The centre of these fins flexes to fit people both with and without their wetsuits. You just need to check that you select long enough straps to fit over your wetsuit too. So in warmer water, you can wear them without a wetsuit. When the water is colder, you can adjust the straps to wear them over a wetsuit. The fins still fit. The straps go around the narrowest part of your leg, just above your ankle. So, please measure the circumference around this narrowest part whilst wearing your wetsuit. If this circumference is 20-40 cm (8-16 inches) then the standard straps supplied with the fins will fit you. If this circumference is larger than 40 cm (16 inches), then just select the option for longer straps when you order your fins. If you prefer to measure your leg circumference without your wetsuit, then just add the following to your measurement to compensate. For a thin 3mm suit add 2 cm (1 inch). For a thick 8mm suit add 5 cm (2 inches).