Use a free bubble level app on your phone to check floor level before tiling, installing cabinets, or laying flooring. Step-by-step guide.
An unlevel floor causes cascading problems: doors that won't close properly, cabinets that lean visibly, floor tiles that crack along grout lines, and furniture that rocks. Catching the problem before you start a project saves expensive rework.
Checking a floor with a traditional 4-foot level gives you a point-to-point comparison, but it misses the bigger picture of how the whole room slopes. A phone app lets you check quickly at multiple points and build a mental map of where the high and low spots are.
Open
Before checking your floor, calibrate the app: set your phone on a surface you know is level (like a granite kitchen countertop that was professionally installed), and use the 180° calibration tool in the app. This removes any factory offset from your phone's accelerometer and ensures accurate readings. Save the calibration profile so it persists between sessions.
Place your phone flat on the floor in the center of the room. The bullseye indicator shows any cross-slope. Note whether the bubble is centered or which direction it drifts. A drift of more than 0.5° is usually noticeable once tile or a floating floor is installed.
Walk the perimeter, placing your phone every 3–4 feet along each wall. In horizontal level mode, this tells you whether the floor slopes toward or away from that wall. Make a quick note of the readings — even a rough sketch on paper helps.
Check corner-to-corner diagonally. This reveals if one corner is significantly higher or lower than the rest, which would indicate a hump or depression that's less obvious from wall-to-wall measurements.
Check floor-to-floor transitions between rooms and at doorways — these spots accumulate measurement error if multiple trades worked the subfloor at different times.
Industry tolerances for residential floors vary by flooring type:
Bubble Level & Angle Gauge shows readings in degrees, percent slope, and mm/m. Convert by remembering that 0.1° over 3 meters is approximately 5mm of drop — or use the percent reading directly: 1% slope = 10mm per meter.
Minor variations (under 3/16 inch over 10 feet) are common in residential construction and can usually be accommodated with a self-leveling compound applied before flooring installation. For larger deviations, a flooring contractor or general contractor should assess whether the issue is in the subfloor or the structure below.
If you're checking before buying furniture, remember that most furniture can be shimmed under legs to compensate for floor slope — you don't need a perfectly level floor to have stable furniture.
For a whole-home survey before a renovation, create a simple grid and record the angle at each measurement point. The hold feature in Bubble Level & Angle Gauge lets you lock the reading and move to a notepad without disturbing the phone's position — useful for single-person surveys across multiple rooms.
A phone app measures the angle of the surface you place it on. Loose or warped subfloor panels can give inconsistent readings as the panel flexes under the phone's weight. For a professional pre-tile assessment, a floor flattening check requires a long straightedge or a laser level to catch small, localized high spots. Phone apps are excellent for identifying macro-level slope issues; they're less suited to detecting small, localized humps.
Bubble Level & Angle Gauge is free for