double heightFactor

If non-null, the factor of the incoming height to use.

If non-null, the child is given a tight height constraint that is the max incoming width constraint multipled by this factor. If null, the child is given the incoming width constraints.

Source 

double get heightFactor => _heightFactor;
void heightFactor=(double value)

Source 

set heightFactor (double value) {
  assert(value == null || value >= 0.0);
  if (_heightFactor == value)
    return;
  _heightFactor = value;
  markNeedsLayout();
}