What size bo staff is best for me? This is a very common question, and it is very easy to answer. Your ideal bo staff should be approximately the same size as you. If that is all you were looking for, then you can stop reading here. If you want to know WHY, then please read further!
The why, of a proper size bo staff is a little more complicated, but I think anyone can understand it. After all... lets say you just read my answer above, and then say to yourself, self, how about a just use a bo staff that is a foot bigger then me?! Why not! Well... of course you can do whatever you want, but to understand why I say a proper 'self sized' bo staff is best I need to explain some physics in terms of martial arts.
First off, just know I am a seasoned black belt, who has been making staffs for around 8 years now, and I have a degree in physics, and taught physics at all levels for 10 years. So that is who is anwering this question, and I doubt that many others would have the qualifications to answer it in the way I am about to. So here we go!
To understand the way a staff works, you need to understand torque. Torque, in physics is a force that pushes on something that makes it rotate. For instance, think of a merry-go-round at the playground. To make it spin you push it to the size and it starts to spin. The bo staff is the same. To swing it, you apply two torques. One is from the top hand and the bottom hand. (Or left and right hand) One hand pushes while the other pulls. And this gives the staff the perfect swinging pop feel.
Now lets add another concept. (This is physics 101 by the way) The concept of weight. As you can immagine, if the merry-go-round is very heavy. Lets say 10 heavy construction workers are sitting on it, and you give it that same push to the side (torque) it will move, but MUCH slower. The staff is the same way. A heavier staff will accelerate (speed up) slower because the weight or mass of it resists the torque that you apply.
And now the final concept needed, to explain why your staff should be your size. The final concept is the length of the staff. If you immagine our merry go round once again, lets say you can stand in the center of it, like a carousel, and you can push near the center or near the edges. Where would you push to get it to move the fastest? Of course you would push it at the edge! Immagine if you pushed near the center. It would be very hard to get moving. This in physics is called, Rotational inertia. Its a fancy word that means, how much an object resists rotating. A big truck needs a HUGE engine to get it moving, because it has a lot of weight or inertia. But objects that you want to make spin have their own intertia too. Rotational inertia. You already know one of the factors that makes an object resist spinning. And that is its mass. But what is the other? Think of the caroucel example we just gave! And where you would want to push it.
Thats right! If you push it toward the center, it would become almost impossible to get it to rotate. But if you push it more toward the outside, its much easier. Does that seem to start making sense for staffs yet?
Ok, lets finally answer the question. Immagine your staff, and forget about the weight, thats easier to understand. But think of a super duper long staff and you are holding it. Its WAY longer then you. Your arms are more toward the center then with a shorter staff. Therefore when you give it a push, you have MUCH less effect on making it accelerate with any speed then you would if your hands were further out. In fact, its not just less, its a LOT less. Also... lets immagine someone is striking your staff at the dojo. If your staff is huge, the OTHER staff is now trying to make your staff rotate. In fact it could rotate right out of your hands. If your staff is HUGE and they hit you at the end, there is MUCH more torque from the other staff and you have to hold on MUCH tighter, if you even can. In other words, your gigantic staff is more of a liability than an asset if you are swinging it, and not using it just like a spear.
On the other hand, if your staff is too small, now your hands are more toward the edges. So when you go to swing the staff the end of the staff, is moving more at the speed of your hands, and you don't get that snap you want. There is a sweet spot where the staff accelerates just right, has the perfect reach, and has enough control to take and give hits without being unstable. And that is when its at your own body height.
No matter if you are small or large, to develop proper technique, trust your body, let the staff fit to your size and let your body develop your best technique.