Most long boards are ranged between 90 to 150 cms and it depends entirely on the application by the user. A 100 to 130 cm board is for transporting or commuting from one point to the other on the concrete floors. It is easy to ride and comfortable to use. They resemble the shape of a surfboard and are also used for cruising.
The Slalom skateboards come in 63-89 cms and are used mostly for racing. For that very purpose, these long boards are made of carbon fibre for durability. In this, the trucks are very narrow and located at the very end of the board, allowing it a tighter radius. Even the wheels are much larger so that during the slalom situation, the skater will get better traction. If you are into competitive skating, then slalom long boards are the ones you choose for better practice.
If you want to enjoy a ride downhill, then choose long boards in the range of 95-110 cms. These are long and rigid. Downhill long boards have lowered platform with a deck below the base plate of the axles. This provides better gravity and allows for more control while going downhill. If you are an expert, you would have attached streamlined helmets to decrease the drags.
When you want to show your excellent skating skills, then it is recommended for you to use longboards. Since these are longer than the common skateboard, you can easily control the maneuvering. The size ranges from 150-200 cms. On the other hand, trick boards are not longer than 100 cms.
Another sports that you should try is wakeboarding.