geometry, structural deflection, snow or wind load, or a particular manufacturer's kit. Its end-wall area is geometric and does not replace a framing plan.

Use dimensions from the same reference points and select the correct measurement units. If the structure uses several widths, sidewall heights, or arch shapes, calculate each section separately and combine the quantities carefully. The output is a planning aid for materials and dimensions, not an engineering design, construction permit, or guarantee that a structure is safe for a site.

Confirm local requirements and consult an agricultural extension service, greenhouse supplier, engineer, or qualified builder where appropriate. For growing recommendations, use local horticulture guidance. Safe construction depends on the complete design, workmanship, materials, anchoring, and maintenance.