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Are you looking at replacing your polythene? Be it diffused or clear, we’ve got the best polythene around. But do you know how much you need?

Our handy guide below is here to help

Polythene calculator illustration

Calculating your sheet width:

First you need to know the width of your polytunnel.
If you own a Northern Polytunnels structure, jump to the next section.
If you’re not sure of the width or height, you should measure the circumference of the polytunnel (A) and then make the following allowances:

Fixing methodAdd per side (approx.
Trenching into the ground1m (3ft) 
Fixing to a base rail0.5m (1’6”)
Fixing to a side rai0.5m (1’6”)

Now you have the width of the polythene you need.

Calculating your sheet length:

Once you’ve measured the length of your tunnel (B) you need to make an allowance for the ends, especially if your cover is fixed to the door frames rather than clipped on to the end hoops.

The width of the structure (C) and the width of the doors are the main considerations. As a general rule when fixing to the door frames you should add 2m (6ft 6in) per end, so for a 6.1m (20ft) tunnel you would order a 10m (33ft) long polythene sheet.

For a 14ft (4.27m) wide polytunnel with single doors at both ends, you would be wise to add another extra metre to be safe.

Use the below table for guidance:

Width of tunnelTrenchedBase RailSide Rail
8ft (2.44m)9.2m7.3m7.3m
10ft (3.05m)9.2m7.3m7.3m
12ft (3.66m)9.2m9.2m7.3m
14ft (4.27m)9.2m9.2m7.3m
16ft (4.9m)9.2m9.2m7.3m

Now you have the size you require, you can order your polythene here