Here are the names of the 3 largest moons in our solar system by diameter:

1. Ganymede (Jupiter) - 5,268 km (3,273 mi)

2. Titan (Saturn) - 5,149 km (3,199 mi)

3. Callisto (Jupiter) - 4,821 km (2,995 mi)

It's important to note that while these are the largest by diameter, Ganymede is also the most massive moon in the solar system.