Windsock Size Requirements
A bigger windsock is not always better, but the right size for your application absolutely matters. For regulated sites, minimum dimensions are specified in standards that your installation must meet. For unregulated sites, the correct size is determined by the viewing distance and the wind speed range you need to indicate.
Aviation: the ICAO Annex 14 specification
For licensed aerodromes, the minimum size requirement is set by ICAO Annex 14 and referenced in CAA CAP 168. The wind direction indicator must be a truncated cone at least 3.6 metres (12ft) in length with a mouth diameter of at least 0.9 metres (36 inches). This is why 12ft is the universal aerodrome standard.
The size is set to ensure the sock is visible from aircraft at circuit height and from the runway threshold, not because 12ft is inherently superior to 8ft. At smaller aerodromes or unlicensed private strips, a smaller sock may be used, but 12ft remains the recognised best-practice specification for any site where aircraft are operating.
For offshore helidecks, size is specified per installation under CAA CAP 437 rather than as a universal minimum.
Recommended size by application
The right size for your site depends on the primary viewing distance: how far away is the person or aircraft that needs to read the sock?
Licensed aerodromes: 12ft. ICAO Annex 14 minimum, referenced by CAP 168. This is not negotiable for a licensed site.
Private airstrips and gliding sites: 8ft to 12ft. 12ft is best practice; 8ft is acceptable on smaller sites with shorter circuit distances.
Onshore helipads and heliports: 4ft to 8ft, depending on the approach path distance and surrounding structure height.
Chemical, EfW and other COMAH industrial sites: 4ft to 6ft on a 3m to 5m mast, visible from all muster points.
Ports and marine construction: 6ft to 8ft to be readable from crane cabs and vessel wheelhouses across a large operational area.
Water treatment and waste sites: 4ft to 6ft, visible from the primary muster point and chemical storage areas.
Farms, golf courses and events: 3ft to 4ft is typically sufficient for short-range direction indication.
For a full breakdown with pole height guidance, see our size guide.
Mouth diameter and hardware compatibility
The mouth diameter determines which swivel arm your sock fits. A 15-inch mouth sock fits a shorter swivel arm; a 36-inch mouth sock requires a longer arm to prevent the tail wrapping the mast. When ordering a replacement sock, specify the size rather than just the length to ensure hardware compatibility. Our team can advise on swivel arm matching if you are unsure of your current installation.
Browse our full windsock range in sizes from 3ft to 12ft, or contact us for sizes outside the standard range.
FAQ's
What size windsock does an aerodrome need?
ICAO Annex 14, referenced by CAA CAP 168, requires a minimum length of 3.6 metres (12ft) with a mouth diameter of at least 0.9 metres (36 inches) for licensed aerodromes. 12ft is the standard specification worldwide.
What size windsock do I need for a helipad?
4ft to 8ft for most onshore helipads, sized to be clearly readable from the approach path. Offshore helidecks are specified per installation under CAP 437. See our heliports page for the full specification.
Does sock length affect wind response?
No. Wind response is determined by fabric weight and coating, not length. A larger sock requires more wind energy to extend simply because of its greater mass, but a correctly specified fabric in any size will meet the 3-knot to 15-knot performance requirement.
Can I use a smaller sock on an aerodrome to save money?
Not on a licensed aerodrome where CAP 168 applies. The 12ft minimum is a licensing requirement and will be checked at inspection. On unlicensed sites, smaller socks are acceptable, though 12ft remains best practice wherever aircraft are operating.