Installing ready-to-assemble (RTA) cabinets can be a great way to save money on your kitchen remodel. However, because RTA cabinets ship flat-packed, getting them properly aligned and plumbed during installation is critical. If your RTA cabinets end up crooked or out of square, it can ruin the look of your entire kitchen. Fortunately, with some careful planning and the right tools, squaring your RTA cabinets isn’t too difficult. Here’s a step-by-step guide to help you get perfectly aligned cabinets.

Materials Needed

Before starting the installation, make sure you have the necessary supplies:

  • Level – A 4-foot level is best for checking plumb and level across cabinet faces. A small torpedo level will also be useful.
  • Framing square – Essential for checking corners are square.
  • Cabinet clamps – These temporary clamps hold cabinets together while fastening.
  • Shims – Small wooden shims will be used to plumb and level cabinets.
  • Screws – Self-tapping cabinet screws are recommended. Make sure they are the appropriate length.
  • Drill/driver – A cordless drill/driver will make installing screws much easier.
  • Stud finder – Locate studs to secure cabinets to the wall.
  • Laser level (optional) – A laser level projected across the wall is helpful for installation.

Prep the Installation Space

Before installing cabinets, the workspace should be prepped:

  • Remove existing cabinets, countertops, and anything attached to walls.
  • Check walls for level and plumb. Use shims if walls are uneven.
  • Locate and mark stud locations for securing cabinets later.
  • Clean walls and floor thoroughly to create a smooth surface.
  • Have all tools, cabinets, and hardware ready before starting.

Establish Your Base Cabinet Location

The first cabinet installed should be a base cabinet anchored securely to the wall. This will establish the placement for the entire row:

  • Mark a level line on the wall for the top of the base cabinet row. Use a level and measure up from floor 34 1/2″ for standard cabinet height.
  • Place the first base cabinet against the wall aligned with the level line. Check it is also plumb side-to-side using a level.
  • Have someone hold the cabinet in place or temporarily secure with clamps. Make sure the cabinet remains aligned with the level line as you anchor it.
  • Drill pilot holes and use cabinet screws to anchor the cabinet through the back panel into studs. Secure thoroughly to prevent movement.
  • If necessary, use shims between the wall and cabinet to adjust until plumb and level.

Hang Wall Cabinets First

With the first base established, now hang wall cabinets:

  • Measure and mark wall for wall cabinet placement. Make sure they will be aligned with base cabinets below.
  • Drill pilot holes then fasten wall cabinets directly into wall studs with cabinet screws.
  • Have a helper hold cabinets as you anchor them to ensure they remain level.
  • Install filler strips if there are gaps between the wall and cabinet sides.
  • Use a level to double check each cabinet is plumb as you work across the wall.

Connect the Base Cabinets

After anchoring the wall cabinets, move down and install the remaining base cabinets:

  • Place the next base cabinet tight against the first one. The cabinet sides should be flush.
  • Use C-clamps to temporarily hold cabinets together while aligning and fastening.
  • Check the face frame is plumb using a level. Align the fronts perfectly.
  • Drill pilot holes and install cabinet screws through the face frame of the second cabinet into the side of the first. Make sure screws are long enough to secure firmly.
  • Follow this process to install any remaining base cabinets, anchoring them together and checking for plumb as you go.
  • Finally, anchor the entire base row to the wall through the back panels.

Use Cabinet Clamps to Align Corners

Pay special attention when joining two cabinets at a corner:

  • Position corner cabinets tightly together, but do not attach yet.
  • Use two cabinet clamps to pull the cabinet fronts together and hold the corner flush.
  • Check the corner is perfectly square using a framing square. Adjust clamps until the cabinets form a 90° angle.
  • Drill pilot holes and fasten corner cabinets together through face frames while clamps hold alignment.
  • Remove clamps. Corner seam should now remain square on its own.

Check Level Across Cabinets

As you install cabinets:

  • Use a 4-foot level to check level across fronts of base cabinets.
  • Shim under cabinets if necessary to bring tops perfectly level with each other.
  • For wall cabinets, use a level to check undersides are all aligned. Shim if needed.
  • Recheck level and plumb as you go to ensure alignment. Cabinets must be flat and flush.

Scribe Cabinets for an Uneven Wall

If the wall has dips or bumps:

  • Slide cabinet against wall and use a pencil to mark any gaps onto the cabinet side.
  • Remove cabinet and use a jigsaw to cut along the pencil line. This “scribes” the cabinet to match the wall contour.
  • Sand cut edges smooth and reinstall. The cabinet side will now sit flat against the uneven wall.

Shimming Tips for Adjustment

  • Use wedge-shaped wood shims to make small adjustments as needed.
  • Tap shims in between wall and cabinet back to adjust plumb.
  • Insert shims under cabinets to raise and level tops.
  • Only use shims temporarily until fastened – do not leave in place.

Final Checks and Next Steps

Once all cabinets are installed:

  • Recheck every cabinet is level and plumb and securely fastened.
  • Install countertops, adjustable feet, doors/drawers, and hardware per manufacturer instructions.
  • Use silicone caulk to seal around edges and corners.
  • Carefully squared, plumb cabinets will ensure countertops sit perfectly flush.

With attention to detail during the install, your RTA cabinets can look seamlessly custom. Just take your time, use the proper tools, and remember to continually check for level and square. Your new kitchen will come out looking fantastic.

Frequently Asked Questions About Squaring RTA Cabinets

What are the consequences if cabinets are out of square?

Out of square cabinets can cause a variety of issues:

  • Cabinet doors and drawers may not align properly, leaving uneven gaps.
  • Countertops may not sit level, leaving lips or gaps between counters and cabinets.
  • Appliances like sinks may not fit correctly into crooked cabinet openings.
  • Walls, backsplashes, and other finishes may look obviously crooked.
  • The entire kitchen will look sloppy and poorly built.

Should I use the instructions that came with the cabinets?

The included instructions can provide helpful cabinet-specific tips. However, they are rarely comprehensive. Use them for things like door/drawer adjustment but follow the more detailed steps here for the full installation sequence.

What if my floor is uneven?

Check for level across the entire floor where cabinets will sit. If slightly uneven, adjustable cabinet feet can compensate for small discrepancies when installed. But major dips or slopes in the floor must be remedied before installation.

Should I fully install uppers before lowers?

It’s recommended to install at least a few upper wall cabinets first. They will give you reference points for aligning the base cabinets underneath them.

How do I allow room for countertops between stacked cabinets?

When mounting wall cabinets above bases, use spacers to drop them down from the wall the thickness of the planned countertop (usually 1 1/2″) to allow room.

My corner cabinet has a gap, what do I do?

This is common with flat pack cabinets in corners. Use the included corner clamps to pull the cabinet fronts flush until fastened. Check for square with a framing square. Shim internally if a small gap remains.

What is the minimum number of screws to use?

For standard 3/4″ cabinet backs, use at least 6-8 wood screws anchored into studs per base cabinet and 4-6 per wall cabinet for adequate support. Stagger screws to reinforce.


Installing RTA cabinets squares up to a rewarding DIY project that can transform the look a kitchen. While getting everything perfectly aligned takes patience and attention to detail, the right techniques make it very achievable. Starting with a strong base cabinet, double checking for level frequently, using clamps to hold alignment, and making slight adjustments with shims are the keys to success. With some careful planning and elbow grease, you can get professional-looking results from assembled cabinets. Just remember to take your time, follow secure fastening procedures, and keep cabinets square for a kitchen you will enjoy for years to come.