How does the earth's moon compare to moons of gas giant planets?
Earth's Moon is smaller than the Ganymede, Callisto, Titan and Io.
Diameter of Earth's moon:
Ganymede (Jupiter's Moon):
Titan (Saturn's Moon):
Callitso (Jupiter's Moon):
Io (Jupiter's Moon):
All other moons are smaller than earth's moon.
For example: See image for the Jupiter's Moon Europa.