Desk planning · Manual geometry checks

Desk Fit Checker: Clamp and Room Dimensions

See which dimensions meet your stated conditions, which conflict, and what is still unknown. No model database or structural approval.

Enter only what you know. Every field is optional; blank means unknown, not zero. All fields use the selected unit. Use up to 32 characters per dimension; longer input is reported as an error, not clipped. Use decimals (0.5, not 1/2); do not paste units, commas or exponent notation. Supported positive dimensions: 0.001–100,000 mm (about 0.00003937–3937.00787402 in).

1. Thickness — start here

Desktop thickness at the clamp mm

Measure at the actual contact point; include only an explicitly permitted installation stack. Must be greater than zero.

Clamp minimum thickness mm

Use the minimum for the selected clamp hardware/configuration. Known zero allowed.

Clamp maximum thickness mm

Use the maximum for that same configuration. Must be greater than zero.

2. Top and underside contact areas (optional)

Measure flat rectangles at the same clamp location. Separate width/depth checks do not prove alignment, rotation clearance or suitability of a curved edge.

Top flat area width mm

Left-to-right clear flat width, centered at the intended mount position. Known zero allowed.

Top flat area depth mm

Flat top surface depth inward from the rear edge at that same position. Known zero allowed.

Upper clamp footprint width mm

Full required upper contact footprint, left to right. Must be greater than zero.

Upper clamp footprint depth mm

Full required upper contact footprint inward from the rear edge. Must be greater than zero.

Underside flat area width mm

Clear underside width at the same intended clamp position. Known zero allowed.

Underside flat area depth mm

Clear underside depth inward from the rear edge. Known zero allowed.

Lower clamp footprint width mm

Full lower pad/bracket contact footprint width. Must be greater than zero.

Lower clamp footprint depth mm

Full lower pad/bracket contact footprint depth. Must be greater than zero.

3. Rail and rear installation space

Rear edge to nearest underside obstruction mm

Shortest unobstructed inward distance from the rear edge. Include trays, aprons or rails. Known zero allowed.

Required clear insertion depth mm

Conservative depth the clamp needs during insertion and tightening, from its instructions. Known zero allowed.

Available space behind the desk mm

Measured desk-to-wall/obstacle gap; also used in the optional room-depth sum. Known zero allowed.

Required rear installation space mm

Rear clearance needed during installation, including screw/tool access; confirm separately from arm travel. Known zero allowed.

4. Desk and room envelope (optional)

A rectangular footprint check only. The rear gap above is included in the depth total. Leave your allowances blank until measured; entering 0 explicitly requests no allowance.

Desktop width mm

Desktop left-to-right width, excluding the chosen side allowance. Must be greater than zero.

Available room width mm

Clear width of the intended location. Must be greater than zero.

Total left and right space allowance mm

Left plus right allowance together; your measured choice, not a prescribed access minimum. Known zero allowed.

Desktop depth mm

Front-to-back desktop depth. Must be greater than zero.

Available room depth mm

Clear depth before an obstruction or route you must keep free. Must be greater than zero.

Front space for your chair and movement mm

Your actual chair and movement envelope; no ergonomic or accessibility minimum is supplied. Known zero allowed.

No current report. Enter known dimensions or load the synthetic example, then check.

Check each dimension separately before deciding what still needs a manufacturer’s confirmation. A desktop can fall inside a clamp’s thickness range while a rail blocks installation. A desk can fit the available width while its depth, rear gap and your chosen chair allowance exceed the room space.

This checker uses your manually entered measurements, not a product-compatibility database. It never returns a structural approval or a guarantee that a particular arm and desk work together. Start with the desk setup checklist, identify the exact desk, arm and clamp hardware, and gather their instructions before entering dimensions.

What the nine checks mean

Condition	Calculation	What still needs checking
Thickness	Clamp minimum ≤ desktop thickness ≤ clamp maximum	The correct hardware configuration and permitted material/stack
Upper contact width and depth	Each available top dimension ≥ its required clamp dimension	Both dimensions describe the same flat contact area at the intended position
Lower contact width and depth	Each available underside dimension ≥ its required clamp dimension	Rails, bevels and openings do not interrupt that contact rectangle
Underside insertion	Rear edge-to-obstruction distance ≥ required insertion depth	Actual installation path and screw/tool access
Rear installation	Available rear gap ≥ required rear installation space	Full arm and cable movement, checked separately
Room width	Desk width + total side allowance ≤ available room width	Doors, other furniture and the real placement
Room depth	Desk depth + rear gap + front allowance ≤ available room depth	Your actual chair movement and any access requirements

Contact width is left to right; contact depth runs inward from the rear edge. The checker does not rotate rectangles or determine whether separately measured top and underside areas line up. Use a conservative clear insertion envelope: it does not model a rail’s cross-section, the clamp’s shape or an alternative installation route.

The optional room section uses a simple rectangular envelope. The rear gap is the same field used for the rear-installation check. Side allowance means left plus right together. Front allowance is a value you measure for your setup, not an ergonomic recommendation or an accessibility standard supplied by this tool.

Blank, zero and invalid measurements

Every field is optional. Leaving any required input for a condition blank produces Information missing for that condition, not a zero or a passing result. This lets you check thickness while still collecting the clamp footprint drawing.

Known zero is accepted only for the clamp minimum, available flat-area dimensions, obstruction/rear distances, required insertion/rear clearances, and side/front allowances. Zero is meaningful there: an available underside area of zero conflicts with a positive clamp footprint. Actual desk thickness, clamp maximum, clamp footprint dimensions, desk dimensions and room dimensions must be positive.

Enter a plain decimal, such as 12.7 or 0.5. Fractions, unit suffixes, thousands separators, negative numbers, exponent notation and non-finite values are rejected. Positive values must represent 0.001 to 100,000 mm after conversion. A minimum clamp opening greater than its maximum is an input error, not a fit conclusion. Correct highlighted errors before generating a report or switching units.

Changing units preserves physical values in the active form. The result uses canonical millimeters internally and shows rounded values in the selected unit. The JSON includes the canonical values as well as the calculation explanations. Editing a measurement clears the previous report and disables its download/print controls until you check again.

Reproduce the synthetic example

Use Load synthetic example, then Check dimensions. All numbers are invented planning inputs, not specifications for an Ergotron arm or any named desk. The complete example input JSON and expected geometry report are available for comparison. The form does not import arbitrary JSON files; these downloads document the example.

Example condition	Inputs in mm	Expected result
Thickness	Minimum 10, desktop 25, maximum 50	Met; nearest boundary is 15 mm away
Underside insertion	45 available, 60 required	Conflict; short by 15 mm
Rear installation	100 available, 80 required	Met; 20 mm remaining
Room width	1400 desktop + 100 total sides ≤ 1600 available	Met; 100 mm remaining
Room depth	700 desktop + 100 rear + 550 front ≤ 1150 available	Conflict; short by 200 mm

The four contact-area conditions also meet the entered dimensions, giving 7 met, 2 conflicts, 0 unknown overall. That count does not establish structural or installation compatibility. The 550 mm front allowance is a synthetic input, not a recommended minimum.

A condition exactly on a boundary has no spare dimensional margin. The calculator does not add manufacturing or measurement tolerance for you. Its tiny numerical comparison epsilon only handles floating-point conversion artifacts; it is not a physical clearance allowance.

Why the original installation documents matter

Sources checked September 5, 2026. These documents explain the categories of constraints, not the example’s numbers:

Ergotron’s original LX under-mount C-clamp drawing shows separate clamp/arm dimensions, configurations, motion and load notes. It is a legacy drawing marked with a January 2019 revision, not a specification for every LX or LX Pro generation. Find the exact model’s current resources through the manufacturer model/resource entry.
Ergotron’s desk-attachment comparison separates attachment arrangements. Do not copy the dimensions of one clamp style into another style’s fields.
The manufacturer’s WorkFit A installation guide, a different product, explicitly treats mounting-surface strength and cable routing as installation concerns. It illustrates why arithmetic about thickness alone is insufficient; its numeric specifications are not presets here.

The web extract of the model landing page did not expose a complete specification table in this review; no model measurements were inferred from it. Manufacturer materials are not evidence that we installed or tested your proposed setup.

Keep a useful plan without treating it as certification

Download the JSON or print the current report. Both keep the individual results and the unverified checks visible. Keep your own original dimension sources and confirm ambiguous measurements with the desk and arm manufacturers. No field asks you to assert that a structural, load or VESA check passed; those topics stay explicitly unverified by this calculator.

There is no user-input upload, model lookup or persistent browser storage in the checker. Site analytics are described separately in the privacy policy; fixed completion/download labels do not contain your dimensions. The form is not a backup, and a reload may discard it.

For a no-script option, use the printable blank desk worksheet. Related reading: standing-desk dimensions and configuration and choose a work monitor.

Frequently asked questions

Does a dimension condition being met mean the arm is compatible?

No. The tool compares entered dimensions only. Material strength, desk-maker permission, load limits, monitor weight, VESA, hardware and movement remain unverified. Follow the exact manufacturers’ instructions.

What happens when I leave a measurement blank?

Blank is unknown, not zero. A condition with missing inputs says information is missing; other complete conditions can still be calculated. Enter zero only for fields explicitly allowing a known zero.

Does changing from millimeters to inches change the measurements?

The interface keeps canonical millimeter values when switching units. Display values are converted, not reinterpreted. Invalid inputs must be corrected before a unit switch; any old report is cleared.

Are my dimensions uploaded or saved in browser storage?

The calculation and JSON export run locally without uploading dimensions or saving them in browser storage. Site analytics are separate and use fixed event labels, not the measurements. Reloading can discard the form.