When top-roping is used how long should the rope be in order to protect climber throughout climb?

The length of the rope needed for top-roping depends on the height of the climb and the type of climbing being done. In general, the rope should be long enough so that the climber can reach the top of the climb and still have enough rope left to tie a knot at the anchor and lower safely to the ground.

For single-pitch top-roping, a rope that is 50 meters long is typically sufficient. This length will allow the climber to reach the top of most single-pitch climbs and still have enough rope left for tying a knot and lowering. For multi-pitch top-roping, a longer rope may be needed, depending on the length of the climb. A rope that is 60 meters or 70 meters long is typically sufficient for most multi-pitch top-roping routes.

In addition to the length of the rope, it is also important to consider the diameter of the rope when top-roping. The diameter of the rope affects its strength and weight. A rope that is too thin may not be strong enough to support the climber's weight, while a rope that is too thick may be too heavy and difficult to handle. A rope that is 9.5 millimeters or 10.5 millimeters in diameter is typically a good choice for top-roping.