If you can imagine it, we can make it (almost). Unlike others, we have no "standard" sizes and most every ofuro we have made over the last 20 years has been customized to the needs and desires of the client in one way or another. We've made them as small as 2' x 2' x 2', and the largest we currently offer is 5' x 5' x 4' deep, or 6' x 4' x 4' deep (note that the "depth", is less that the actual overall height). The "typical" inside depth is 26" to 28" where upon you sit on the floor, but it's not uncommon to make them deeper, up to 48" deep, and have a bench for seating.
The thickness of the ofuro's sides is generally dependent on the depth. As the depth increases, so does the wall thickness. Up to 28" deep the thickness of the sides is a full 2". Over 28", up to 36" deep, the thickness increases to 3". Over 36" deep, the thickness of the sides is 4".
There are many different ways to determine what size ofuro will be most perfect for you. For many it's simply a matter of filling an existing building's space. Others want to completely customize it to their bodies. The one dimension that's most important for each individual is the depth. Too shallow and you lose the full relaxation effect, too deep and you wont be able to see over the side of the ofuro (which can cause an uneasy feeling of entrapment). Determining the perfect depth for you is quite easy. Simply sit on the floor, straight upright against a wall and measure from the floor to just above your shoulders. This measurement, give or take an inch or two, should be ideal for you (remember, if you slide away from the wall, and lean back, you'll sink lower into the water.)