Open the app on your phone to use the level. This page needs a phone’s motion sensor.
How the Bubble Level works
This turns a phone into a level and inclinometer. Lay it flat on a surface to read its tilt (overall, side to side and top to bottom), or stand it on its edge on a pipe or hold its side against a post to check level and plumb. It shows the angle in degrees, the slope in percent and the rise per foot in inches, the way pipe slope is usually given.
The phone's motion sensor measures which way gravity pulls, and the angle comes from that. Slope % = tan(angle) × 100 and rise per foot = tan(angle) × 12". So 1° is a 1.75% slope, and 45° is a 100% slope, 12" of rise per foot.
Example: checking a drain that should fall 1/4" per foot. 0.25 ÷ 12 = 0.0208, so the slope is 2.08% and the angle is arctan(0.0208) = 1.19°. Standing on its edge along the top of the pipe, the phone should read about 1.19°, 2.08% and 1/4" per foot.
Calibrate first: lay the phone on a surface you know is level and tap Calibrate (set zero). It only accepts a zero within 5° of level, so a stray tap can't zero a tilted phone. Check it with the flip test: read, turn the phone end for end on the same spot and read again; the two readings should match. A camera bump makes the phone rock, so set it on a straight board or a level. The reading turns green within 0.2° of level, and Hold freezes it so you can read it after you pull the phone away.
Frequently asked questions
How accurate is a phone level?
Once calibrated, a phone's motion sensor is good enough for most slope and layout checks, but many phones read a little off out of the box, and a case or camera bump adds error. Calibrate on a surface you know is level and confirm with the flip test. When the slope has to pass inspection, confirm it with a good level.
How do I calibrate my phone level?
Lay the phone on a surface you know is level (checked with a good level) and tap Calibrate (set zero); Flat on surface and On edge each keep their own zero. To check it, turn the phone end for end on the same spot: the reading should not change. Reset calibration clears the zero.
What is 1/4 inch per foot in degrees?
1.19°, a 2.08% slope: arctan(0.25 ÷ 12). It is the minimum fall for horizontal drain pipe 2½" and smaller under IPC Table 704.1; 3" to 6" pipe may run at 1/8" per foot (0.60°, 1.04%). Your local code may differ.
How do you convert degrees to percent slope?
Percent slope = tan(angle) × 100. 1° is 1.75%, 5° is 8.75% and 45° is 100%. Degrees and percent are different scales: a 10% slope is only about 5.7°.
How do I check a pipe for plumb with my phone?
Switch to On edge and hold the phone's long side flat against the pipe. The reading is the angle off plumb; at 0° (green) it is plumb. Check from two sides 90° apart, because a riser can be plumb one way and lean the other.