The V scale or Hueco scale is a method of rating the difficulty of bouldering problems. Created by John 'Vermin' Sherman (hence V) at Hueco Tanks, the V Scale differs from other systems such as the Yosemite Decimal Scale in that it (in theory) only takes into account the difficulty of the crux (hardest section) of the problem, ignoring factors such as length and exposure.

A rating in the V scale consists of an integer and an optional + (for higher difficulty) or - (for lower difficulty) suffix. The lowest rating on the V scale is V0-, though some people use "VB" to indicate a problem as easy or easier than V0. The scale progresses to V0, V0+, V1, V2, V3, and so on, with no defined upper limit. The + and - distinction is usually only applied to problems in the V0 to V1 range as harder problems are less easily classified with such precision.

The current highest rating of the scale is V16, accomplished by Dai Koyamada at the Wheel of Life problem in Australia, though this classification is contreversial.

As a point of reference, many beginning climbers in reasonable physical shape may be able to climb a V0- problem within a week of starting climbing (or immediately if they have experience in related sports). Most climbers without prior training require several months of practice before being able to complete a V1 problem.

References

http://www.camp4.com/bouldering.php?newsid=148