Caster load capacity guide.
Capacity is the most quoted and least understood number in casters. This guide gives the working formula, the floor rule that invalidates the naive one, and the test-method question that separates real ratings from brochure ratings.
Load per caster = total loaded weight ÷ 3 (not 4 — uneven floors guarantee a three-caster moment), then choose a caster whose dynamic rating exceeds that figure with margin for shock and starting loads. Always ask which test convention the rating follows (EN 12532 / ANSI ICWM): a static rating and a dynamic rolling rating for the same caster are different numbers, and only the dynamic one describes a caster at work.
The formula, worked
Take a loaded cart at 1,200 kg total. The naive division gives 300 kg per caster. The floor-corrected division gives 1,200 ÷ 3 = 400 kg — because crossing a joint, a threshold or a dock plate, one caster unloads and its share lands on the others. Now add the working margin: starting a loaded cart, stopping it, and the small impacts of real floors argue for selecting a caster rated meaningfully above 400 kg per caster in dynamic terms. Buyers who size to exactly the static number discover the difference in their first year of wheel replacements.
Static vs dynamic: the two ratings
- Static rating — the load the caster supports standing still. Always the bigger number, always the one in the headline.
- Dynamic rating — the load at which the caster survives rolling testing: distance, speed, obstacles, per the test convention. This is the rating that describes your use.
- Test conventions — the EN 12527–12532 series (including EN 12532 dynamic testing) and ANSI ICWM standards define how casters are tested so ratings can be compared. A rating without a named convention cannot be compared with anything — treat it as marketing until the method is produced.
What actually fails when capacity is wrong
Under-rated casters rarely collapse theatrically. They fail economically: tread flat-spots and chunks, bearings brinell and turn gritty, forks flex and take a set, raceways notch until swivels steer like bent shopping carts. Each failure arrives as a maintenance ticket, not a catastrophe — which is why under-sizing hides in budgets for years. The divide-by-three rule plus a dynamic rating is cheap insurance bought once.
Special cases
- Powered movement — tugs and AGVs change the load case (drawbar forces, higher speeds); state powered movement in the RFQ.
- Shock environments — dock plates, rails and thresholds argue for the spring caster conversation, not just a bigger number.
- Heat — capacity derates with temperature; high temperature ratings must be stated at the tested temperature, as our heat line does.
- Leveling casters — read capacity in the levelled state, per unit, as the leveling line specifies.
CASTOVELLA quotations state per-caster capacity with its test convention named, and the sample protocol includes load testing against it. If a competing quotation gives you a capacity with no method, you now know the question to ask.
Related guides
Specification first. Price second.
Every guide on this site ends at the same place: a locked specification and a sample that proves it.