How accurate is a phone level?

A good builder's spirit level is accurate to about 0.5 mm per metre (0.03°). A phone sensor, after calibration, is typically within about 0.1–0.2° – roughly 2–3 mm per metre. Loodis shows the reading to 0.1°.

That is much finer than you can see by eye: most people only notice a tilt from about 0.5°.

• Sensor offset – each phone's sensor is mounted a little off. Calibration removes it.
• Case and camera bump – they tilt the phone. Calibrate with the case on, and use the back calibration if you measure with the phone on its back.
• Rounded edges – used on its side, the phone rests on curved edges. Side calibration (Pro) handles that.
• Noise – a sensor reading wobbles a little. Loodis averages it and shows a steady number.
• The surface – a phone is 15 cm long; it can't see a dip in the middle of a long board.

For long floors, kitchen worktops over several metres, door installations or machine setup, use a long spirit level or a laser. For everything around the home – shelves, frames, washing machines, furniture, a camper on a campsite – a calibrated phone is more than enough.