The Aqualogix fins work up to about 12.5” in circumference. If you are needing larger than that, you can check out our Aquastrength Fins as those can be adapted with extra straps to work with even greater circumferences. The same can be achieved with the Aqualogix Hybrid Fins, you can purchase an additional maintenance kit and “daisy chain” the two strap sets together to make a larger combined unit as shown below.