Figure out how you plan to use the bar to envision the basic shape. Create a large square-shaped bar, for example, if you want to play board games there after dinner. You might want to build a round bar if you will eat most family meals there. A rectangular island bar built for food preparation and eating will work if your kitchen is extremely large.
The height of the bar should harmonize with other counter space. Create a bar 6 to 12 inches higher than standard 36-inch countertops, for example. But make sure you want to use the taller stools required for a higher bar top. Also, sketch the new bar space from every angle, because a higher bar may stand out negatively, especially in a small kitchen.
Bar overhang space is a requirement. The typical overhang is 12 inches. If you plan a rectangular bar to seat people on three sides, for example, make the bar 6 feet long by 3 feet wide. To seat people on all four sides, you might make this 6-foot bar 4 feet wide instead. Build the bar at least 42 inches high.
Odd shapes require thinking through dining space. If you want to create a circular bar, for instance, keep in mind that knee room underneath plays into the picture. Diners seated around a bar might do well with a 12-inch overhang. But, allowing 18 inches of overhang will be more comfortable. Envision a bar 5 feet in diameter but plan the support structure in the middle with care. A large round bar can topple if its center support is not attached firmly to the kitchen floor.
Pay attention to "elbow room" needed by those dining at the bar. If you want to plan a bar for six people that is very narrow, you should allow 2 feet of width along the length of the bar for each person. This means you will need to construct a bar 12 feet long, which may not be practical. Using a square shape of 4 feet square or 5 feet square might work better. You can seat two people on at least three sides of the bar and allow for a 12-inch overhang.