go over to happ for dimensions, they have dimensions for everything they sell. as for which is better, i've heard happ considered the industrial trackball, and ultimarc as the home enthusiast trackball. so if it's gonna get alot of play, and i mean alot, then get the happ. otherwise, the ultimarc is just fine. also, the ultimarc has plastic on the outside of it's rollers and the optics are plastic...and people say it isn't as smooth. quite frankly, i'd get the happs, but many people swear by the ultimarc one...