We have a very useful size guide available for you, including a size generator. We also have our models' measurements (underbust, bust, waist, hips) displayed on each product page. However, if you have specific questions about your size please contact info@louswim.com.
Please note the FIO bikini top runs small so we recommend you view the information we have on the band size and maximum stretch to see what size will fit you best and whether you need to size up. For example if you are 71cm underbust usually you are a size XS but a size XS FIO top is 64cm band with 72cm at maximum stretch so we would recommend you size up to a size S.