Looking to buy a climbing rope?  Here's a primer on what to look for:

Quick Stats:

Type:  Dynamic Kernmantle Single Rope
Coating:  Dry Coating
Diameter:  9.8mm - 10.5mm
Length:  60m or greater
UIAA Falls:  Higher the better
Impact Force:  Lower the better
Elongation:  Lower is better

Details:

Type:

For general sport climbing you want to make sure that the rope is dynamic, of kernmantle design and is rated a single rope.  Most climbing ropes are of kernmantle design, however, you want to look carefully to make sure that the rope is dynamic NOT static as they can look alike.  Dynamic ropes have stretch to allow for less force transmitted to the body in the event of a fall.  Static ropes are more typically used for things like extending anchors and more specialized climbing.  Also, be careful to examine the rope and make sure it is a single rope as opposed to a half or double rope.  All ropes should have a label at each of the ends.  For a single rope, there will be a number "1" printed on this label.  Halfs will have a "1/2" and doubles will show an infinity symbol.

Coating:

A dry coating helps keep the rope dry in the presence of moisture.  Although not absolutely required since non-dry ropes are a bit cheaper, the dry coating also helps to extend the life of the rope buy resisting abrasion.

Diameter:

Standard diameters range from 9.8mm to 10.5mm.  There is a direct correlation between the diameter and the number of UIAA falls (see below) that the rope can withstand.  However, larger ropes weight more and have more resistance through carabiners.  For the beginner belayer this resistance can be helpful.  This can also be helpful top roping as the resistance through the anchor would be higher.  However, for the lead climber, the increased rope drag can make clipping a little bit harder.  As for the weight, keep in mind that often the climbing wall will be on difficult approaches or at the end of a hefty hike.

Length:

The minimum length for a rope should be 60m.  This will give you enough rope for a vast majority of sport climbs.  There are climbs where this may not be long enough but longer ropes mean more weight and higher cost.  If length becomes and issue, two ropes of similar diameter can be joined together with the proper knots.

UIAA Falls:

The UIAA falls number is a rating that describes the number of factor 2 falls the rope can sustain before becoming unsafe.  A factor 2 fall is a worst case scenario and you are most likely to never come near this in typical sport climbing.  Basically it boils down to the rope being able to handle a 180lb weight dropped 15' with a 9' section of rope and produce less than 2700lbs of force multiple times.  This is a pretty severe test.  A higher number in pratical usage means the rope will last longer.  You will see that the diameter of the rope has a big impact on this number.  The larger the diameter, the larger the UIAA number (typically).

Impact Force:

The impact force number (rated in kilonewtons) describes the amount of force transmitted through the rope in a factor 2 fall.  Since the climber will be at the end of the rope this means that this force is transmitted to the climber.  Obviously, minimizing this force is very beneficial.  Keep in mind that in general sport climbing you will not come near a factor 2 fall but it's still good to have a low impact force.  However, lower impact force ratings generally mean a stretchier rope.  Stretchy rope is not necessary bad but if you need to take a break in the middle of a climb you will stretch downwards a bit and may have to climb back up to where you were.

Elongation:

The elongation rating describes the amount of stretch in the rope when weight is put onto it.  As described above in impact force, a higher elongation generally means lower impact force.  The number is a percentage and shows the amount of stretch on the whole length of a rope.  So a 10% number on a 60m rope means upwards of 6m of stretch, that's approximately 10'.

Other factors:

Other factors to keep in mind is to look for a rope with some sort of middle marker.  The middle marker visually shows the middle point of the rope.  Some ropes have a black mark or different colored fibers at this location.  Others will have two different colors or patterns for each half of the rope.  Where the color or pattern changes is the middle point.  This will become very useful for more advanced climbing and rappelling although not absolutely required.

- Brian