As the moon circles the earth in an ellipse the distance between them varies, at the nearest (perigree) it is 363,300 km and at the furthest (apogee) 405 355 km .
The size of the moon as seen from the earth will vary depending on the distance between them. The position of the moon in its orbit round the earth when it is full will determine its size. The nearer the apogee the smaller it will appear to be, the nearer the perigee the bigger it will appear.
The changing position of the full moon can be plotted as a graph:
A lot is known about the moon and it is the only heavenly body to have been visited by humans.This is a site providing up to the minute information about the moon.
Most of this knowledge has been gathered recently. Here is an entry in Arthur Mee‘s Children’s Encyclopedia written in 1930: