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Raised Bed Hoop & Fabric Fit
PVC hoop count, pipe length and row-cover fabric for a raised bed high tunnel.
Raised Bed Hoop & Fabric Fit
Chlorova · updated for 2026
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Click “Calculate” to see your results.
Hoop arc is measured along the curve, not over the top, which is what actually matters for pipe length; the fabric figure adds two feet of tuck on every side. Wind and snow loads change both numbers — a tight winter tunnel wants fewer inches of sag and more hoops than the summer insect-cover default this tool assumes.
The raised bed hoop calculator sizes a low tunnel or high tunnel in a single shot: how many PVC hoops to cut, how many ten-foot pipes that requires, and how much row cover or greenhouse plastic to buy to fit the resulting arch. It reads the arc length along the curve rather than over the top — which is the number home builders always get short — and it pads the fabric by tuck margin on every side. Enter your finished bed dimensions and hoop spacing, and it returns the exact shopping list for a season of season-extending cover.
How to Use the Hoop Calculator
- Enter the outside width of the raised bed in inches.
- Enter the length of the bed in feet, corner to corner.
- Set hoop spacing along the bed — 24 inches is a good all-purpose default.
- Set the pipe stock length; ten-foot sections are the hardware-store standard.
- Read the arc length so you know how high each hoop will stand.
- Count the hoops, the pipe sticks to buy and the fabric square footage.
- Add one or two spare hoops because a first-attempt pipe bend is rarely round.
The Hoop-Arc and Fabric Math, Explained
Each hoop is a half-circle whose arc length is π × r, so arc_ft = 3.1416 × (bed_width_in ÷ 2) ÷ 12. That curve, not the flat top, is the pipe you actually cut. The hoop count runs from the bed's length divided by the spacing plus one extra, so a 96-inch run at 24-inch spacing gets five hoops rather than four. Multiply out for linear feet of pipe, which divides by the stock length and rounds up to whole sticks. Fabric area is the arc plus a two-foot tuck on each side, times the bed length plus the same two-foot front and back allowance.
Why the curve matters more than height: a 48-inch bed's arc is roughly 6.28 ft — a 10-foot stick makes exactly one hoop with a small off-cut, and two sticks join cleanly with a short connector sleeve for a taller arch. Skipping the extra hoop at the closed end of a run is the number-one mistake; that open end is where flapping fabric wears out first and where most winter heat loss escapes.
Worked Example: Standard 4 × 8 Bed
- Bed width 48 in, bed length 8 ft, hoops every 24 in, 10-ft pipe stock.
- Arc per hoop: 3.1416 × 48 ÷ 2 ÷ 12 = 6.28 ft.
- Hoop count: floor(8 × 12 ÷ 24) + 1 = 4 + 1 = 5 hoops.
- Total pipe: 5 × 6.28 = 31.4 ft, so ceil(31.4 ÷ 10) = 4 sticks at the hardware store.
- Fabric: (6.28 + 2) × (8 + 2) = 82.8 sq ft — round up to a 3 × 6 yard row cover.
- A single 10-ft stick makes one hoop with a 3.7 ft off-cut, so leftovers naturally become door-frame sides.
- Tuck the two extra feet of fabric on each side under the bed boards or a row of bricks.
- Cut one spare hoop; first-attempt pipe bends are almost never round.
Hoop Height and Arc by Bed Width
Arc and standing height for the common raised-bed widths. Standing height is roughly half the arc, and it is what determines whether you can work under the cover with gloves on without pressing the fabric down onto the plants.
| Bed width | Arc length | Standing height |
|---|---|---|
| 36 in | 4.71 ft | 18 in |
| 48 in | 6.28 ft | 24 in |
| 60 in | 7.85 ft | 30 in |
| 72 in | 9.42 ft | 36 in |
Key Terms
- Hoop
- A single curved piece of pipe spanning the bed width to hold row cover or plastic off the plants.
- Arc length
- The distance measured along the curve of a hoop — the actual pipe length you need to cut.
- Low tunnel
- A short arched cover over a bed that protects without enclosing a walkable space.
- High tunnel
- A taller hoop frame you can work under, usually with side walls and a door.
- Row cover
- A lightweight spun fabric that slides over hoops to exclude insects and add a few degrees of warmth.
- Tuck margin
- Extra fabric on every side, pinned under boards, that stops wind lifting the cover off.
What This Means Before You Buy Pipe
- Use schedule-10 electrical conduit or dedicated greenhouse pipe, not plumbing PVC schedule-40 — it is far stiffer per pound and holds a round arch without bending back.
- For beds you will cover with clear plastic in cold climates, tighter spacing beats taller hoops: 24 inches of arc on a 12-inch snow load holds, 36 inches of arc sags and pools.
- Buy one spare hoop per tunnel and one spare stick per five you cut, because the first pipe you bend always ends up a lazy ellipse rather than a half-circle.
- The fabric square footage is bigger than the bed footprint for a reason — the tuck is what keeps the cover on through a March night and is the single biggest reason these DIY tunnels fail early.
- For a taller arch, join two sticks with a short connector sleeve on top of the hoop rather than bending a longer pipe; a joint at the apex is invisible and structurally sound.
Common Mistakes & Fixes
- Sizing the pipe by the flat top height instead of the curved arc, so the hoop is short and pops off the ends.
- Skipping the extra hoop at the closed end of the run, which leaves fabric flapping and the whole cover working loose by mid-winter.
- Cutting fabric at exactly the bed dimensions with no tuck, so a spring gust lifts it and the tunnel is open by morning.
- Assuming ten-foot pipe makes two hoops on a 4-foot bed — the arc alone is over six feet per hoop, so a stick yields one plus off-cuts.
- Using a single ½-in pipe for a wide bed, which bows under rain and presses the cover onto the plants it was meant to keep clear.
When to Use This (and When Not To)
Use it whenever you are about to build a hoop frame on a finished raised bed — spring insect cover, summer shade-cloth, or winter low-tunnel plastic — and want the shopping list before you make a hardware-store run. It sizes the hoops, the pipe and the fabric for a single span; for a walk-in greenhouse, a quonset hut or a permanent structure, engineering requirements and wind loads go well past what a DIY calculator can responsibly cover. For open-ground beds, use the row-cover fabric number directly, but tack the ends with ground staples rather than the tuck margin the tool assumes.
Raised Bed Hoop & Fabric Fit: Frequently Asked Questions
How tall will a raised bed hoop stand?
Roughly half the arc length, which for a 48-inch-wide bed is 24 inches. That is enough to cover lettuce and brassicas without touching the fabric. Taller arches need joined pipes; a single ten-foot stick tops out near that 24-inch height on a standard bed.
How many PVC hoops per bed do I need?
Divide the bed length in inches by the hoop spacing, round down, then add one for the closed end. A 4 × 8 bed at 24-inch spacing gets five hoops, and a longer 5 × 12 at 36-inch spacing gets five as well. Skipping that extra end hoop is what turns a well-built tunnel into a drafty one.
What kind of pipe should I use for hoops?
Schedule-10 electrical conduit or purpose-made greenhouse pipe bends clean and holds an arch, whereas plumbing PVC schedule-40 is heavier, wants a heat bend and springs back on you. Rebar and copper are overkill; polyethylene water line works in a pinch but kinks.
How much row cover fabric do I buy?
Add the arc length plus a two-foot tuck on each side, then multiply by the bed length with the same two-foot front-and-back allowance. Fabric sold by the linear yard usually works out cheaper than the pre-cut kits, and one extra foot of tuck is far better than one short of what you need.
Can this calculator handle a wide tunnel?
Up to about 72 inches of span on one stick; past that you want a two-piece hoop joined at the apex or a proper frame. Wider spans with taller profiles are structural decisions a small calculator should not pretend to design, so bring the arc numbers to a supplier instead.
Should I space hoops by arc, height or bed length?
Space by bed length and expected load, not arc. Twenty-four inches is a safe all-purpose default, sixteen inches for snow-load winter tunnels, and thirty-six inches is usually the outer edge before fabric starts sagging between supports. The arc sets pipe length per hoop; spacing sets hoop count per bed.
Sources & Further Reading
- Building Hoop Frames and Low Tunnels for Home Gardens — Cornell University Small Farms Program
- High Tunnel Design, Materials and Sizing — Penn State Extension
- Season Extension with Row Cover and Hoops — University of Massachusetts Vegetable Farming Training Program
Chlorova Gardening Team
Builds, checks and documents every tool we publish
Chlorova editorial review
Checked against extension-service publications
Formula verified against published references · Updated
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