You can use the Dimension tool 
to measure the distance between two points and visualize the distances in your artwork.
to measure the distance between two points and visualize the distances in your artwork.How to visualize distances
1. Select the Dimension tool from the Tools panel.
2. To measure the distance between two points, drag a line from one point to another.
3. To measure the vertical or horizontal distance between two points which are not aligned, hold down the Shift key and drag a line from one point to another.
4. Select the Round option on the control panel to round off the measured distance to the nearest whole number.
5. Specify the size of the text in the dimensions box.
6. Specify the size of the arrow.