The moon came within about 221,802 miles from Earth last night. That is about 15,300 miles closer than average.
That proximity made the moon appear about 14% bigger than it would if the moon was at its farthest distance, said Geoff Chester of the US Naval Observatory.
The difference in appearance is so small that "you'd be very hard-pressed to detect that with the unaided eye," he said.
The moon's distance from Earth varies because it follows an elliptical orbit rather than a circular one.
Like any full moon, the supermoon will look bigger when it is on or near the horizon rather than higher in the sky, thanks to an optical illusion, Mr Chester said.
The supermoon will bring unusually high tides because of its closeness and its alignment with the sun and Earth, but the effect will be modest, he added.
But no matter how far away a full moon is, it's not going to make people commit crimes, get admitted to a psychiatric hospital or do anything else that popular belief suggests, a psychologist said.
Studies that have tried to document such connections have found "pretty much a big mound of nothing, as far as I can tell," said Scott Lilienfeld, of Emory University.
Mr Lilienfeld, author of 50 Great Myths Of Popular Psychology, said the notion of full moons causing bizarre behaviour ranks among the top 10 myths because "it's so widely held and it's held with such conviction".
He said a key reason could be the way people pay attention to things. If something unusual happens to occur during a full moon, people who believe the myth take note and remember, even telling other people because it confirms their ideas.
But when another full moon appears and nothing out of the ordinary occurs, "they're not very likely to remember" or point it out to others.
So in the end, he said, all they remember are the coincidences.