How much row cover fabric do I need for a raised bed hoop tunnel? Generic hoop-house tools skip the bed-scale answer: the fabric must go over the hoop arc, down both sides for anchoring, and past both ends. This page does that whole cut — arc, anchor allowances, end allowances, hoop count and roll cuts — for one bed size at a time, repeated for as many beds as you enter. It runs entirely in your browser and saves or sends nothing. All lengths are in feet.
The hoop is treated as a circular arc over the bed width. Radius R = (width² + 4 × height²) ÷ (8 × height). Arc length = R × 4 × atan(2 × height ÷ width). Cut width = arc + 2 × anchor allowance. Cut length = bed length + 2 × end allowance. Hoops per bed = ceil(bed length ÷ hoop spacing) + 1, so there is a hoop at both ends. Cuts per roll = floor(roll length ÷ cut length). Rolls needed = ceil(beds ÷ cuts per roll), counting one cut per bed.
With the defaults above: bed 10 ft long and 4 ft wide, hoop height 1.5 ft. Radius = (16 + 9) ÷ 12 = 2.08 ft. Arc = 2.08 × 4 × atan(0.75) = 5.36 ft. Cut width = 5.36 + 2 × 1 = 7.36 ft. Cut length = 10 + 2 × 1 = 12.00 ft, so one cut covers 88.35 sq ft. Hoops per bed = ceil(10 ÷ 3) + 1 = 5, or 10 for 2 beds. A 50 ft roll gives floor(50 ÷ 12) = 4 cuts, so 2 beds need 24.00 ft of fabric in total and 1 roll.
What if the cut width is wider than the roll? The page will warn you: a single cut cannot come out of that roll width, so you need a wider roll or a joined seam, and a seam changes how the cover handles wind and water. Why must hoop height stay below half the bed width? This arc model is for a low, shallow tunnel; a taller hoop over the same width is a different shape and the formula no longer describes it. Does this cover wind or frost protection? No. It only sizes the cut and counts hoops and rolls. Fabric weight, frost rating, anchoring in wind and whether a crop needs venting are separate checks against the fabric and crop guidance you use. Is this a buying recommendation? No. It only counts fabric and hoops; you check fabric type, price and availability yourself. This page is not professional gardening or structural advice.
This is a free, single-purpose calculator. All calculation happens in your browser. No account, no upload, no tracking by this page beyond any ads Google may serve after approval.