symbol.size()

symbol.size([size])

If size is specified, sets the size to the specified function or number and returns this symbol generator. If size is not specified, returns the current size accessor, which defaults to:

function size() {
  return 64;
}

Specifying the size as a function is useful for constructing a scatterplot with a size encoding. If you wish to scale the symbol to fit a given bounding box, rather than by area, try SVG’s getBBox.