Before using shims, first check if the wobble is caused by loose closet bolts. Locate the two plastic caps on the base of the toilet, one on each side. Carefully pry these caps off using a small flathead screwdriver or a putty knife. Underneath, you will find a nut and a washer on a bolt. Use an adjustable wrench to gently tighten the nut. Alternate between the left and right sides, tightening each one a little at a time to apply even pressure. Tighten them until they are snug, but do not overtighten, as this can easily crack the porcelain toilet base. After snugging them down, try to rock the toilet. If it's still wobbly, proceed to the next step.

With the toilet centered over the floor flange, gently rock it back and forth and side to side to determine where the gaps are between the toilet base and the tile floor. Make a mental note of the locations and approximate size of the gaps. This is where you will insert the shims. For best results, have another person sit on the closed toilet lid to apply weight, which compresses the wax ring and simulates normal use. This ensures you are shimming for the toilet's final seated position.

Take the plastic toilet shims and firmly push them into the gaps you identified. Slide the thin end in first. Add shims around the toilet base as needed until the toilet sits firmly on the floor and does not rock or wobble in any direction. Some shims are designed to be stackable if you have a larger gap. Push them in by hand; you should not need a tool. Be careful not to force them in so hard that you lift the toilet, as this can break the wax ring seal.

Once the toilet is stable and all shims are in place, you need to trim the excess material for a clean look. Take a sharp utility knife and press the blade firmly against the porcelain base of the toilet. Carefully score the shim multiple times where it protrudes. Once scored, you should be able to easily snap off the excess piece by bending it up or down. Be very careful not to let the knife slip and scratch the toilet or the floor.

The final step is to seal the base of the toilet. Load a tube of kitchen and bath caulk or tub and tile sealant into a caulking gun. Cut the tip of the tube at a 45-degree angle to create a small opening. Apply a continuous, even bead of caulk around the perimeter of the toilet base where it meets the floor. This will hide the trimmed shims and prevent water and dirt from getting underneath. Remember to leave a 1-inch gap at the very back of the toilet to allow water to escape in case of a future leak. Use a caulk finishing tool or a wet finger to smooth the bead for a professional-looking finish. Wipe up any excess caulk with a paper towel or rag.