You likely won't find any strict guidelines for standard towel-ring height. The humble hand-towel holder -- or more so, the towel itself -- becomes an annoyance, however, unless you install it at a handy height and in a convenient location:
- Mount the ring high enough to keep the draped towel from touching the sink or vanity, with just a few inches to spare. If you mount the ring any higher, the towel can be difficult for small children to reach. Typically, vanities range from 30 to 36 inches high, but standard height is about 32 inches; in this case, 47 inches from the finished floor is a handy height for the ring.
- Keep the towel away from light switches or electrical outlets, which often are about 47 inches from the floor -- dripping hands and electricity are a hazardous mix.
- Install the ring out from a corner, instead mounting it toward the front of the vanity. If it's positioned to the back, it's again an awkward reach for a small person or someone in a wheelchair.
- Install the ring so that it doesn't protrude into or hinder a medicine cabinet's door swing or the direction it opens -- to the left or right.
Use a wall anchor to the ring, if there isn't a sturdy stud where you need one; otherwise, the hardware can eventually rip from the drywall, and the towel will end up in another inconvenient location -- on the floor.