The recommended diameter for a climbing rope depends on the type of climbing you'll be doing. For general-purpose climbing, a diameter between 9.5mm and 10.2mm is commonly used. Thinner ropes (8.9mm to 9.4mm) are more suitable for advanced climbers seeking lighter weight, while thicker ropes (10.3mm to 11mm) offer enhanced durability and handling for rugged terrains or frequent use.