You should have approximately 25-30cm of free space between the seat and the underside of the bar/counter top for your legs to comfortably fit.
Measure the height from your floor to the underside of the bar/counter top then subtract the space for your legs (25-30cm) to determine the optimal seat height.
A product's measurements can be found in the features list or image gallery. If additional information is required our customer support team can be reached via the "Contact Us" page or "Live Chat".