The Vertical Index indicates how much climbing you will face on average per kilometer. The calculation is simple:

Vertical Index = number of positive elevation meters ÷ number of kilometers

A trail of 20 km with 1,000 elevation meters has, for example, a Vertical Index of 50

The higher the Vertical Index, the more you have to climb on average per kilometer and the tougher the course usually is. This allows you to quickly compare trails of different distances with each other and better estimate what awaits you along the way.