Metaphoric gesture used to show size with both arms outstretched, depending on the nuance you want to convey
Hands/Arms: Both arms are extended out to the sides, palms facing forward with distance between your fingertips represents the size being described.
Intensity: The intensity of the gesture can reflect the perceived size. More dramatic arm movements can depict something truly massive.
Context: These gestures are often accompanied by verbal descriptions or facial expressions to further emphasize the size being conveyed.
The fish I caught was this big!