How is the effort calculated?

This tool uses Naismith's rule (1892) adapted for running: add 1 minute per 10 m of elevation gain per km of horizontal distance (or equivalently, treat each 100 m of D+ as 1 additional km of flat distance).

Equivalent flat distance = horizontal distance + (D+ ÷ 100). This is the simplest and most widely used model for trail running effort estimation.

Example

A 20 km trail with 800 m D+: equivalent flat distance = 20 + 8 = 28 km. At a 5:00/km flat pace that's 2h20 instead of 1h40.

Limitations

Naismith's rule ignores descent (which costs energy too, especially technical terrain), surface conditions, and altitude. For technical trails use a modified factor of ÷70 or ÷80 for D+.