You will need to measure the entire length of the spring, including the coil and hook at either end.

If you have a round trampoline you measure the diameter of the frame in terms of the distance from one side of the trampoline to the other from the outer frame, not from the size of the trampoline mat.
If you have a rectangular trampoline you count the amount of springs along the length and breadth of the trampoline. It is also good idea to measure the jumping mat as well.

Yes they are, however this does not mean they will last forever. Your product frame, net, safety padding or mat will deteriorate eventually and will need to be replaced. Product longevity can also be dramatically effected by factors including but not limited to location of installation (direct sun vs shaded area, higher temperature environments), proximity of location to coastal environments (salt spray), and close proximity to swimming pools (corrosive).

Larger play equipment items like trampolines and swing sets can take up a large area. A safe and clear area, normally recommended at around 2 metres, is essential around all sides of the play equipment. Assembled dimensions are available and listed in product details and on their packaging. If there is a specific product of interest call 1800 777 137 for assistance or email sales@actionsports.com.au. There is also additional information provided on the trampoline buyers guide on this website.