BubbleScale Property
Returns or sets the scale factor for bubbles in the specified chart group. Can be an integer value from 0 (zero) to 300, corresponding to a percentage of the default size. Applies only to bubble charts. Read/write Long.
Example
This example sets the bubble size in chart group one to 200% of the default size.
With Worksheets(1).ChartObjects(1).Chart
.ChartGroups(1).BubbleScale = 200
End With