Found my own answer in the manual - 121 mm, barely bigger than my vv v3 but with 2-1/2 times the battery. Just bought the tube, battery, and control head - you have to shop around to get it much cheaper than the full kit, but I managed to do that and am now a happy new owner. Loving that it does USB charge/passthrough, collects myVapors stats, and feels and operates like a mini-eVic.