Beaufort Scale of Wind Force

Sometimes people or manufacturers use the Gale Force description to describe the performance potential of products or fabrics in extreme conditions.

Here's a brief breakdown of the scale and the associated wind strength associated with it (with some amendments for campers!) 
Scale Force Rating Observable Land Effects Speed MPH
0 Calm Vertical Smoke (Tent flysheet remains still.) 1
1 Light Air Slight smoke drift (Tent flysheet remains mostly still, with occasional ripples.) 1-3
2 Light Breeze Leaves gently rustle (Gentle flapping of flysheet and unsecured tent flaps.) 4-7
3 Gentle Breeze Leaves and twigs move (Increased flapping of flysheet and unsecured tent flaps, with slight movement of poles during prolonged gusts.) 8-12
4 Moderate Breeze Raises paper moves small branches (Wind 'bulges' around poles, causing slight flexing of fibreglass poles. Ensure guy ropes are taut, and secure loose canopies or tarps) 13-18
5 Fresh Breeze Sways small leafy trees (Significant flapping and bulging of flysheet. Fibreglass poles flex noticeably during sustained gusts. Remove any tent extensions or utility tents. Regularly check and adjust guylines and pegs.) 19-24
6 Strong Breeze Sways large branches (Significant flapping and wind bulging of flysheet. Fibreglass poles flex by several inches in sustained gusts. Take down any tent extensions, utility tents etc. Frequently check guylines are taut and pegs remain in the ground.) 25-31
7 Moderate Gale Trees sway (Fibreglass poles flex significantly, and the tent's shape may become deformed. There's a risk of poles splitting.) 32-38
8 Fresh Gale Broken twigs, walking impeded (Movement on foot becomes difficult. If not in a low-level geodesic tent, consider packing up as conditions are potentially hazardous.) 39-46
9 Strong Gale Chimneys, slates, hoardings damaged  47-54
10 Whole Gale Trees Blown Down and Considerable damage 55-63
11 Storm Major Damage 64-75
12 Hurricane Very dangerous tropical whirling winds 76+