Tunnel From the frame

Tunnel Length m

Width at the Ground m

Ridge Height m

Half the width for a round (semicircular) hoop; more for a taller, gothic-looking arch.

Hoop Spacing m

Cover From the fitting method and the roll label

Edge Buried or Battened, Each Side cm

Allowance at Each End m

Cover carried past the end hoops to gather or fix down; zero if the ends are separate panels.

Widest Sheet You Can Buy m

Cover Weight g/m²

From the label or data sheet; film sold by thickness has a weight per m² too.

Cover Sheet Area

— m²

Arch plus buried edges, times the length plus both end allowances

Cover & Frame

Arch Length over the Hoops: — m
Sheet Width Needed: — m
Sheet Width Left over (Negative = Too Narrow): — m
Sheet Length Needed: — m
Both End Walls (If Covered Separately): — m²
Cover Mass: — kg
Floor Area Covered: — m²
Hoops: — hoops

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.**

Polytunnel & Crop Tunnel Cover: Arch Length, Sheet Size, End Walls, Mass & Hoops — free, with the formula and a worked example, at Textile School.