Measure Tool is just below the shape tools and beside the pen tool.With the help of Measure Tool we can calculate the distance between any two points in the work area.When we measure from one point to another. we can see a nonprinting line and options bar and information palette in which we can see starting X-location, Y-location,

horizontal and vertical distances travelled from x and y axis, total distance travelled. This is the Measure Tool.Just go onto this tool and click on it to select it.
For example, we have imported this image.We want to measure its length.
Now Select the measure tool and drag from starting point to ending point like this.We can see all its informaton in the options bar.

Water Mark Image  | Gradient Tool  | Marquee tool  | Crop tool  | Move tool  | Magic tool  | Lasso tool  | Anchor Point tool  | Clone Stamp Tool  | Color Sampler Tool  | Custom shape tool  | Ellipse Tool  | Eye Dropper Tool  | Hand Tool  | Measure Tool  | Pen Tool  | Polygon Tool  | Rectangle Tool  | Rounded Rectangle Tool  | Zoom Tool  | Convert Point Tool  | Free form pen tool  | Delete Anchor point Tool  | Making an EyeBall  | Creating a 3DBall  | Removing Background of an Image  | Creating a Glassy Button  | Creating Impression Effect