If your kitchen bar area is multipurpose and will be used for a variety of activities by people both sitting and standing, aim for a height between 36 and 38 inches high. This provides enough room for people of almost any height to use the bar surface comfortably, including — with the help of a chair — children. It is also an ideal height for working in the kitchen.
The standard bar is much higher than a typical kitchen countertop. If you want the traditional bar look and feel, plan on making the area between 42 and 46 inches high. This allows people to either sit or stand at the bar when drinking. Space is also important in this situation: a good bar needs at least 16 inches of width to hold drinks and plates, more if someone will be using the other side of the bar as well.
You can also choose to make your bar a midlevel size. This particular height is common for home and patio uses where you want to compromise between the two heights. Bars this size are usually 40 to 42 inches high. While it may be more difficult to find examples of this height, it may also be your "best of both worlds" solution, a height that appeals to everyone.
When choosing your bar height, keep in mind the surrounding fixtures as well. Bar stools need to be adjusted to the height of your bar. A traditional bar, for example, needs stools that rise between 32 and 35 inches high. The light fixtures above the bar are also important and must be high enough from the bar to not get in the way.