How to use your phone as an angle finder
- Open this page on your phone (iPhone or Android). On iPhone, tap Tap to enable motion sensor and allow access.
- Zero it (optional but recommended). Put the phone on a surface you know is level, such as a table checked with a spirit level, and tap Zero. This cancels out any tilt caused by your phone case or camera bump.
- Choose a position. Flat on surface if the phone lies on its back. Edge against surface if you hold the long edge of the phone against something with the screen facing you.
- Place the phone and read the angle. Wait a second for the number to settle, or tap Hold to freeze the reading so you can pick the phone up and read it.
- Need the angle from vertical? Switch Measure to From vertical to check plumb (for posts, door jambs and walls).
Accuracy tips
- Remove a bulky or uneven case, or at least zero the app with the case on. A thick camera bump can add 1° or more.
- Keep still. The sensor reads gravity, so any movement adds noise. Turn smoothing to High for steady readings on a vibrating surface.
- Measure twice, flipped. Take a reading, rotate the phone 180° on the same spot and read again. The average of the two cancels most sensor bias.
- Use the long edge in edge mode. It bridges small bumps and gives a more representative reading than the short edge.
What you can measure with a phone angle finder
| Job | Typical angle | How to measure |
|---|---|---|
| Table saw / miter saw bevel | 45°, 22.5°, 90° | Zero on the saw table, then lay the phone against the blade (edge mode). |
| Stairs | 30°–37° | Lay the phone on the stringer or the handrail (flat mode). |
| Wheelchair ramp | ≤ 4.76° (1:12 slope) | Flat on the ramp surface. The ADA maximum running slope is 1:12, about 4.8°. |
| Roof pitch | 4/12 to 12/12 (18°–45°) | Flat on a rafter or on the roof deck. The pitch is shown in x/12. |
| Drainage / patio slope | 1/4 in per ft (≈1.2°, 2%) | Flat on a straight board laid across the surface. |
| Hanging pictures & shelves | 0° | Edge mode against the top of the frame or shelf. |
How it works
Every smartphone contains an accelerometer that senses the direction of gravity. Your browser turns those readings into two tilt angles (called beta and gamma). This page combines them into a single gravity direction, then calculates how far your phone's screen (flat mode) or long edge (edge mode) is tipped away from level. A smoothing filter averages out hand tremor and sensor noise. The whole calculation happens on your phone; nothing is sent to a server.
No sensor on your device? Measure on screen with the online protractor, or take a picture and use measure angle from photo.
Frequently asked questions
How accurate is a phone angle finder?
Most modern phones measure tilt to within about ±0.1° to ±0.5° when the phone is still. Accuracy suffers if the phone case is uneven, the camera bump rocks on the surface, or the phone is moving. Use Zero on a known level surface first, then measure, and turn smoothing up for a steadier reading.
Why does my iPhone ask for permission to use motion?
Since iOS 13, Safari asks before a website can read the motion sensor. Tap "Tap to enable motion sensor" and then "Allow". Nothing is recorded or sent anywhere; the readings are only used on this page.
Can I use the angle finder on a laptop or desktop?
Only if the device has a motion sensor, which most laptops and desktop computers do not. On a computer, use the online protractor to measure angles on your screen, or measure an angle from a photo.
What is the difference between "flat" and "edge" mode?
Flat mode is for laying the phone on its back on a surface (a board, a table, a saw blade laid flat) and measures how much that surface tilts. Edge mode is for holding the long edge of the phone against something (a door frame, a rafter, a stair stringer) with the screen facing you, like a spirit level.
How do I convert the angle to roof pitch?
The angle finder shows the pitch automatically as rise per 12 inches of run. For example 26.6° is a 6/12 pitch. You can also use the roof pitch to degrees calculator.
Does the angle finder work offline?
Yes. After you have opened it once, the angle finder works without an internet connection, which is handy on a job site.