How to Level Base Cabinets on Uneven Floors: Shims, Legs and Countertop Tolerances

If you want to know how to level base cabinets, the short version is this: find the highest spot of floor under the whole run, mark a level line 34-1/2 inches above it, set every cabinet top to that line, and fill the space under the lower boxes with shims placed under the cabinet sides, never in the middle of an unsupported bottom. You work up from the high point because a cabinet can be raised with a shim but it cannot be pushed into the floor. The rest of this page is the detail that decides whether a stone countertop sits flat on those boxes or cracks six months later.

We sell cabinets and ship them nationwide, but we do not install the cabinets you buy from us. This is the method we would want your installer, or you, to follow before a fabricator comes to template. We build and remodel kitchens ourselves, and the calls we get after delivery are rarely about a bad box. They are about a floor that dropped half an inch toward the back door and nobody measured it until the countertop was on the truck.

Key Takeaways

• Start at the high point: survey the floor along every wall and the island footprint, then set the 34-1/2" top line from the highest reading. Every other cabinet comes up to meet it.
• Shim under the sides: the load in a base cabinet runs down the side panels and the toe kick. Shims go under the sides at the front and back and under the kick where it meets a side.
• The countertop maker sets the tolerance: Cambria's guideline says the support must not be out of plane more than 1/8" per 8 feet; Caesarstone's guide specification asks installers to verify substrates are plumb, level and flat within 1/16" in ten feet.
• Your line decides shims or legs: Fabuwood Allure has an attached 3/4" plywood toe kick you shim under; Fabuwood Illume and St. Martin Vista sit on adjustable leveling legs.
• Protect the dishwasher bay: the Bosch SHE3AR75UC needs a 33-7/8" tall cutout. Set cabinets on the subfloor and add tile afterward, and that opening can end up too short.

Table of Contents

• How Level Is Level Enough for a Countertop?
• Finding the Floor's High Point
• Marking the 34-1/2" Line
• Shims for Cabinets: Composite, Wood and Horseshoe
• Where the Shims Go: Sides, Toe Kick and Back
• Setting the Run One Box at a Time
• Screwing to Studs Without Pulling It Out of Level
• Adjustable Leveling Legs: Which Lines Have Them
• Hiding the Gap at the Floor
• Leveling an Island on Floor Cleats
• Sink Bases and the Dishwasher Opening
• Concrete, Tile, Hardwood and Floating Floors
• Worked Example: A 10-Foot Run on a Sloping Floor
• Mistakes That Show Up at Countertop Day
• Frequently Asked Questions

How Level Is Level Enough for a Countertop?

A fabricator checks two things. Level: the tops are horizontal end to end and front to back. Flat, or in plane: every box top sits at the same height as its neighbor, with no bump at a seam. A run can be dead level at both ends and still carry a 3/16" hump where one box was set proud, and a quartz slab rocks on it.

You do not have to guess the number, because the countertop makers publish it. Cambria's countertop installation technical guideline says "the support structure must not be out of plane more than 1/8" for every 8' length" and must "provide support without deflection." That is a flatness rule for the cabinet tops, not a level rule. Caesarstone's architectural guide specification, the template architects drop into project specs, is tighter and covers both: before installing, the installer is to "verify that substrates supporting quartz surfaces are plumb, level, and flat to within 1/16 inch in ten feet." Caesarstone also lists uneven or unstable cabinets among the common causes of cracks after installation.

Our working target under stone: within 1/16" of level across any single cabinet, the whole run within 1/8" end to end, and no step at any seam you can feel with a fingertip. Ask your fabricator what they accept before you start, because they are the ones who will turn the truck around. Our guide to countertop types, heights and depths covers slab thickness and the 36" finished height these numbers are built around.

Finding the Floor's High Point

Almost no kitchen floor is flat. Joists crown and sag, slabs are poured with a pitch, and old houses settle toward the middle. The high point, the spot under the cabinet footprint where the floor sits highest, sets the height of every box in the room. Find it with a self-leveling laser or a 6- to 8-foot level on a straight board; the full tool and screw list is in our step-by-step on how to install kitchen cabinets yourself.

Set the laser so its line crosses every wall that gets base cabinets. Work along each wall with a tape, measuring from the floor up to the line at the wall and again about 22 inches out, where the cabinet front will land. Take a reading every 12 to 24 inches and at anything that looks like a change: a threshold, a sistered joist, a seam between old and new subfloor. Pencil the numbers on the wall.

The smallest number is the high point, because that is where the floor comes closest to the line. Circle it. Measure the island footprint from the same laser setup, because an island set level with itself but 1/4" higher than the perimeter is obvious the day the tops go on.

Two details change where you measure. Measure the floor the cabinets will actually sit on; if they go down before tile or hardwood, survey the subfloor and plan the finished floor thickness separately (see floor types). And take both readings, wall and front, at each spot. A floor can be level along the wall and fall 3/8" toward the room, which shows up as a cabinet that tips forward.

Marking the 34-1/2" Line

Standard base cabinets are 34-1/2" tall, which with a countertop of about 1-1/2" puts the work surface at 36". The Fabuwood Allure spec book lists its standard bases at 34-1/2", the same height used across the industry. Measure 34-1/2" up from the circled high point and mark it. That mark is the top of every base cabinet in the room.

Carry it around every base wall with the laser and draw the level line, then mark every stud along it. If wall cabinets go up first, the same high point sets their line too; our article on how to hang upper kitchen cabinets covers that side.

Now measure from the line down to the floor at every cabinet position. Whatever the reading is over 34-1/2" is the shim stack that box needs; write it on the wall. If any number comes out past about 3/4", stop and look at the floor before you plan a taller pile of shims. Check it against anything fixed, like a window stool or the drain stub-out, while a conflict is still pencil on drywall.

Shims for Cabinets: Composite, Wood and Horseshoe

A shim is a thin wedge or plate that takes up a gap under or behind a cabinet (our glossary entry on shims has the short definition). Three kinds are worth keeping on hand.

Tapered shims always go in pairs, thick end to thin end, so the top and bottom faces stay parallel. A single wedge gives the cabinet a sloped bearing point that touches on one edge. Slide the pair together until the box comes up to the line.

We use composite under anything near water. A cedar shim under a sink base that sees one slow drip turns soft, and a soft shim under the heaviest part of the countertop becomes the low spot you find when the seam opens.

Where the Shims Go: Sides, Toe Kick and Back

Follow the weight. A countertop, a sink full of water and a person leaning on the edge all push straight down through the side panels. On a framed base, the sides reach the floor directly or through the toe kick board, and the bottom deck hangs between them. So the shim goes under the side, not under the bottom.

• Front corners: a shim under the toe kick right where it meets a side, or under the side just behind the kick. This is where most of the lift happens on a floor that falls toward the room.
• Back corners: a shim under the side near the wall, slid in from the open side before the next box goes in.
• Middle of a wide box: under a 36" sink base or a wide drawer base, add a shim under the toe kick at the center if the floor dips there, so the kick does not flex.
• At every stud: a shim pair between the back rail and the wall wherever a screw goes into the stud, so the screw pulls against something solid.

Do not shim only under the middle of the cabinet bottom. It lifts the box, but now a 1/2" or 5/8" bottom panel carries a load it was never meant to, and the box can rack when the top goes on. A shim under the front of the kick with nothing at the back is the same mistake in another direction: the box tips forward and the countertop overhang wanders along the run. On lines with a recessed plywood base, frameless or not, you shim the same way. On lines with legs, you turn the legs instead (see below). Our guide to the parts of a kitchen cabinet names each panel if the terms are new.

Setting the Run One Box at a Time

Start with the cabinet at the high point, or with the corner cabinet if the high point is close to it. A corner base ties two walls together, so setting it first gives both runs a true start. If the high point is mid-wall and far from any corner, start there and work out both ways.

Set the first box on its line and check it three ways: side to side across the top, front to back on both sides, and plumb on the face. Shim until all three read true, then fasten it loosely at one stud so it cannot move while you set the next. Each box after that gets shimmed to the line and clamped to its neighbor so the faces and tops are flush before the two are screwed together. The joining hardware and sequence for framed and frameless boxes are in the install guide's fastening section.

The habit that separates a flat run from a lumpy one: lay a 6- or 8-foot straightedge across three box tops at a time as you go. A single box can be dead level and still sit 1/16" higher than the one beside it. Three of those in a row is a hump a quartz slab will rock on, and a 2-foot level on one box will never show it.

Keep the run straight to a string or laser along the front and let the gap behind be whatever the wall gives you, filled with shims at the studs. Pulling a box into a hollow racks it and the doors stop lining up. The ends get a filler or scribe molding, planned in the order; see end panels, scribe molding and fillers.

Screwing to Studs Without Pulling It Out of Level

This is where good leveling gets undone. You shim a box perfectly, drive a screw through the back rail into a stud, and the screw draws the top of the box toward the wall. The level you just set is gone, and the front edge of the top has lifted.

Prevent it with the order of operations. Level the box. Slide a pair of shims behind the back rail at each stud, snug but not forced. Drive the screw through the rail and the shims into the stud and stop when the head seats, so it clamps the rail against something solid instead of pulling it across a gap. Check the level after every screw; it takes seconds. Use washer-head cabinet screws, not drywall screws; the install guide lists the screw sizes the manufacturers specify. Snap the shims off flush once everything is tight.

Find the supply lines, drain and cables behind a sink base or range before you drill. Gas, electrical and plumbing hookups are licensed work in most places; set the boxes and leave the connections to the trades your local code requires.

Adjustable Leveling Legs: Which Lines Have Them

Leveling legs are plastic feet that screw up and down under the corners of a base cabinet, with the toe kick clipped on after the run is level. You turn a foot instead of stacking shims, each corner adjusts on its own, and the box stays off the floor, away from a small spill. The catch is range: legs take out ordinary variation, not a floor that falls an inch across the room, so compare your high-point readings with the travel. Here is what the manufacturers' own documents say about the base on the lines we sell.

Illume's spec book notes its listed heights are before the feet go on, so set the feet to your 34-1/2" line like any other base. For the frameless lines not listed (Modernform's European series, NOMA, USCD Palermo and Torino) the documents we hold do not spell out the base, so we will confirm it for your order rather than guess. Our comparison of Fabuwood Illume vs Ovela shows the same door on both kinds of base, the Illume review covers the rest of that line, and our St. Martin review covers Vista.

Hiding the Gap at the Floor

Every shim leaves a gap under the toe kick. On most floors the cover hides it; on a floor that falls 3/8" or more along a run, it shows as a dark wedge. Deal with it by size. Under about 1/4", set the cover down onto the floor and let its top edge tuck up under the box; nobody sees the top of a toe kick. From about 1/4" to 1/2", add scribe molding or quarter round at the floor line in the cabinet finish. Beyond that, rip a wider kick and scribe it to the floor, or fix the floor before the cabinets go in.

These parts are cheap next to the cabinets. In the twelve Fabuwood Galaxy finishes that share one price list (the new Macadamia Beige has the TK8 and SM8-S at the same prices, but not the TK8-3/4 or QRM yet), an 8-foot TK8 toe kick cover is $55.90, the 3/4" TK8-3/4 is $58.50, SM8-S scribe molding is $39.00 per 8-foot length and QRM quarter round is $62.40. Order a stick more than your measurement says, because returns at exposed ends eat length. The full range is on our decorative accessories page, and the skin panels and gables guide covers the exposed ends where a toe kick turns a corner.

Put the toe kick on last, after the top and appliances are in, so you can still reach a shim.

Leveling an Island on Floor Cleats

An island has no wall, so it anchors to 2x4 cleats screwed to the floor inside the footprint, set in so the cabinets' kicks and sides drop over them. The leveling happens before the cleats are fastened. Lay out the footprint from the same laser line as the perimeter, find the island's own high point, and shim the cleats level with each other and across the island. Screw them down, set the cabinets over them, shim the boxes to the island's 34-1/2" line, and fasten into the cleats. Island and perimeter now share one reference.

Know what is under the floor before you drive a screw: radiant tubing, a gas line or a duct can sit right where a cleat goes, and a slab needs masonry anchors. Confirm the aisles first too; our kitchen island clearance guide has the widths.

Sink Bases and the Dishwasher Opening

The sink base carries more than any other cabinet: the sink, a basin of water, a disposer, and a stone top weakened by a large cutout right above it. Cambria's guideline calls for support within 3" of any cutout. Shim all four corners of the sink base, with composite. Our sink base cabinet guide covers sizes and the plumbing cutouts in the back.

The dishwasher opening is where leveling mistakes cost the most, because the appliance has a fixed minimum. The Bosch SHE3AR75UC spec sheet, for example, lists a required cutout of 33-7/8" x 24" x 24" and tells you to check the installation instructions before cutting; other brands publish their own. The height runs from the finished floor in the bay to the underside of the countertop.

The cabinets either side must be at the same height and parallel, and the opening 24" wide top and bottom. Then the floor, which is the one people miss. Set the cabinets on the subfloor with the bay at the high point, then lay 3/4" of tile, backer and thinset, and the opening shrinks from 34-1/2" to 33-3/4", which is 1/8" short of that Bosch. Either run the finished floor into the bay before the cabinets go in, or add its thickness to your line.

A return panel next to the opening keeps a finished face beside the appliance; Fabuwood Allure's spec book lists DWR panels 34-1/2" tall in 1-1/2", 3" and 6" widths. Our kitchen dimensions guide lists the other appliance openings to check before you order.

Concrete, Tile, Hardwood and Floating Floors

The floor type changes how you level and whether the cabinets go down before or after the finished floor.

A click-lock floor moves as one sheet, and a row of loaded cabinets pins it. Pergo's Pergo Extreme installation instructions put it plainly: "Kitchen cabinets must be installed before the floor is installed. Do not install cabinets on top of Pergo Extreme flooring." Other products word it differently, so read the instructions for the floor you bought; they decide whether its warranty still applies.

Worked Example: A 10-Foot Run on a Sloping Floor

This is the kind of floor we see in older houses. A 10-foot wall gets, left to right, a 24" base, a 36" sink base, a 24" dishwasher opening and a 36" drawer base. The laser is set at any convenient height, and the installer reads floor-to-laser every 2 feet along the cabinet front line.

The smallest reading, 40-1/8" at 4 feet, is the high point. The cabinet tops go 34-1/2" above it, which is 5-5/8" below the laser (40-1/8" minus 34-1/2"). The installer marks that line and sets the sink base first, since it sits on the high point.

The floor is 1/8" low at the left, peaks at 4 feet and falls 1/2" by the right wall, so boxes set straight onto it would be far outside Cambria's 1/8"-per-8-feet flatness limit. Shimmed to the line, every top lands in one plane.

Now the dishwasher. Its bay runs from about 1/16" below the high point at the 5-foot mark to about 3/16" below at 7 feet, so on the subfloor the opening is roughly 34-9/16" to 34-11/16" tall, with plenty of room for a 33-7/8" cutout. Add 3/4" of tile afterward and the tight end drops to about 33-13/16", 1/16" short. That is why the tile goes into the bay first on this job, or its thickness goes into the line.

Finally the trim. Under the left 5 feet the gap never passes 1/8", so a toe kick cover set on the floor hides it. Under the drawer base it grows from about 3/16" to 1/2", so that 3-foot stretch gets a cover plus scribe molding. Five feet and three feet of kick is exactly one 8-foot stick with nothing spare, so buy two. In a Galaxy finish that is two TK8 covers at $55.90 and one SM8-S at $39.00, $150.80 for the floor line on this wall.

Had the right end read a full inch low, we would look under the floor before ordering trim. An inch over 6 feet usually means a sagging joist or an old repair, cheaper to fix now than to hide later.

Mistakes That Show Up at Countertop Day

• Starting before the survey. The first box goes in the corner, then the high point turns up three cabinets later. Every box already set is too low, and the fix is to pull them.
• Leveling the island on its own bubble. Level with itself, but not with the perimeter line, so it ends up at a different height from the counter facing it.
• Trusting yesterday's floor. A fresh subfloor patch or leveling compound that was still curing can move. Survey on the day you set the cabinets.

Handing it to a pro? Our guide to cabinet installation cost and labor covers how installers price the work, and contractors can look at our Captivating Pro trade program. For which bases to order, see base cabinet types and sizes and framed vs frameless cabinets, which often decides shims or legs.

Frequently Asked Questions

Do base cabinets have to be perfectly level?

Not perfectly, but close. Under stone, aim for no more than 1/16" across any cabinet and 1/8" over the run, with flush seams. Cambria's guideline allows the support 1/8" out of plane per 8 feet, and Caesarstone's guide specification asks for plumb, level and flat within 1/16" in 10 feet. Laminate is more forgiving, but a dip still shows at the backsplash.

What shims should I use for kitchen cabinets?

Composite under the cabinets, especially the sink base and beside the dishwasher, because they do not compress or rot. Wood is fine behind the cabinets at the studs.

Do you shim under the toe kick or under the cabinet box?

Both, at the right spots: under the sides at front and back, and under the kick where it meets a side. Never only under the middle of the bottom panel.

How much can you shim a base cabinet?

Up to about 1/2", a stack stays stable and the gap is easy to trim out. Past 3/4", look at the floor first; the kick gap gets hard to hide and a tall stack can shift.

Which is easier to level, legs or shims?

Legs, on a normal floor: you turn each foot and clip the kick on afterward. Fabuwood Illume and St. Martin Vista use legs; Fabuwood Allure has an attached plywood toe kick that you shim. Both give a level top when done carefully.

Do you install cabinets before or after flooring?

It depends on the floor. Floating floors go in after, around the cabinets. Tile and nail-down hardwood can go either way, but if the cabinets go down first, the finished floor still has to run into the dishwasher and range bays or those openings end up short.

Get the Cabinets Right Before the Floor Gets a Vote

Most leveling trouble can be seen on paper before the cabinets ship: a dishwasher bay on the low end of a sloped floor, a wall that needs a scribe filler, an island that has to line up with a range. Send your measurements and floor readings with your order and we will flag them. Our design service returns a 3D layout and an itemized quote within 24–48 hours.

Reach us through our contact page or call 609-900-3358. Tell us which line you are looking at and we will confirm its base detail, legs or toe kick, so your installer knows what is coming before the pallet arrives.