How big is Neptune?

Neptune is the fourth largest planet in our Solar System and it is the smallest of the giant gas planets. Neptune has a diameter of 30,598.8 miles (49,244) kilometers. Its volume is 57.7 times the volume of Earth which means that 57 Earths could fit inside of Neptune with a little room left over. 

NASA has much more information about Neptune, see: https://science.nasa.gov/neptune/ .