The bo staff is traditionally 6' long. Most modern bo practitioners use a bo a few inches longer or shorter than they are. A longer bo extends your reach, while a shorter bo is easier to manage. You may want to order one a little bit longer than you think. You can always trim it down later. Ask your instructor for exact measurements he may recommend for your particular style and body frame.
Other measurements for a jo staff are your measurement right below your armpit.
We offer 3 round sizes. The 1", 1-1/8", and 1-1/4".
The 1" is a good size for quickness and standard training.
The 1-1/8" is a bit heavier. Its feels comfortable in most people grip. Its a good compromise of strength, impact force, and speed.
The 1-1/4" being the heaviest is good for stronger people and larger hands. Its very strong and used in groups that do more training that required harder blade impact. This is typically selected as a quarterstaff for western martial arts and no so much as eastern martial arts. Its extra weight makes it slower, but also hits harder. Be careful.
We offer octagon as well. These feel very nice in your hand. The 1-1/16" had a solid martial feel to it. Good for solo training and personal protection. I don't recommend steady impact training with it, since the angle can wear down quicker than a round staff.
The 1-1/2" octagon is a monster. This is only used for specialized martial training. They require a larger grip and strength (or fitness) to use.