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Flip test — check your phone and find its zero error
How accurate is it? Phone sensors are good to about ±0.5°. A thick case or a camera bump changes the reading, so use the flip test. For a heavy shelf, check with a real level.
About the bubble level
Is the shelf straight? Is the picture hanging level? This bubble level turns your phone into a spirit level. It reads the motion sensor in your phone and moves a bubble, just like the glass tube of a real level.
Open this page on a phone or tablet. Put the phone on the surface, and the bubble shows which side is higher. The page also shows the tilt as a number. Nothing is sent anywhere — the sensor is read on your phone only.
Features
- Three modes — a round bubble for tables and floors, a tube for shelves and picture frames, and an upright mode for walls and door frames
- Angle in your unit — degrees, percent grade, millimetres per metre or inches per foot
- Lock the reading — one big button holds the number so you can lift the phone and read it
- Set zero — make the current position the zero, or reset it at any time
- Flip test — measure, turn the phone 180°, measure again, and find the zero error of your phone
- Green and beep — the screen turns green when you are within 0.1°, with an optional soft beep
- Smooth bubble — the reading is smoothed, so the bubble does not shake
- Full screen — a big view that keeps the screen on while the level is open
How to use it
- Open this page on your phone. On an iPhone, tap Allow motion sensor and say yes
- Choose a mode: Surface, Edge or Upright. The page can suggest the mode from how you hold the phone
- Put the phone on the thing you want to check and wait one second
- Move the thing until the bubble sits in the middle and the screen turns green
- Tap Lock reading to hold the number, then pick the phone up and read it
- Do the flip test once to make sure your phone reads true
The three modes
| Mode | How to hold the phone | What you see |
|---|---|---|
| Surface | Flat, screen up | Round bubble, tilt on two axes |
| Edge | On its long edge | Tube, one angle |
| Upright | Back against the wall | Tube, left-right lean |
Surface is for a table, a floor or a worktop. The bubble moves to the higher side, like in a real round level. Edge is for a shelf or a picture frame: stand the phone on its long edge, with auto-rotate on, so the tube lies flat. Upright is for a door frame or a wall: hold the back of the phone on the wall. The tube shows the lean to the left or right, and a second number shows if the wall leans toward you or away.
Flip test: check your phone
Every phone is a little off. A case, a thick cover or the camera bump can add a small error, and the sensor also has its own. You can find this error with a real surface and a pencil.
- Put the phone on the surface and mark its place. Measure.
- Turn the phone 180° (end for end), back on the same marks. Measure again.
- The surface slope changes sign when you turn the phone, but the error of the phone does not. So the average of the two readings is the zero error.
The page does the maths and shows both numbers. Tap Use as zero to save the correction for this mode. If you also want the real slope of the surface, it is the half of the difference between the two readings.
Degrees, percent, mm/m and in/ft
| Degrees | Percent | mm per m | in per ft |
|---|---|---|---|
| 0.1° | 0.17 % | 1.7 | 0.02 |
| 0.5° | 0.87 % | 8.7 | 0.10 |
| 1° | 1.75 % | 17.5 | 0.21 |
| 2° | 3.5 % | 34.9 | 0.42 |
A drain pipe or a patio often needs about 1 to 2 percent fall. A shelf should be below 0.5°. Use the unit you know best — the page converts for you.
Frequently asked questions
How accurate is a phone level?
About ±0.5° on most phones. After a flip test and with the phone out of its case, you can often get close to ±0.2°. A real spirit level is still better for a heavy shelf, a cabinet or a bench.
Why does the page ask to allow the motion sensor?
On iPhone and iPad, Safari asks before a web page may use the motion sensor. Tap Allow motion sensor and choose Allow. Android phones do not ask. If you said no, allow it in the browser settings for this site and reload.
Why does it say my device has no motion sensor?
Most laptops and desktop computers have no motion sensor, so there is nothing to read. Open the page on a phone or tablet. The page also needs a secure (https) address in most browsers.
Why is the bubble not at zero on a flat table?
Your table may not be flat, or your phone has a small error. Do the flip test. If the phone is the problem, tap Use as zero. If you put the phone in a thick case, take it out for the best result.
Can I use it to hang a picture?
Yes. Stand the phone on its long edge on the top of the frame and use Edge mode. Move the frame until the screen is green.
Does it work offline?
After the page has loaded, yes. The level runs on your phone and sends nothing out.
Good to know
- The bubble moves to the higher side, like a real level
- Turn on auto-rotate on your phone for the Edge mode
- A phone case, a magnet case or a camera bump can change the reading
- The screen stays on while the level is open, if your browser allows it
- Your zero, unit and mode are saved on your device only
Related tools
- Online Protractor — measure an angle on your screen
- Online Ruler — centimetres and inches in true size
- Online Compass — find north with your phone
- Square Footage Calculator — the area of a room
- Tile & Flooring Calculator — how many tiles you need
