You measure a rectangle or ellipse by using the Rectangle tool or the Ellipse tool, as applicable.
Tip: Make sure you have the right area unit of measure selected.
To measure a rectangle or ellipse
Zoom or pan the image, as necessary, to the area of interest.
On the toolbar, click the arrow beside Measurement Tools, and then on the menu that appears, click Rectangle or Ellipse, as applicable.
In the view pane, do the following according to the tool you selected:
With a rectangle, drag to draw a rectangle over the area you want to measure, and then double-click to stop.
With an ellipse, drag to draw an ellipse from the center of the area you want to measure outwards to cover the area you want, and then double-click to stop.
The area and perimeter of the rectangle or ellipse are displayed on the status bar.