Two ways to measure
- Bullseye (lay flat): put the phone screen-up on a table, desk, washing machine or shelf to see the tilt in both directions at once.
- Bar (stand on edge): stand the phone on its long side or bottom edge against what you are checking, such as the top of a picture frame, a shelf or a curtain rail. It works in portrait or landscape and picks the nearest edge automatically.
Like a real spirit level, the bubble floats to the higher side: a bubble on the right means the right side is high. Within 0.5° it turns green, and phones that support it give a short buzz.
What an angle means in millimetres
Height difference = length × tan(angle). A few handy numbers:
| Tilt | 60 cm shelf | 1 m table | 2 m rail |
|---|---|---|---|
| 0.5° | about 5 mm | about 9 mm | about 17 mm |
| 1° | about 10 mm | about 17 mm | about 35 mm |
| 2° | about 21 mm | about 35 mm | about 70 mm |
So a 1 m table reading 1° is out by 1000 × tan 1° = 17.5 mm; raise the low leg by about 1.7 cm.
Calibrating for accuracy
A camera bump can make a phone lying on its back sit slightly crooked. On a surface you trust, tap Set current position as 0 and the level subtracts that offset from then on. The calibration is saved on this device.
To check it, turn the phone 180° in the same spot. If the reading matches, you are accurate; if not, true level is halfway between the two readings. It is the same reversal test carpenters use on a spirit level.
If it does not work
- iPhone and iPad need permission for motion sensors. Tap Start level and choose Allow. If you denied it, turn on Settings → Safari → Motion & Orientation Access.
- Computers rarely have a tilt sensor. Scan the QR code shown on screen to open the page on your phone.
- Jumpy numbers: set the phone down instead of holding it and give it a second. Tap Hold reading to freeze the value.
Phone sensors are typically good to about 0.1–0.5°, which is fine for furniture and picture frames. For tiling or window fitting, confirm with a real spirit level.