The iPhone’s Level used to be hidden inside the Compass app. Now (if you’re using iOS 12 on an iPhone SE, iPhone 6s or later, iPad 5th Generation or later, or iPad Pro) it’s hidden in the Measure app. It’s still very useful and super-handy, once you find it. Hang your pictures perfectly, get your table level, settle arguments about whether that wall is leaning or not.
To use the Level you have to first start the Measure app, so do that. Then, look for the “Level” icon at the bottom right of the screen. Tap that, then put your iPhone on edge and you’ll see something like this:
If you lay your iPhone down flat, on a table or perhaps the floor, you’ll see something like this:
When your iPhone is level on edge, it looks like this:
When your iPhone is laying flat on a level surface you’ll see something like this: