This system evaluates the overall difficulty of a route based on factors such as length, altitude, cold, exposure, danger, commitment, and technical difficulty. Originally based on UIAA Roman numerals, it now commonly uses French letters and is widely adopted globally.

• F (Facile/Easy): Simple rock scrambling or easy snow slopes, some glacier travel. Often climbed ropeless except on glaciers.
• PD (Peu Difficile/A little difficult): Some technical climbing and complex glaciers.
• AD (Assez Difficile/Fairly hard): Steep climbing or long snow/ice slopes above 50 degrees. Suitable for experienced alpine climbers only.
• D (Difficile/Difficult): Sustained hard rock or ice climbing, or snow slopes. Serious challenges requiring technical skill.
• TD (Tres Difficile/Very difficult): Long, serious, and remote climbs with high technical difficulty.
• ED (Extremement Difficile/Extremely difficult): The most challenging climbs with continuous, high-level difficulties.

Fitness Levels

• Basic Fitness (F/PD): Suitable for those with good basic fitness, such as Munro-bagging. Average rucksack weight: 6-8 kg.
• Good Cardiovascular Fitness (AD/D): Requires solid cardio fitness, achieved through hiking, running, or gym work. Average rucksack weight: 8-12 kg.
• High Fitness (TD): Requires a high level of fitness, physical toughness, and the ability to carry a heavy rucksack for extended periods. Average rucksack weight: 12-18 kg.
• Extreme Fitness (ED): Requires extreme physical effort and preparation, often at high altitudes. Some weight loss is inevitable, and long-term fatigue may follow. Extensive training is essential.