There is no set rule for where, or how high, to place a towel rack in the bathroom, although the layout of the bathroom can be your guide. A towel rack or hook should be within easy reach of the tub or shower, while a rack or ring to hang hand towels should be placed near the sink, typically higher than the sink top.
Height Range
The National Kitchen and Bath Association recommends hanging bath towel bars -- in most cases -- between 30 and 48 inches above the floor. The low end, 30-inch range works well if children share the bathroom. If you're double-stacking the towel bars, or if you use bath sheets that are significantly larger than the typical bath towel, you may wish to install the towel bars even higher than 48 inches from the floor. Towel hooks can be placed even higher than that, if especially if the hook is intended to hold a bathrobe. If bathrobes are part of the equation, position the hook so the bathrobe hangs from it without touching the floor. The best rule of thumb is to hang the bars or hooks at a height that makes sense for your bathroom layout and is comfortable for everyone using the bathroom.
Holders for Hand Towels
Whether you have bars or rings to house hand towels near the sink, position them so they can be reached while you stand at the sink. As for height, place the bars or rings so the towels can be hung without touching the countertop, sink or other furnishings in the bathroom. Use visual cues to help pick an ideal height and position for the towel bars; for instance, if the top of a freestanding bathroom sink is 35 inches above the floor, hang the towel bar or ring at the same height for continuity. If the bar or ring hangs over a countertop or cabinet, halve the height difference between a wall sconce and the countertop for another visually pleasing option -- if the sconce sits at 60 inches off the ground and the counter is at 30 inches off the ground, 40 inches may work well. Again, it's mostly a matter of personal taste as to what seems functionally efficient for you while still looking good in its space.