The development of climbing rating systems came about during the late nineteenth and early twentieth centuries in Britain and Germany. The ratings used internationally today include four for alpine climbing, four for ice and two for aid climbing. Though bouldering was originally just a game that alpinists enjoyed, bouldering as a sport in itself has become popular worldwide. John Gill created the B-scale to rate bouldering routes and problems, and John Sherman created the V-scale which gives permanent ratings unlike the B-scale.
B1 and B2
The B1 on the B-scale requires moves that are at a skill level of 5.12 or 5.13 on the Yosemite Decimal Scale (YDS) which is the scale used for rating the hardest moves required on a rock climb. The B2 on the B-scale according to "Mountaineering: The Freedom of the Hills" constitutes moves as hard as 5.15. This is as hard as it gets.
A B3 bouldering climb is a successful B2 climb that has not been repeated. If it is done more than once, the rating goes back to B12.
V0- to V6
The B-scale has ratings that float somewhat but the V-scale gives precise ratings that are comparable to the YDS. V0- is equal to a 5.8 on the YDS, a V0 is equal to a 5.9, V0+ is equal to a 5.10a/b, V1 is equal to a 5.10c/d, V2 is equal to a 5.11a/b, V4 is equal to a 5.12-, V5 is equal to a 5.12 and a V6 is equal to a 5.12+.
V7 to V15
The Sherman V-scale continues to include V7 which is equal to a 5.13-, V8 which is equal to a 5.13, V9 is equal to 5.13+, V10 is equal to a 5.14-, V11 is equal to a 5.14, V12 is equal to a 5.14+, V13 is equal to a 5.15-, V14 is equal to a 5.15 and a V15 is equal to 5.15+.