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How to use your iPhone as a bubble level

Open Device Monitor, Diagnostics > Motion Sensors > Bubble Level, lay the phone on the surface. The bubble and the Pitch (Front/Back) and Roll (Left/Right) angles update live; both inside about 1.1° and the screen says LEVEL ✓.

3 min read · Updated 2026-10-06

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When a phone level is good enough

Hanging a picture. Levelling a shelf. Checking why a table wobbles. Setting the feet on a washing machine or a camera tripod. For that kind of small job at home a phone is plenty accurate, and it's already in your pocket. For building work with a real tolerance written down somewhere, it is not a substitute for a proper spirit level - don't pretend otherwise.

How to use the iPhone as a spirit level, step by step

  1. Open Diagnostics, tap Motion Sensors, then Bubble Level. It starts itself; nothing to press.
  2. Flat surface - table, shelf, appliance top - lay the phone on it screen up. Watch the bubble drift toward the centre.
  3. Read Pitch (Front/Back) (tilt along the phone's length) and Roll (Left/Right) (tilt across it), both in degrees to one decimal.
  4. Nudge the surface until both sit close to 0.0° and the status flips from Not Level to LEVEL ✓.
  5. Picture frame or shelf edge? Rest the phone's long edge on it and watch the angle move as you tilt the frame.

What LEVEL means in numbers

The app reads the phone's attitude from iOS 30 times a second and converts radians to degrees. LEVEL ✓ shows once pitch and roll both drop under 0.02 radians, which works out to 1.1°. Yaw (Rotation) is just which way the phone points on the surface - it plays no part in the verdict.

Two readings and the verdict the app gives
Pitch (Front/Back)Roll (Left/Right)Status
0.9°-0.7°LEVEL ✓
2.0°0.2°Not Level

The first reading passes because both angles are inside 1.1°. The second fails on pitch alone: 2.0° front to back is almost twice the tolerance, even though the roll is close to zero.

Is the iPhone level accurate?

The motion sensors are the same ones iOS uses everywhere, and the number holds steady to a tenth of a degree. The weak link is the phone itself, not the sensor: there's no calibration or zero button here, so a thick case, a camera bump or a curved back can rock the phone and quietly add its own tilt.

Check your phone for bias in 30 seconds

  1. Lay the phone on a flat surface, note pitch and roll.
  2. Turn it 180° on the same spot, so the top now sits where the bottom was.
  3. Read again. On a genuinely level surface both readings land about the same size with the sign flipped; a difference between them is coming from the phone or its case, not the surface.
  • Pull the case off for small jobs, or rest it on its flat edge instead of its back.
  • A camera bump tilts the phone when it lies screen up. Slide a thin card under the opposite end, or measure on the edge instead.
  • Apple's own Measure app has a level too, reading the same sensors - use whichever is already open.

Questions and answers

Is the bubble level free?
Yes, Bubble Level is in the free version of Device Monitor.
Can I calibrate the level?
No calibration option in the app. Run the flip test above to see how much your phone or case is adding, and pull the case off for a steadier reading.
Why does it say Not Level when the surface looks flat?
The tolerance sits around 1.1°, a slope small enough that your eye won't catch it. A camera bump or case can account for part of that too.
Does it work on iPad?
Yes - same motion sensors on iPad. Lay it flat, read the same two angles.

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