How the Caster Load Formula Works
The calculator applies the standard load formula used across this site and in our caster buying guide:
Rated capacity = (Empty weight + Max load) × Safety factor ÷ Number of casters
- Add empty weight and maximum load — the full weight the casters ever carry.
- Apply the dynamic safety factor — 1.25 standard, 1.5 towed, 2.0 shock. This accounts for lateral and impact forces a static number misses.
- Divide by the number of casters — the per-caster rating you must meet or exceed.
How the Wheel Selector Decides
The recommendation is not a black box — it applies the published rules below, in order. Environment constraints come first (they are exclusions, not preferences), floor type selects tread hardness second, and the per-caster rating sets diameter and bearing class last. These are the same rules laid out in our materials guide and vertical specification pages.
| Driver | Effect on the specification |
|---|---|
| Freezer / sub-zero | Nylon or polyolefin tread; sealed bearings with sub-zero grease; stainless hardware. Standard polyurethane excluded below 32°F. |
| Walk-in cooler (above freezing) | Polyurethane or nylon; sealed bearings recommended for defrost moisture; stainless stems. |
| Washdown / food service | Stainless rig and hardware; sealed swivel and bearings; NSF-listed models where food contact applies. |
| Outdoor / coastal | Stainless or zinc-rich coated rig; solid rubber or polyurethane tread; step up one wheel-diameter class. |
| ESD-sensitive area | Conductive tread compound; verify measured resistance rating on the datasheet. |
| Healthcare / low noise | Soft polyurethane or TPR, non-marking; sealed swivel for quiet, fluid-resistant service. |
| Tile or LVP floor | Soft non-marking tread; larger diameter to spread point load on vinyl plank. |
| Carpet | Hard tread (nylon), largest practical diameter — soft treads plow on carpet. |
| Rated load per caster | Up to 300 lbs: 3–4 in. wheels. 300–900 lbs: 4–5 in. 900–2,000 lbs: 5–6 in., precision or tapered bearings. Above 2,000 lbs: 6 in.+, dual-wheel or kingpinless rigs. |
Treat the output as a starting specification to confirm with your supplier — real applications have constraints (swivel radius, mounting, brakes, chemical exposure) the calculator does not model.
Common Mistakes in Caster Load Calculations
- Forgetting the equipment\'s own weight — people size for the payload and ignore the cart, which can be a third of the total.
- Ignoring dynamic load — a caster rated exactly at the static number fails early once it crosses a threshold or is towed. The safety factor exists for this.
- Assuming even distribution — four casters rarely share load equally; design uneven or safety-critical loads to one fewer contact point.
Load Ratings by Application
Once you have a per-caster rating, match it to the right specification for your environment:
- Hospital beds & medical carts — see hospital bed casters and medical cart wheels.
- Warehouse & heavy industrial — see warehouse casters and heavy-duty casters.
- Tread material for your rating & floor — see the caster materials guide.
Need help specifying casters for your application? Get matched with a supplier free.