'Unique product' For extra coverage and sun protection. I wear these daily for teaching in and am very impressed with their durability. I would choose to swim in them now too.
A couple of measurements that might help:
Size 8 (approx) = Waist: 64-78 cm Inside Leg: 72 cm
Size 10 (approx) = Waist: 66 - 84 cm Inside Leg: 75 cm
They sit on the waist (not down on hips) and have a drawstring.