"Uneven floor" is the diagnosis buyers reach for whenever furniture will not sit still, and it is wrong often enough to matter. Of the four conditions that make furniture rock, adjustable feet can correct two. On the other two, buying longer-threaded levellers makes the problem worse, because the actual fault is in the furniture or in the structure of the floor.
The distinction is worth getting right before spending anything. A cabinet resting on a twisted carcass will still be untwisted by nothing you attach to its base — the base feet will simply transfer the twist to the door line, where it becomes visible as misaligned doors. A cabinet on a floor that deflects under load will be level when it is installed and level no longer once it is loaded. Both cases arrive at the same symptom, and neither is a foot problem.
This guide sets out how to tell the four causes apart, what each one requires, and then how to size an adjustment range properly when feet are the right answer — including the tolerance stack that most specifications omit. It draws on 15 years of manufacturing adjustable feet and levellers for furniture producers across 40+ countries.
Adjustable feet, levellers, and connecting levellers
The Four Causes of a Rocking Furniture
The symptom is identical in all four cases: the item does not sit on all its supports. The causes are not.
| Cause | How it presents | Test | Adjustable feet the answer? |
| Floor slope | A consistent fall along the run; the same end is always low | Level across the full run, not at one point | Yes |
| Floor surface irregularity | Rocks at one spot only; the wobble moves if the unit is turned | Straightedge under each support position | Yes, with a larger or compliant base |
| Carcass twist or an out-of-flat base | Rocks even on a known-flat floor | Stand it on a flat reference surface | No — the carcass must be re-squared |
| Floor deflection under load | Level when empty; sags or rocks once loaded | Load it and re-check the level | No — the floor must be stiffened |
| Measurement error | The floor "measured uneven" at the wrong time or place | Re-measure in place, loaded, at the support positions | Not applicable |
The Diagnostic That Separates Them in Ten Seconds
Before measuring anything, count how many supports are touching and which ones.
Three touching, one lifted. This is a local deviation or a slope. One corner of the floor is lower than the plane the other three define. This is the case adjustable feet are built for — the lift is a single-point correction.
Two touching, and they are diagonal. The unit is see-sawing across one diagonal. This is a twist, and a twist is not a slope. Either the floor is warped or the carcass is, and leveling the four feet will not remove it — it will convert an obvious rock into a hidden distortion that loads two feet and unloads the other two, which is worse for the furniture and invisible to the customer until a door stops closing.
The test that decides which: put the unit on a surface you know is flat — a granite slab, a machine bed, a large sheet of glass on a verified surface. If it still seesaws diagonally there, the carcass is twisted and the floor is innocent. If it sits perfectly, the floor is the problem.
Why the Twist Case Gets Misdiagnosed
A twisted carcass is the most commonly misdiagnosed of the four because the twist is often produced during assembly rather than delivered that way. Over-tightening a joint at one corner, a panel that is not fully seated, or a base frame bolted down before the carcass was squared will all pull the box out of plane. The unit then arrives at the installation with a built-in twist that the installer attributes to the floor.
The consequence of treating a twist with adjustable feet is specific and worth stating plainly: the feet will bring all four corners into contact, the rock will disappear, and the cabinet will stand with its carcass under a permanent torsional load. Doors and drawers will be misaligned at one end, and the joint that was over-tightened will carry the load the feet did not remove. The correct fix is to loosen the carcass, square it, and re-tighten — before anything is attached to the base.
Corner plates, base frames, and mounting hardware
The Floor Deflection Case
Floor deflection is the cause that buyers are least prepared for, because it passes the empty test. A cabinet on a suspended timber floor or a lightweight mezzanine will sit level when it is empty, and will be level no longer once it is loaded — because the floor itself has moved downward under the load, and it has moved unevenly.
The mechanism is that the floor's stiffness is not uniform. Joists run in one direction; a cabinet spanning across joists loads them where they are strongest and carries well, while one standing parallel to joists may sit over a single joist or between two. Adding load deflects the floor locally, the cabinet follows, and the level achieved at installation is lost.
| Floor construction | Behaviour under a loaded cabinet | What to do |
| Concrete slab on grade | Negligible deflection | Feet are sufficient |
| Concrete suspended slab | Very small deflection | Feet are sufficient |
| Timber joists, short span, well braced | Small, uniform deflection | Feet usually sufficient; re-check after loading |
| Timber joists, long span or notched | Visible, uneven deflection | Spread the load over a base plate or bearer |
| Suspended timber with a flexible finish | Large, uneven deflection | Bearer or base frame, plus a load-spreading plate |
| Mezzanine or lightweight steel deck | Large, uneven deflection | Do not use point feet; distribute over a frame |
The remedy is load spreading, not more adjustment. A point foot concentrates the cabinet's weight onto a contact patch of a few square centimetres. Widening that patch with a base plate or a bearer spreads the load across more joists and reduces local deflection. Increasing the thread length does nothing, because the floor moves after installation regardless of how much adjustment is available.
Where the floor moves, a point foot is the wrong component family. This case belongs to base frames and bearers, and the feet then adjust the frame rather than the furniture. Where that distinction is not made, the installation is re-leveled at handover and is out of level within a month — which is the most common version of the complaint that feet "do not hold".
Load-spreading pads, glides, and protection hardware
Sizing the Adjustment Range: The Tolerance Stack
When feet are the right answer, the range is not a guess and it is not the catalogue's maximum. It is the sum of four contributions, plus a margin.
| Contribution | How to measure it | Typical magnitude |
| Floor slope across the run | Straightedge and level over the full run, measure the drop end to end | 0-15mm |
| Local surface irregularity | Straightedge over 300mm at each support position | 1-5mm — tile lips, grout lines, board edges |
| Furniture base out-of-flat | Measured on a flat reference surface | 1-3mm |
| Production build tolerance | From the drawing, or measured on samples | Per drawing |
| Subtotal | Add the four above | |
| Margin | 25-30% of the subtotal | Covers measurement error and settling |
The range must be sized on the subtotal plus margin — and the working position must sit in the middle of the available travel. A leveller specified so that its maximum extension exactly equals the worst-case requirement is working at the top of its travel, where its load capacity is a fraction of its mid-range figure. The consequence is a foot that is simultaneously at its weakest and carrying its heaviest corner.
Range required, by floor slope and run length
| Floor slope | Over 1m | Over 2m | Over 3m | Over 4m |
| 1 mm/m (1:1000) | 1mm | 2mm | 3mm | 4mm |
| 3 mm/m | 3mm | 6mm | 9mm | 12mm |
| 5 mm/m (1:200) | 5mm | 10mm | 15mm | 20mm |
| 8 mm/m | 8mm | 16mm | 24mm | 32mm |
| 12 mm/m (1:83) | 12mm | 24mm | 36mm | 48mm |
The run length, not the cabinet, sets the number. A 5 mm/m slope is negligible under a 600mm cabinet and requires 20mm of correction under a 4m run of base units — the same floor, the same slope, a range requirement that differs by a factor of four. This is why the customary practice of measuring floor level at a single point, or over a 1m straightedge, systematically undersizes the range on long runs.
Two qualifications on the table
A fall can be intentional. Wet rooms, bathrooms, balconies, and commercial kitchens are frequently built with a deliberate fall of 1:100 to 1:200 for drainage — 5 to 10 mm/m, by design. Detecting it and treating it as a defect leads to a specification argument. Detecting it and sizing the feet for it is the correct response.
Building standards set a tolerance, not a guarantee. Floor level tolerances in most standards are expressed over a defined length rather than as an absolute, and they describe what a new floor must not exceed. Existing buildings routinely exceed them, and refurbishment work encounters floors far outside any standard. Measure the floor you have, not the floor the standard permits.
Threaded inserts and sockets for leveller interfaces
What Adjustable Feet Cannot Fix
Stating the limits is more useful than another selection table.
| Situation | Why feet cannot fix it | The correct response |
| Carcass twist | Leveling the base moves the twist into the door line | Loosen, square, and re-tighten the carcass; check the base frame |
| Floor deflection under load | The floor moves after installation, by an amount no range anticipates | Base frame or bearer plus load-spreading plates |
| A floor with a 40mm step within the footprint | No foot spans a discontinuity; the unit is bridging an edge | Relocate, or build a leveled platform |
| A very soft or resilient finish | The finish compresses unevenly and permanently | A load-spreading base with a large contact area |
| An item that must be moved regularly | Adjustment is lost every time it is relocated | A caster system with a levelling foot, not a leveller alone |
| Load above the mid-range capacity of the chosen foot | Extension reduces capacity faster than range increases it | Go up a size or a family, or reduce the unsupported height |
The pattern: adjustable feet correct the relationship between the base and a floor that is stable but not level or not smooth. They cannot correct a base that is not flat, a floor that moves, or a discontinuity in the floor. Those three cases account for most of the installations where leveling "does not hold", and each has a different remedy.
Installation and Verification
The leveling procedure itself is short, and three details decide whether it holds.
The verification that matters is the door line, not the level. A spirit level across the cabinet base confirms the base is level. It does not confirm the carcass is untwisted. Check that doors close evenly along their full height and that drawer fronts are parallel — a twist that the feet have hidden will show there first, and it is the symptom the customer will report.
Specification Notes
| Specify | Why |
| The measured slope across the full run | The run length sets the range, not the cabinet footprint |
| Local irregularity at each support position | Point deviation, not slope, is what makes a unit rock |
| Whether the floor deflects under load | Determines whether feet are the right family at all |
| The working range, not the maximum travel | Capacity falls sharply toward full extension |
| The base contact area required | Load spreading on soft or flexible floors |
| Anti-vibration or locking requirement | Vibration releases a friction-only lock |
| Material and finish for the environment | Kitchens, bathrooms, and outdoors each demand a different finish |
We manufacture adjustable feet, levellers, and connecting levellers in zinc alloy, steel, and stainless steel 304/316, with documented load ratings stated at mid-range extension rather than maximum travel, adjustment ranges to stated tolerance, and corrosion performance tested to EN 1670. Load testing follows ASTM protocols, and mid-range load figures for each model are available so that specification is based on the working position rather than the catalogue maximum.
Send us your measured floor profile and load per foot
Conclusion
Furniture that will not sit still has four possible causes, and only two of them are floor conditions that adjustable feet correct. Separating them takes ten seconds — count how many supports touch and whether the lifted pair is diagonal — and the answer determines whether you should be buying feet or re-squaring a carcass.
Where feet are the right answer, the range is an arithmetic result, not a catalogue maximum: floor slope over the full run, plus local irregularity at each support, plus the base's own out-of-flatness, plus build tolerance, plus a margin. And the working position must sit in the middle of the travel, not at the top of it.
Key takeaways:
Engineered base and support assemblies
Additional Resources
- Adjustable Feet, Levellers, and Connecting Levellers
- Load-Spreading Pads and Protection Hardware
- Threaded Inserts and Sockets
- Floor Profile and Load Consultation
- ISO 9001 Manufacturing
About Shaxi Hardware
With over 15 years of experience manufacturing furniture hardware, Shaxi Hardware serves brands and manufacturers across 40+ countries. Our ISO 9001 certified production facility manufactures adjustable feet, threaded levellers, connecting levellers, plinth feet, and base support hardware in zinc alloy, steel, and stainless steel 304/316, with documented load ratings stated at working extension, adjustment ranges to stated tolerance, and corrosion performance tested to EN 1670. Load testing follows ASTM protocols, and custom interfaces, base geometries, and finishes are available through our OEM engineering service.
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