Bubble Level
A free bubble level online that turns your phone into a spirit level. Lay it flat to level a table, or stand it on its edge to check a shelf or a picture frame.
Lay the phone flat on the surface
How This Bubble Level Online Works
This bubble level online is a digital level: it reads your phone's tilt sensor through the browser and moves the bubble the way the air bubble in a spirit level moves: toward the high side. Lay the phone flat and you get a round bullseye level with a left–right and a front–back reading. Stand it on a long or short edge and it switches to a tube level for shelves, door frames and pictures. It does the job of a spirit level app on Android or iPhone, but nothing is installed and no reading ever leaves your phone. Updated 2026-09-26.
The big number is the tilt in degrees. The slope shows the same angle as a percent grade and as inches of rise per foot (or millimetres per metre), which is how builders, deck installers and plumbers usually talk about fall. When the reading is within 0.2° the bubble turns bright and the label says LEVEL.
Make Your Phone Level Accurate: the Flip Test
A phone is not a machined straightedge. A case, a camera bump or a slightly bent frame makes it read a small angle on a perfectly flat table. Carpenters remove that error with the flip test, and the Flip calibration button does it for you:
- Put the phone on the surface and tap Flip calibration.
- Turn the phone 180° in the same spot and tap it again.
- The two readings are averaged. What is left over is the phone's own bias, and it is subtracted from every reading after that.
If you already have a surface you trust, Calibrate here sets it as zero in one tap. Calibration is saved on this phone, so you only do it once. For structural work, confirm with a real spirit level.
Degrees, Percent Slope and Inches per Foot
The same slope can be written three ways. The conversion is exact: percent = tan(angle) × 100, inches per foot = tan(angle) × 12, and millimetres per metre = tan(angle) × 1000.
| Inches per foot | Percent | Degrees | mm per metre |
|---|---|---|---|
| 1/16 in | 0.52% | 0.30° | 5.2 mm |
| 1/8 in | 1.04% | 0.60° | 10.4 mm |
| 1/4 in | 2.08% | 1.19° | 20.8 mm |
| 1/2 in | 4.17% | 2.39° | 41.7 mm |
| 1 in | 8.33% | 4.76° | 83.3 mm |
| 2 in | 16.67% | 9.46° | 166.7 mm |
Bubble Level Uses Around the Home
Flat mode is the quick check for a table, a washing machine, a fridge, a bed frame or a camera tripod. Edge mode is for anything vertical or narrow: hang a picture by resting the phone on the top of the frame, check a shelf before you drill the second hole, or hold the phone against a door frame to see whether it is plumb. Use Hold reading when you cannot see the screen, such as a level on a high shelf, then read it after you lift the phone down.
Frequently Asked Questions
How accurate is a bubble level on a phone?
It is as accurate as your phone's tilt sensor and how flat the phone sits. A case or a camera bump adds a small, constant error, which the Flip calibration button removes: measure, turn the phone 180 degrees, measure again, and the bias is averaged out. For hanging pictures and levelling furniture a calibrated phone is plenty; for structural work, confirm with a real spirit level.
Why does the level not read zero on a flat table?
Usually the phone itself is not flat against the table: a camera bump, a case edge or a curved back tilts it slightly. Use Flip calibration on that table and the reading will settle at zero. The calibration is stored on this phone, so you only need to do it once.
How do I use it on an iPhone?
Safari asks for permission before a web page can read motion sensors. Tap Start level and choose Allow. If you tapped Don't Allow, reload the page to be asked again.
Is this a level app? Do I need to install one?
No install is needed. It works like a bubble level app on Android and iPhone but runs in your browser. To open it like an app, use your browser menu and choose Add to Home screen.
Does this bubble level work on a laptop or desktop?
Almost no laptop or desktop computer has a tilt sensor, and a browser cannot invent one, so the page says so instead of showing a fake bubble. Open the same address on your phone or tablet.
How do I check if a shelf or picture frame is level?
Stand the phone on its long edge on top of the shelf or frame. The page switches to a tube level automatically. Adjust until the bubble sits between the two lines and the label says LEVEL. Use Hold reading if the spot is too high to see the screen.
What is the difference between degrees and percent slope?
Degrees measure the angle itself. Percent slope is how much the surface rises for every 100 units of length, which equals tan(angle) x 100. A 1/4 inch per foot fall is about 2.08 percent or 1.19 degrees. The page shows degrees, percent and inches per foot (or mm per metre) at the same time.
Does the bubble level work offline and is it private?
Yes. Once the page has loaded it needs no connection, and the sensor readings are processed only in your browser. Nothing is uploaded or stored anywhere except your own calibration, which stays on this phone.