Most countertops are 36 inches high and will accommodate bar stools, or chairs that are slightly higher than dining chairs. A comfortable clearance for people's knees below these countertops is 15 inches. Stools for raised 42-inch countertops are usually between 28 and 30 inches tall, giving a comfortable 12 to 14 inches of knee room. The recommended counter overhang also varies with the counter height, with experts suggesting 15 to 18 inches for the lower counter and 12 inches for a raised counter. Whatever height counter you have and whichever kind of seating, allow at least 24 inches of space between each seat for your guests' comfort. Don't forget clearance for furniture close to the countertop as you should allow at least 32 inches from the edge of the countertop to anything behind the seating area.
link:
http://homeguides.sfgate.com/much-clearance-needed-undercountertop-seating-83614.html
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White trim
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