Hello Lee,

Thank you for posting in our forum.

To get the size of the dropdown button you need to get its UIElement. To do so you may use code like this:

var dropDownButtonElement = this.ultraDateTimeEditor.UIElement.GetDescendant(typeof(DateTimeEditorDropDownButtonUIElement));

var drobDownButtonSize = dropDownButtonElement.Rect.Size;

In the attached sample project I have implement this. Please check my sample and let me know if you need any additional information.

Thank you for using Infragistics Controls.