The size of a wash basin for a 4-foot countertop can vary depending on personal preference and available space. However, a standard recommendation is to choose a wash basin with a width of around 16 to 20 inches (40 to 50 centimeters). This width provides sufficient space for washing hands comfortably while leaving enough countertop space for other items.
Keep in mind that the depth of the wash basin should also be considered. A typical depth for a wash basin ranges from 4 to 6 inches (10 to 15 centimeters), although deeper options are available. Consider your specific needs and the overall design aesthetics when selecting the depth of the wash basin.
It's important to note that these are general guidelines, and you should measure your countertop and consider your personal preferences before making a final decision.