Polytunnel & Crop Tunnel Cover: Arch Length, Sheet Size, End Walls, Mass & Hoops

The formula

This is the expression the tool evaluates. Every term is named underneath, with the unit it must be supplied in.

How the result is derived

Step by step, from the values you type to the figure on screen.

1. The 8 inputs are read from the form on every keystroke: Tunnel Length, Width at the Ground, Ridge Height, Hoop Spacing, Edge Buried or Battened, Each Side, Allowance at Each End, Widest Sheet You Can Buy and Cover Weight.
2. Each value is checked against the accepted range in the input table below. A value outside its range stops the calculation rather than producing a misleading figure — the results blank out and a message appears.
3. The validated values are substituted into the expression above, which resolves Cover Sheet Area together with every supporting figure in one pass — no value is carried over from a previous entry.
4. The supporting outputs — Arch Length over the Hoops, Sheet Width Needed, Sheet Width Left over (Negative = Too Narrow), Sheet Length Needed, Both End Walls (If Covered Separately), Cover Mass, Floor Area Covered and Hoops — come from the same pass, so they always describe the same case as the headline figure.
5. Results are rounded for display only. The full-precision value is used throughout the chain, so reading a rounded intermediate figure back into the tool by hand can shift the last digit.

What each input means

Where to read each value on the floor, the unit it must be in, and the range the tool accepts.

What the tool returns

The headline figure and every supporting value it is built from.

Worked example

Substituting

The floor is 165 m². The cover is twice that, before the ends.

How to use it

1. Work through the input groups in order — Tunnel and Cover. The defaults are a realistic case, so you can change one value at a time and watch what moves.
2. There is no calculate button. Every figure recalculates as you type or drag, which is what makes this usable for a what-if sweep rather than a single answer.
3. Read Cover Sheet Area in the dark results panel — that is the headline figure, expressed in m².
4. Check the supporting rows underneath (Arch Length over the Hoops, Sheet Width Needed, Sheet Width Left over (Negative = Too Narrow), Sheet Length Needed, Both End Walls (If Covered Separately), Cover Mass, Floor Area Covered and Hoops) before acting on the headline — they are where an implausible input usually shows itself first.
5. Reset to defaults returns every field to the reference case, which is the quickest way to check whether a surprising result came from the tool or from an input you had changed earlier.

Where this is used

• Process planning — establishing Cover Sheet Area before a trial is booked, so machine time and material in Agrotextiles & Environmental Shielding are committed against a calculated figure rather than an estimate.
• Costing and quotation — Cover Sheet Area is an input to the cost sheet, and quoting from a worked number rather than a remembered one is what keeps a margin intact.
• Troubleshooting — when the floor result drifts from plan, entering the measured values (starting with Tunnel Length) shows how much of the gap in Cover Sheet Area each variable explains.
• Teaching and study — the accepted ranges bracket normal Agrotextiles & Environmental Shielding practice, so moving one variable at a time shows the shape of the relationship rather than a single answer.

Reading the result

Typical bands and what each one is telling you.

Assumptions and limits

• The arch is taken as half an ellipse standing on the ground: half the width across and the ridge height up, which is a semicircle when the height is half the width. Straight-walled tunnels and gothic arches differ, so measure one hoop with a tape if the frame is not round. Edges, end allowances and the sheet sizes on sale are yours. End walls are counted as half-ellipses for doors or panels cut separately; an end gathered from the main sheet is in the end allowance instead. Cover mass is the main sheet only. **This is a cover take-off; it does not check the frame or the anchoring against wind.**
• Every input is bounded to the range normal practice occupies (Tunnel Length 1 to 500 m, Width at the Ground 0.5 to 30 m and Ridge Height 0.3 to 10 m, and so on for the rest). Those bounds are guard rails against typing errors, not a claim that the formula fails one unit outside them.
• The calculation is deterministic: the same inputs always give the same result. It carries no allowance for machine condition, operator skill, ambient conditions or lot-to-lot material variation unless an input above explicitly represents one.
• Nothing is sent anywhere. The maths runs in your browser, so the numbers you type never leave the page.

Standards and further reading

• The cover maker's data: weight per square metre or thickness, light or shade figures, mesh for insect nets, and UV life.
• The tunnel frame maker's instructions for hoop spacing, anchoring and how the cover is fixed.

Questions people ask