You need to decide on length based on your unique requirements. Typically speaking, you have to allocate at least 2 feet of length for every seat you are planning to add. If you want to build a basement wet bar with four seats, you have to keep the bar 8 feet long. The extra space you create helps people move around the bar easily. You should have enough space to move items in and out quite freely. This method of approach helps you avoid blocking doorways.