The new Measure app allows you to use augmented reality (AR) to measure lines using only the back camera of your iPhone. The Measure app works pretty well in a pinch if you find yourself without a tape measure near you.

Launch the Measure app from your Home screen.
Move the white dot to your start point. It will try to snap to corners when the camera comes across one.
Tap the + button to select your start point.

Move the white dot to your endpoint.
Tap the + button to select your…