Work out hoops, frame pipe, greenhouse film and cost for a high tunnel. Enter the size, spacing and roll coverage to get rolls, pipe length and total cost.
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A hoop house is a kit of parts: pipe, purlins, ground posts, film, and end walls. Get the hoop count wrong and the frame won’t stand straight. Get the film wrong and you’re one roll short before the season starts. This hoop house calculator works out both from the width, length, and hoop spacing, plus the roof arc, pipe lengths, film area, and a full cost breakdown.
Six preset sizes cover the common backyard and small-farm tunnels, from 10×20 up to 30×72. Custom sizes work too. The tool calculates the roof arc from the width and the rise, then derives the hoop pipe length, the number of hoops, purlin runs, ground posts, and the film area net of doors. Enter local prices and it returns a per-square-foot floor cost alongside the total. Metric and imperial units switch cleanly, converting every entered value.
Pick the unit system: imperial (ft / ft²) or metric (m / m²).
Choose a preset size or set Custom to enter your own dimensions.
Enter the width (span), length, side wall height, and peak height.
Confirm the hoop spacing. Four feet is the common default.
Set the number of purlin runs along the roof.
Enter the ground post length. Two feet is typical for field tunnels.
Set film coverage per roll and the overlap/waste factor.
Add door count, door size, and all your unit prices.
The Summary tab leads with film area and hoops. Detailed Breakdown lists every dimension, quantity, and cost line.
The math starts with the roof arc. A hoop house roof is a circular segment, and the calculator finds its radius, central angle, and arc length from the width and the rise.
Formula: Rise (r) = Peak height − Side wall height
Formula: Arc radius = (Width² ÷ 4 + r²) ÷ (2r)
Formula: Central angle = 2 × arcsin(Width ÷ (2 × Radius))
Formula: Arc length = Radius × Central angle
Formula: Segment area = (Radius² ÷ 2) × (Central angle − sin(Central angle))
Formula: Hoop pipe length = 2 × Side height + Arc length
Formula: Bays = round(Length ÷ Hoop spacing)
Formula: Hoops = Bays + 1
Formula: Total hoop pipe = Hoops × Hoop pipe length
Formula: Total purlin length = Purlin runs × Length
Formula: Ground posts = 2 × Hoops
Formula: End wall area = Width × Side height + Segment area
Formula: Roof film area = Hoop pipe length × Length
Formula: Film (net) = Roof film + 2 × End walls − Door area
Formula: Film with waste = Film (net) × (1 + Waste %)
Formula: Rolls needed = ⌈ Film with waste ÷ Coverage per roll ⌉
Ground posts count is two per hoop because each hoop has two legs. Purlin length runs the full tunnel length for each horizontal run, usually three to five runs depending on hoop spacing. End wall area is the rectangular side wall plus the circular segment above it.
Film area starts from the arc length plus the two side walls, multiplied by the tunnel length. That’s the roof and side wall skin. Then two end walls get added and door openings get subtracted. Waste covers overlap at the seams and trim at the ends. Twelve percent is a safe default.
Baseboard is the two long side walls, so 2 × Length. The cost per square foot of floor area uses W × L, since growers compare tunnels by ground footprint.
Validation is minimal. Peak height must exceed side wall height, or the tool can’t compute the arc.
Say you’re building a 16 ft by 36 ft tunnel with a 4 ft side wall and a 12 ft peak. Hoop spacing is 4 ft, five purlin runs, 2 ft ground posts. Film covers 2,150 ft² per roll, waste is 12%. Two doors, 3 ft wide and 7 ft tall. Costs: $2.50 per foot of hoop pipe, $1.80 per foot of purlin, $18 per ground post, $180 per film roll, $95 per door, $0.80 per foot of baseboard, $600 labor.
Rise: 12 − 4 = 8.00 ft
Arc radius: (16² ÷ 4 + 8²) ÷ (2 × 8) = (64 + 64) ÷ 16 = 8.00 ft
Central angle: 2 × arcsin(16 ÷ (2 × 8)) = 2 × arcsin(1) = π = 180°
Arc length: 8 × π = 25.13 ft
Hoop pipe length: 2 × 4 + 25.13 = 33.13 ft
Bays: round(36 ÷ 4) = 9 bays
Hoops: 9 + 1 = 10 hoops
Actual spacing: 36 ÷ 9 = 4.00 ft
Total hoop pipe: 10 × 33.13 = 331.3 ft
Total purlin: 5 × 36 = 180.0 ft
Ground posts: 2 × 10 = 20 posts, total 40.0 ft
End wall area: 16 × 4 + (8² ÷ 2) × (π − sin(π)) = 64 + 32 × π = 64 + 100.5 = 164.5 ft²
Roof film area: 33.13 × 36 = 1,192.7 ft²
Total film gross: 1,192.7 + 2 × 164.5 = 1,521.7 ft²
Door area: 2 × 3 × 7 = 42 ft²
Film net: 1,521.7 − 42 = 1,479.7 ft²
With 12% waste: 1,479.7 × 1.12 = 1,657.2 ft²
Rolls: ⌈1,657.2 ÷ 2,150⌉ = 1 roll
Baseboard: 2 × 36 = 72 ft
Hoop pipe cost: 331.3 × $2.50 = $828.25
Purlin cost: 180 × $1.80 = $324.00
Ground post cost: 20 × $18 = $360.00
Film cost: 1 × $180 = $180.00
Door cost: 2 × $95 = $190.00
Baseboard cost: 72 × $0.80 = $57.60
Material subtotal: $1,939.85
Labor: $600.00
Total: $2,539.85
Cost per ft² of floor: $2,539.85 ÷ (16 × 36) = $4.41
Ten hoops on a 16×36 tunnel with 4 ft spacing. One roll of film covers it, since a standard 2,150 ft² roll leaves margin. The pipe frame is the biggest material line at this size, which is typical for a tunnel with 5 purlins.
Divide length by hoop spacing, round to the nearest whole number, then add one. A 36 ft tunnel at 4 ft spacing has 9 bays and 10 hoops. The extra hoop is the end wall.
The arc depends on width and rise. A 16 ft wide tunnel with an 8 ft rise has an arc of about 25 ft. The calculator derives this from the circular segment geometry.
Add roof film (arc plus side walls, times length) to two end walls, subtract door area, then add waste. A 16×36 tunnel needs about 1,480 ft² net and 1,657 ft² with 12% waste.
Twelve percent is standard. Long tunnels with multiple panels can run 15 percent. Short single-panel tunnels can drop to 8 percent.
Three to five runs. Three for a small tunnel in a mild climate. Five for larger tunnels or those in snow and wind zones. The calculator defaults to five.
Two feet for a field tunnel with driven posts. Three to four feet for permanent structures on footings. Post diameter matches the hoop pipe, usually 1-5/8″ or 1-7/8″.
Depends on what you grow and how you work inside. A 12×24 tunnel handles a small garden or starter farm. 16×36 is a common middle size. 30×72 suits commercial production.
Baseboards anchor the film along each side wall and add rigidity. Some tunnels use a film-lock channel instead. Either way, baseboard length equals twice the tunnel length.
Hoop houses are unheated or minimally heated tunnels with a plastic film cover. Greenhouses are permanent structures with glass or rigid panels and often full climate control.
Yes. High tunnel is the USDA term for a hoop house. The math is the same, and the calculator handles any size from a small backyard tunnel to a commercial high tunnel.
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