Option(Mac)/Alt(Windows)+drag the layer:
When you hold down Option (Mac)/Alt (Windows) and drag a layer, Photoshop will display the guide lines and distance between the original layer and the copied layer. This feature can be used together with the Move and Path selection functions.
The distance between the original layer and the copied layer
Hold Cmd (Mac)/Ctrl (Windows) + hover over the layer:
When you hold down Cmd (Mac)/Ctrl (Windows) and hover over a layer, you can see the guides and distance between them. Select a layer, then hold down Cmd (Mac)/Ctrl (Windows) and hover over another layer, which can also be used in conjunction with the arrow keys to nudge the selected layer.
Measurement guides when working with layers
Path measurement:
When working with paths, measurement guides appear in Photoshop. Measurement guides also appear when you select the Path Selection feature and drag a path within the same layer.
Path measurement
The distance between the canvas and the canvas:
When you hold down Cmd (Mac)/Ctrl (Windows) and hover outside a shape, Photoshop displays the distance between the shape and the canvas.
The distance from the canvas
Matching spacing:
When you copy or move an object, Photoshop displays measurement guides to clearly show the distance between the selected object and its neighbors.
