Why Shelves Go Crooked

Most crooked shelves aren't the result of bad brackets or bad walls — they're the result of skipping the level check. It takes 30 seconds to verify level before you drill, and fixing a crooked shelf after the fact requires patching holes and starting over. The math is obvious: check first.

This guide walks through a complete floating shelf installation using Bubble Level & Angle Gauge — the free phone app that replaces your spirit level for this task.

Tools You Need

  • Smartphone with Bubble Level & Angle Gauge (iOS) or Android version
  • Drill and appropriate drill bits
  • Shelf brackets or French cleat
  • Pencil and tape measure
  • Wall anchors or screws (for stud mounting)
  • Stud finder (optional — you can use magnetic stud detection through another app)

Step 1: Choose Your Height and Mark the First Bracket

Decide where you want the shelf and mark the left edge bracket position. Use the tape measure to position it at the right height from the floor or from an adjacent shelf. Mark the bracket hole positions with a pencil.

Step 2: Find the Level for the Second Bracket

This is where most people go wrong: they measure from the floor to position the second bracket, assuming the floor is level. Floors are rarely perfectly level.

Instead, open Bubble Level & Angle Gauge and switch to horizontal level mode. Hold a long straight board (or the shelf itself) against the wall, resting on the already-marked first bracket position. Hold your phone flat on top of the board. The bubble shows you in real time whether the board is level.

Adjust the right end up or down until the reading says OK and the bubble is centered. Then mark where the right bracket needs to go.

Using the Hold Feature

Once you've found level, tap the hold button in the app to lock the reading. Now you can move the phone away from the board and still see the measurement. This is useful when you need to look at your pencil while keeping the board in place with your other hand.

Step 3: Check the Bracket for Plumb

After marking bracket positions, switch to vertical plumb mode in the app. Hold the phone vertically against the bracket mounting area. Confirm the wall is plumb (perfectly vertical) at that location — rare but possible to have a slightly leaning wall, especially in older construction.

If the wall leans more than 1°, account for this when you install the bracket so the shelf itself reads level regardless of what the wall is doing.

Step 4: Drill and Mount Brackets

Drill at your marked positions. Install brackets per their instructions. Before tightening fully, place the shelf board on the brackets and check level once more with your phone on top of the shelf. Minor adjustments are easier to make before the screws are fully tightened.

Step 5: Final Verification

With the shelf fully installed and tightened, set your phone on the shelf surface and take a final reading. This catches any flex in the brackets or slight slope in the shelf board itself. If the reading is off by more than 0.5°, you can usually correct it by loosening one bracket and shimming with a thin washer.

Floating Shelves vs Bracket-Mounted Shelves

The process is the same for floating shelves (hidden bracket or French cleat) with one difference: your reference line matters more because you can't make micro-adjustments after the sleeve is in the wall. Take extra care on the level verification step before drilling the second set of holes.

Tips for Multiple Shelves

When installing a vertical run of shelves (like a bookcase wall), use the app's angle measurement mode to verify equal spacing. Measure the angle from the bottom of one shelf to the top of the next. Consistent angles mean consistent visual spacing, which makes the installation look professionally done.

For an alcove with shelves on both sides, use the bullseye mode to verify that opposite shelves are at exactly the same height — place your phone on one, note the exact reading, then check the other.

Download and Start Your Next Shelf Project

Get Bubble Level & Angle Gauge free on iPhone or Android. No ads, no account, works completely offline. Your shelves will be level the first time — every time.