Caster floor pressure depends on the force carried by one wheel and the area where its tread contacts the floor. Wheel material affects that contact, but a material name alone does not establish the pressure under a particular loaded wheel.
The reference table below provides manufacturer-published values for comparing tread categories. Use the calculation tables for equipment-specific estimates. Neither table provides an allowable pressure for a floor or a load rating for a complete caster assembly.
Floor Pressure Reference Values by Wheel Type
Blickle publishes the following average floor-pressure reference values in its wheel series information. The manufacturer defines average pressure as radial force divided by wheel contact area. These are material-category reference values—not measured results for your equipment, universal material constants, or floor acceptance limits. The source does not specify a wheel model, applied load, or contact-patch dimensions alongside each pressure value.
| Wheel or tread category | Published reference pressure, N/mm² | Approximate equivalent, psi |
|---|---|---|
| Pneumatic tire / soft rubber | 0.8 | 120 |
| Elastic solid rubber | 1.8 | 260 |
| Super-elastic solid rubber | 1.5 | 220 |
| Standard solid rubber | 3.5 | 510 |
| Soft thermoplastic polyurethane (TPU) | 4.0 | 580 |
| Thermoplastic rubber-elastomer (TPE) | 4.5 | 650 |
| Polyurethane, 75 Shore A | 3.5 | 510 |
| Polyurethane, 92 Shore A | 8.0 | 1,200 |
| Hard thermoplastic polyurethane (TPU) | 11.0 | 1,600 |
| Polypropylene / nylon | 40.0 | 5,800 |
| Cast nylon | 60.0 | 8,700 |
| Cast iron / steel | Greater than 350 | Greater than approximately 51,000 |
Source values are reproduced from Blickle; psi equivalents are calculated using (1\ \text{N/mm}^2 \approx 145.038\ \text{psi}) and rounded to two significant figures. The rounding does not add precision to the original reference data.
The table shows why tread construction matters: Blickle assigns substantially different reference pressures to its 75 Shore A and 92 Shore A polyurethane categories. It also lists soft TPU separately from hard TPU. “Polyurethane” is therefore not a sufficiently specific description for a floor-pressure comparison.
Use these values to identify candidates for further investigation. Do not substitute a reference value for the actual contact area of a selected wheel, or reverse-calculate a contact patch and treat it as measured data.
Calculate Average Pressure Under One Loaded Wheel
The calculation concerns the wheel-to-floor interface. The input is the downward force carried by one wheel—not the total cart weight and not the caster’s catalog load capacity.
Average contact pressure is:
[
p_{\text{avg}}=\frac{F_w}{A}
]
where:
- (p_{\text{avg}}) = average contact pressure, in psi;
- (F_w) = downward force carried by one wheel, in pounds-force (lbf);
- (A) = loaded wheel contact area, in square inches (in²).
This force-divided-by-contact-area method matches Blickle’s published definition of average floor pressure. It does not calculate the peak pressure within the patch.
For an approximately rectangular footprint:
[
A \approx b_c \times L_c
]
where (b_c) is the actual contact width across the tread and (L_c) is the contact length along the direction of travel, both in inches.
The Caster Floor Point Load Calculator accepts load per wheel in lbf, tread width in inches, and contact-patch length in inches, and reports pressure in psi and psf. A rectangular footprint estimate is appropriate only when the width and length represent the loaded contact reasonably well. A catalog tread width can overstate contact width for a crowned tread or a wheel that does not bear across its full face.
Use average pressure as a screening result. It does not describe local peaks, impact at a joint, or the pressure distribution while a caster swivels.
Unit Conversions
[
p_{\text{psf}}=144\times p_{\text{psi}}
]
[
p_{\text{N/mm}^2}=\frac{p_{\text{psi}}}{145.038}
]
Here, psi means lbf/in² and psf means lbf/ft². Converting between them changes the unit, not the physical load case: contact pressure expressed in psf is still pressure over the wheel’s small footprint.
If a load record uses “lb,” confirm whether it identifies weight force or mass. Use lbf for this calculation. For mass supplied in kilograms, convert to force using (F=mg), then keep force and area units consistent.
Contact-Patch Calculation Examples
The following are hypothetical stationary, single-wheel cases on a level surface. They are not test results or assigned performance values for particular wheel materials. Each example assumes that the stated width and length form a fully contacting rectangle.
| Case | Wheel load, lbf | Contact width, in | Contact length, in | Contact area, in² | Average pressure, psi | Average pressure, psf |
|---|---|---|---|---|---|---|
| A: shorter footprint | 300 | 2.0 | 0.10 | 0.20 | 1,500 | 216,000 |
| B: longer footprint | 300 | 2.0 | 0.30 | 0.60 | 500 | 72,000 |
| C: higher load, same assumed footprint as B | 450 | 2.0 | 0.30 | 0.60 | 750 | 108,000 |
For Case B:
[
A=2.0\times0.30=0.60\ \text{in}^2
]
[
p_{\text{avg}}=\frac{300}{0.60}=500\ \text{psi}
]
[
p_{\text{psf}}=500\times144=72{,}000\ \text{psf}
]
Cases A and B isolate contact-area sensitivity: at the same force, tripling the assumed area reduces average pressure to one-third. Case C isolates load sensitivity with area held constant.
A real tread’s footprint may change when its load changes. Case C is therefore a mathematical comparison, not a prediction that a wheel’s contact area remains fixed between 300 and 450 lbf. The calculator page likewise notes that actual patch shape changes with load, hardness, and floor conditions.
Establish the Wheel Load and Contact Area
A useful pressure result requires inputs tied to the same equipment configuration and operating condition.
Determine the Force Carried by the Wheel
Include both equipment weight and payload when establishing wheel reactions. Dividing total weight by the number of wheels is an equal-sharing assumption, not a measurement. An offset payload, uneven floor, frame flexibility, or differences in wheel height can change the load carried by individual wheels.
For a stationary assessment, use measured wheel reactions or an equipment-specific load-distribution calculation. If measuring, use appropriately rated wheel-load scales or load cells with the equipment supported at consistent elevations; raising only one wheel onto a scale can change the distribution being measured.
For dual-wheel casters, distinguish the reaction at the caster assembly from the force carried by each wheel. Do not assign the entire assembly reaction to each wheel or assume equal sharing without a basis.
A stationary wheel-load reading does not capture impacts, braking, or changing reactions during travel. Identify the condition being assessed rather than adding an unsupported universal multiplier.
Obtain a Footprint for the Relevant Load
First request contact-area data from the wheel manufacturer for the exact wheel model, tread construction, applied force, and relevant temperature. A material description or hardness number is not contact-area data.
If suitable data are unavailable, a stationary footprint measurement can support an initial estimate:
- Secure the loaded equipment against unintended movement using an appropriate procedure.
- Use a floor-compatible impression medium or pressure-sensitive film within its specified measurement range.
- Record the wheel load, floor surface, temperature, and time under load.
- Measure the actual contacting area. For an irregular footprint, trace and calculate its area rather than using only its bounding width and length.
- Repeat the measurement to identify variation and retain the measurement method with the result.
A footprint impression establishes area only to the accuracy of that method. It does not automatically measure peak pressure. A static footprint also does not reproduce rolling or swiveling contact.
Do not use wheel diameter multiplied by tread width as contact area. Diameter describes the wheel’s overall geometry, not the length touching the floor.
Match the Pressure Result to the Floor’s Actual Rating
There is no single allowable caster pressure that applies to all tile, resin coatings, concrete slabs, resilient flooring, or mezzanine systems. Obtain the applicable criteria for the identified floor product and supporting construction.
Keep surface pressure, concentrated force, rolling load, and distributed structural loading separate:
| Floor or system being reviewed | Information needed | What the average-pressure calculation cannot establish |
|---|---|---|
| Resilient flooring | Product-specific indentation data, stationary-load conditions, rolling-load guidance, adhesive and substrate requirements | Whether a parked wheel will leave acceptable indentation after a particular dwell time |
| Ceramic or porcelain tile | Installed tile-system suitability, substrate and bedding details, joint condition, permitted rolling loads | Whether a wheel will crack a tile or damage an edge or joint |
| Resin-coated concrete | Coating-system guidance, cure condition, temperature, and acceptance criteria for wheel traffic | Whether pressure alone predicts coating damage, delamination, or wear |
| Concrete slab | Slab construction, wheel forces and spacing, joint and edge locations, and engineering assessment where needed | Slab bending, local structural response, or joint load transfer |
| Raised access floor | Exact panel and understructure, concentrated-load and rolling-load ratings, test wheel geometry, and route restrictions | Whether the installed system can carry a cart merely because its calculated contact pressure is low |
| Mezzanine | Structural design criteria, total equipment load, wheel reactions and spacing, decking, and support layout | Compliance with a posted uniformly distributed load rating |
For raised access floors, Tate’s Access Floor Installation Manual requires rolling loads to remain within the product data-sheet rating and directs users to obtain guidance when wheel sizes or loads differ from those in the specifications. It also identifies special concerns at cut panels, thresholds, and expansion joints. Those conditions cannot be resolved by a psi calculation alone.
Only compare calculated pressure directly with a supplier’s pressure criterion when the criterion applies to the relevant contact geometry, duration, temperature, and loading mode. A stationary indentation result is not automatically a rolling-load allowance.
Likewise, do not compare the 72,000 psf contact pressure in Case B with a mezzanine’s posted psf rating. The former acts over 0.60 in²; the latter may describe a uniformly distributed structural load over a much larger area. The matching unit does not make the criteria interchangeable.
Record Pressure and Floor-Protection Evidence Separately
Pressure is only one part of a wheel-floor comparison. Record marking, staining, indentation, and mechanical damage as separate outcomes; a “non-marking” product claim does not establish resistance to every form of floor damage.
Use the following fields when comparing actual wheel candidates:
| Comparison field | What to record |
|---|---|
| Wheel identification | Manufacturer, part number, diameter, tread construction, profile, and specified hardness |
| Load condition | Force per wheel, equipment loading arrangement, and whether the assessment is stationary or moving |
| Contact dimensions | Catalog tread width, actual contact width, contact length, or directly measured area |
| Data basis | Manufacturer-supplied, field-measured, or assumed; include the document or measurement reference |
| Calculated result | Average pressure in psi and psf, with rounding appropriate to the inputs |
| Floor identification | Exact surface product or finish, substrate or support system, and installation condition |
| Applicable criterion | Supplier or engineer criterion, units, loading mode, duration, and other stated conditions |
| Marking and staining evidence | Product-specific claims and any documented observations on the actual floor |
| Floor response | Measured indentation or documented scuffing, scratching, cracking, or coating damage under stated conditions |
| Review status | Assumption-based estimate, measurement-supported screening, or documented supplier or engineering determination |
Keep the source document and its revision with each applicable criterion. If contact area is assumed, label the result as an estimate. If the floor criterion is unavailable or applies to a different loading mode, report the calculated pressure without assigning a pass/fail outcome.
A defensible comparison identifies the exact wheel, the force it carries, the basis for its contact area, and the floor requirement being evaluated. Without those connections, a lower pressure number is only a numerical difference—not evidence of floor compatibility.