To measure the distance between different layers on the Canvas, select the first layer, hold ⌥ and hover over the layer you want to measure against. To measure against a layer that’s inside a group, you’ll need to hold ⌘ as well.
If you’re measuring the distance to a text layer, holding ⌥ will measure to the text’s bounding box. Holding Ctrl will measure to the text’s baseline (from the bottom) or cap height (from the top).
You can change the color of Sketch’s measuring guides under the Canvas tab in Preferences.
Measuring with Smart Guides and Snapping
As you move or insert layers and Symbols on the Canvas, Sketch will automatically show you measurements against nearby layers, as well as Smart Guides that help you snap to a nearby layer’s centre or edges.
If you have two or more layers next to each other, and move another near to them, Sketch will highlight their distance and automatically snap that layer to distribute them all equally.
When you resize a layer, if there are similar layers nearby Sketch will show you if they have a similar width or height. This also works when you’re resizing a layer that’s overlapping another.
Finally, when you insert or move text layers, they’ll snap to the height or width of nearby layers. Adjusting the height of a text layer will also snap the bounding box to the last line of text.
By default, smart guides are enabled in Sketch. To turn them off, choose View › Canvas › Show All Guides in the menu, or hold down ⌘ when dragging, to ignore them.