How to Shim a Cabinet: Easy Steps for a Perfectly Level Fit

Shimming a cabinet can turn a frustrating installation into a satisfying, professional-looking result. When floors or walls are not perfectly level, cabinets can rock, twist, or sit unevenly. This can cause doors to hang crooked, drawers to stick, and countertops to look off balance.

Yet, with careful shimming, you can create a solid, level base for any cabinet—whether it’s in your kitchen, bathroom, or workshop.

This guide is written for anyone who wants a clear, step-by-step explanation of how to shim a cabinet. You’ll find practical advice, common mistakes to avoid, and useful tips that even some experienced DIYers overlook. By the end, you’ll be ready to handle almost any cabinet installation, even on old or uneven floors.

What Does It Mean To Shim A Cabinet?

Shimming a cabinet means adding thin pieces of material—called shims—under or behind a cabinet to make it level and stable. Most shims are made from wood, plastic, or composite materials. They are usually wedge-shaped so you can adjust the thickness by sliding them in or out.

Why is shimming important? Even in new homes, floors and walls can be out of level by several millimeters. Cabinets need a flat, level base so that doors and drawers work smoothly. Without shimming, you risk gaps, misaligned doors, and wobbly cabinets.

Tools And Materials You Will Need

Before starting, gather the right tools and materials. This will save time and prevent mistakes.

• Shims: Wooden or plastic shims are most common. Buy a pack—you’ll need more than you think.
• Level: A 2-foot or 4-foot spirit level is best. A small torpedo level can help in tight spaces.
• Tape measure: For checking distances and cabinet size.
• Pencil: Mark positions or heights.
• Utility knife or handsaw: To trim shims.
• Hammer or mallet: Sometimes needed to gently tap shims into place.
• Screws and drill: For securing cabinets to the wall.
• Cabinet screws: Special screws that won’t split the cabinet frame.
• Safety glasses: Protect your eyes when trimming shims.

Optional but helpful:

• Laser level: For longer runs of cabinets.
• Construction adhesive: Secures shims to the floor if needed.
• Painter’s tape: Mark positions or protect surfaces.

Some beginners forget the importance of a long spirit level. A short level might show that a small section is flat, but only a longer level reveals if the whole cabinet is truly even.

When And Where To Shim Cabinets

Not every cabinet requires shimming. Here’s how to tell when and where it’s necessary.

• Floors are uneven: Old homes often have sloped or wavy floors. You’ll see gaps under the cabinet base.
• Wall is not flat: Base cabinets may sit away from the wall in spots.
• Corners are out of square: L-shaped or U-shaped layouts may need shims for alignment.
• Tall cabinets rock: If a pantry or tall unit moves when touched, shimming is needed.
• Doors and drawers bind: If they don’t open smoothly after installation, check for unevenness.

Always check the floor and wall before installing any cabinet. Slide the cabinet into position, and use your level to check front-to-back and side-to-side. If the bubble isn’t centered, you’ll need to shim.

Step-by-step Guide: How To Shim A Cabinet

Shimming may sound simple, but the process involves several important steps. Follow this guide for the best results.

1. Prepare The Area

Clear the space where the cabinet will go. Remove old debris, dust, or anything that could interfere with leveling. Place the cabinet in position without fasteners.

2. Check For Level And Plumb

Place your spirit level on top of the cabinet. Check side-to-side (left to right) and front-to-back. Also, check the face of the cabinet with the level vertically (plumb).

If you’re installing wall cabinets, check the wall itself with your level before hanging anything.

3. Identify Low And High Spots

Gently rock the cabinet. If it moves, you have low spots. If you see gaps under the base, these are where shims will go.

Mark the high spots (where the cabinet touches the floor) and low spots (where there are gaps) with a pencil.

4. Insert Shims

Slide shims under the low spots. Do this slowly, one at a time. Keep checking with your level as you go. The goal is to raise the cabinet until it is perfectly level.

For large gaps, you can stack shims together. Alternate the direction of the wedge to create a stable, flat surface.

When shimming along the wall, you may need to add shims behind the cabinet (especially with wall cabinets) so the face lines up with other units.

5. Re-check Level And Adjust

After each shim, re-check with your level. If the bubble moves, adjust by sliding shims in or out. Sometimes, adding shims in one place changes the balance elsewhere.

Don’t rush this step. Patience here pays off with a perfect result.

6. Secure The Cabinet

Once the cabinet is level and does not rock, secure it to the wall studs with cabinet screws. Check level one last time as you tighten the screws—sometimes the cabinet can shift slightly.

If the cabinet moves out of level, loosen the screws and adjust the shims again.

7. Trim Excess Shims

Use a utility knife or small handsaw to cut off the parts of the shims that stick out. Be careful not to damage the cabinet finish.

If you want a very clean look, use a chisel or multi-tool to cut the shims flush.

8. Hide Gaps

If there are visible gaps at the bottom, you can cover them with base molding or a furniture toe kick. For small gaps, paintable caulk can make the installation look seamless.

9. Final Checks

Open and close all doors and drawers. Make sure everything works smoothly. Re-check with the level.

If you see issues, adjust the shims as needed before installing countertops or appliances.

Advanced Tips For A Perfect Cabinet Shim

Some details make a big difference in the final result. Here are insights that many miss:

• Always start at the highest point in the floor when installing a row of cabinets. Shim all other cabinets up to match this height. This prevents a wavy countertop.
• If you’re installing several cabinets in a row, screw them together first before shimming. This keeps faces flush and gaps consistent.
• For heavy cabinets (like pantries), stack multiple shims for stability, and glue them with construction adhesive to prevent shifting.
• Use plastic shims in wet areas (like bathrooms or basements). They won’t rot or absorb water like wood.
• When shimming wall cabinets, check both top and bottom. Shimming only one spot can twist the frame.

Many beginners forget to check the level after securing cabinets. Even a small shift can ruin an otherwise perfect job. Always check before moving to the next step.

Common Mistakes And How To Avoid Them

Even with good instructions, some errors can cause problems. Watch out for these:

• Over-shimming: Adding too many shims can make the cabinet unstable or create a rocking effect.
• Not stacking shims properly: Shims should be stacked in opposite directions to prevent sliding.
• Ignoring wall unevenness: Focusing only on the floor can leave gaps at the back.
• Cutting shims too soon: Always wait until the cabinet is fully secured before trimming shims.
• Using nails instead of screws: Nails can pull loose over time; screws hold better.
• Skipping final checks: Test every door and drawer before calling the job done.
• Not securing shims: Loose shims can shift, causing the cabinet to move later.

A real pro checks their work at every step, not just at the end. If you make a mistake, it’s easier to fix right away.

Choosing The Right Shims: Material Matters

Not all shims are the same. Here’s how different types compare:

Wooden shims are the most common and work well for most situations. For kitchens, they’re usually fine unless you have a history of leaks. In bathrooms or basements, plastic shims are a safer choice.

How To Shim Different Types Of Cabinets

Not all cabinets are the same. Here’s how shimming varies by cabinet type:

Base Cabinets

• Usually need shims under the corners and sometimes in the middle.
• Always check level across the entire length, especially for long runs.

Wall Cabinets

• Sometimes require shims behind the back to keep the face flush with other cabinets.
• Use painter’s tape to hold shims in place while securing.

Tall Or Pantry Cabinets

• Shim all corners and sides for stability.
• Secure to wall studs at multiple points.

Vanity Cabinets

• Use plastic shims to avoid water damage.
• Check that the top is perfectly flat for sinks.

Corner Cabinets

• Shim both the sides and back to get a perfect fit.
• Watch for out-of-square walls.

Example: If you’re installing a 36-inch kitchen base cabinet on a floor that slopes 1/4 inch from left to right, you may need to stack two or three shims at the low end to make the top level. Always secure these shims before adding a countertop.

Credit: www.youtube.com

Using A Laser Level For Large Installations

For larger projects, a laser level can save time and improve accuracy. Set the laser at the height you want for the cabinet tops. Mark this line on the wall. Shim each cabinet so its top matches the laser line. This ensures a perfectly level run, even if the floor varies by several centimeters.

Many beginners skip this step and rely only on spirit levels, which can lead to cumulative errors over a long row of cabinets.

How Shimming Affects Countertop Installation

A properly shimmed cabinet is the foundation for a successful countertop installation. If cabinets are not perfectly level and stable, countertops can crack, warp, or develop gaps.

Installers often use a template to check the flatness of cabinets before setting stone or solid surfaces. If you’re installing laminate or wood countertops yourself, always re-check level after shimming.

If there are gaps larger than 1/4 inch under the countertop, add extra shims and secure them well.

Credit: www.woodmagazine.com

Dealing With Old Or Uneven Floors

Older homes can present unique challenges. Floors may slope, dip, or have high spots. Here’s how to handle these issues:

• Find the highest spot along the cabinet run and start there.
• Shim all other cabinets up to this level. Never try to bring all cabinets down to the lowest point.
• For large dips, consider using a thin plywood subfloor under the cabinets to create a more even surface.

If the floor is extremely uneven (over 1 inch difference), consult a professional. Trying to shim too much can cause instability.

How To Shim Cabinets On Concrete Floors

Concrete can be hard to work with because you can’t nail or screw shims into place. Here’s what to do:

• Use construction adhesive to glue shims to the floor.
• Use plastic shims—they won’t absorb moisture from the concrete.
• Wait until the adhesive cures before loading cabinets with weight.

Concrete floors are common in basements and some modern homes. Proper shimming is essential to prevent cabinet movement over time.

How To Hide Shims For A Professional Finish

Visible shims can spoil the look of a new kitchen or bathroom. Here’s how to cover them:

• Toe kicks: These are strips of material that cover the base of cabinets. Secure them after shimming.
• Baseboard molding: Paint or stain to match cabinets.
• Caulk: For very small gaps.

Some installers paint the ends of shims before installing them, but this is not usually necessary if you use trim pieces.

How Many Shims Do You Need?

The number depends on the length of your cabinet run and the unevenness of your floor.

• For a single 36-inch base cabinet, 4–6 shims are usually enough.
• For a full kitchen, buy a pack of 25–50 shims. You can always use extras for future repairs.

It’s better to have too many shims than to run out halfway through the project.

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When Not To Use Shims

Shims are not always the answer. Sometimes, a floor is so uneven that shimming is not safe or effective. If you need to add more than 1 inch of shims, or if cabinets still feel unstable after shimming, consider:

• Leveling the floor before installation
• Installing a plywood sub-base
• Consulting a professional

Over-shimming can cause long-term problems, including cracks in countertops and loose cabinets.

Real-world Example: Shimming A Kitchen Cabinet

Let’s walk through a real scenario.

You’re installing a 24-inch base cabinet in an old kitchen. When you place the cabinet, the left side is 1/2 inch lower than the right. The back of the cabinet touches the wall, but the front has a gap.

• Place a wood shim under the left front corner and a second shim under the left back corner.
• Check level side-to-side. Add or adjust shims until the bubble is centered.
• Now check front-to-back. If the front is still low, add another shim.
• Once level, secure the cabinet to the wall studs with cabinet screws.
• Trim excess shim with a utility knife.
• Snap on the toe kick to hide the shims.

This process may take 10–15 minutes per cabinet, but creates a professional result.

Cost Of Shimming Cabinets

Shims are inexpensive. A pack of 20 wooden shims costs about $2–$4 USD. Plastic shims cost a bit more, about $5–$8 for a pack of 12.

Labor is the bigger cost. If you hire a pro, shimming and leveling can add $50–$200 to a kitchen installation, depending on difficulty. Doing it yourself saves money and gives you better control over the final result.

Time Needed To Shim Cabinets

For a single cabinet, shimming usually takes 10–20 minutes. For an entire kitchen, plan for 2–3 hours, especially if floors are very uneven.

Don’t rush. The time invested here ensures doors and drawers work smoothly for years.

Tools Comparison: Manual Vs. Laser Level

Which tool should you use for checking level? Here’s a quick comparison:

For most DIYers, a good 4-foot spirit level is enough. For longer installations, renting or borrowing a laser level is worth considering.

Final Quality Check Before Finishing

Before you install countertops, appliances, or plumbing, run through this checklist:

• Check level front-to-back and side-to-side on every cabinet.
• Open and close all doors and drawers.
• Look for visible shims and trim as needed.
• Make sure cabinets are secured to wall studs.
• Ensure toe kicks or base molding cover all gaps.

A few extra minutes here can prevent future problems.

Where To Learn More

For a deeper dive into cabinet installation standards and more advanced techniques, visit the official Wikipedia Cabinetry page.

Frequently Asked Questions

How Thick Should A Cabinet Shim Be?

Most shims are wedge-shaped and range from 1/16 inch to about 3/8 inch thick at the thick end. You can stack them for greater thickness, but avoid going over 1 inch total. Too thick, and the cabinet may become unstable.

Can I Use Cardboard Or Other Materials As Shims?

It’s best to use wood, plastic, or composite shims. Cardboard compresses over time and can lead to loose cabinets. In wet areas, avoid wood and use plastic shims for durability.

Should I Glue Or Screw Shims In Place?

On wood subfloors, you can nail or screw shims if needed. On concrete, use construction adhesive. For most kitchen jobs, simply securing the cabinet with screws is enough to hold shims in place.

Do I Need To Shim Both Base And Wall Cabinets?

Yes, both types may need shimming. Base cabinets often need shims underneath for uneven floors. Wall cabinets may need shims behind the back so their faces are flush and level.

How Do I Know If My Cabinets Are Level After Shimming?

Use a spirit level on the top and front edges. The bubble should be centered. Also, open and close all doors and drawers—they should move smoothly and not swing open or closed by themselves.

Shimming a cabinet isn’t hard, but it does require patience and attention to detail. By following these steps and tips, you’ll create a solid, professional installation that will last for many years.