Trek routes in Nepal are graded according to altitude, elevation you rise in a day, & required skills.  Some divide the routes into five grades, while others like the lonely planet guide divide into three grades of easy, medium, and hard. Some of the routes are strictly of a particular grade, and others are of mixed difficulty of easy-medium, or medium-hard. The trek intermarries require you walk at least 4-5 hours a day to reach the day’s destination.

While you do not require any skill except physical fitness to trek on the easy & moderate grade routes below 3,000 meters, you need to allow your body enough acclimatization for the medium & hard grade trekking. The hard grade routes require a strenuous steep climbing with some mountaineering skills.

Here is an easy way to determine a region according to its difficulty:

The Everest Region & The Restricted Areas:
As the regions lies on a high altitude, all treks in these reasons are of medium & hard grades, or the medium-hard combination.

Annapurna Region:
All treks on this region are of easy & moderate grade. The Annapurna Circuit (Around Annapurna) falls in the hard grade.

Langtang & Helambu Region:
Ganja La is hard, Gosainkunda medium-hard, others easy-medium.