To use the Measure app, make sure you’re in a place with good lighting.
Open the app by pulling down on your screen and searching for “Measure”.
Follow any onscreen instructions that ask you to move your device around. This gives your device a frame of reference for the object you're measuring and the surface it's on.
Keep moving your device until a circle with a dot in the center appears.
Move your device so that the dot is over the starting point of your measurement, then tap the Add button.
Slowly move your device until the dot is over the ending point of your measurement, then tap the Add button again.
While the measurement is displayed, you can tap the number to see it in inches and centimeters. Tap Copy, and the value is sent to your clipboard so you can paste it into another app.
You can also take a photo that shows the object and its measurement. Tap the Shutter button, and the photo appears in the lower-left corner of your screen.