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Selecting the right caster starts with understanding how much weight it needs to support. Choosing a caster with insufficient load capacity can lead to premature wear, equipment instability, higher maintenance costs, and even workplace safety concerns.

While load capacity is one of the most important factors in caster selection, it's also one of the most misunderstood. Simply dividing the total weight evenly among all casters doesn't tell the full story. Uneven floors, thresholds, and shifting loads mean that a cart rarely rests evenly on all of its wheels, which is why the industry rule of thumb accounts for one caster potentially bearing no load at all.

In this guide, we'll explain how to calculate caster load capacity and highlight additional factors to consider before making a purchasing decision.

Quick Answer

To estimate the required load capacity for each caster, use this formula:

(Equipment Weight + Maximum Load) ÷ (Number of Casters − 1) = Minimum Load Capacity per Caster

This rule of thumb exists because uneven floors, load distribution, and towing conditions can cause one caster to momentarily lift or bear little weight — meaning the remaining casters must be capable of supporting the full load between them. For example, a 4-wheeled cart is calculated as though only 3 casters are bearing the load.

Note: This formula applies to standard four-caster applications, such as carts with a caster at each corner. Other configurations, like tilt carts with six casters (four on the corners and two in the center), distribute weight differently and require a different calculation. For non-standard configurations, contact the Colson Group team for help determining load requirements.

Step 1: Determine the Total Weight

Start by calculating the maximum weight the caster must support.

Include:

• Empty equipment weight
• Maximum payload
• Permanently mounted accessories
• Any additional equipment carried during normal operation

Using the maximum expected weight, not the average, helps ensure the caster performs reliably under real operating conditions.

Step 2: Divide by One Fewer Than the Total Number of Casters

Rather than dividing evenly across every caster, the industry rule of thumb assumes one caster may not be bearing weight at any given moment — due to uneven floors, thresholds, or shifting loads during towing. To account for this, divide the total weight by the number of casters minus one:

Total Weight ÷ (Number of Casters − 1)

Using the example above, on a 4-wheeled cart:

1,050 lbs ÷ 3 casters = 350 lbs per caster

This means each caster should be rated to support at least 350 lbs, even though the cart has four casters total.

Step 3: Account for Real-World Conditions

The N-1 calculation already accounts for a meaningful margin for uneven weight distribution, but other operating conditions can impose additional stress on individual casters. Consider:

• Rough or uneven flooring
• Shock loading
• Frequent turning
• High travel speeds
• Continuous operation
• Thresholds and ramps

These conditions can further increase the stress on individual casters beyond the baseline N-1 calculation.

Step 4: Consider Additional Safety Margin

For demanding applications — heavy shock loading, outdoor terrain, or continuous multi-shift operation — many buyers select a caster rated above the N-1 minimum to provide extra reliability and service life.

Using the earlier example:

Rather than selecting the smallest acceptable caster, choosing a higher-capacity option often improves long-term reliability.

Common Mistakes When Calculating Load Capacity

Avoid these common errors when sizing industrial casters:

Dividing by the Full Number of Casters

Assuming all casters share the load equally overlooks uneven floors and shifting weight — use the number of casters minus one instead.

Using the Empty Equipment Weight

Always calculate based on the maximum operating weight, not the unloaded weight.

Ignoring Dynamic Loads

Movement creates additional forces that static calculations don't capture.

Forgetting the Operating Environment

Rough floors, ramps, thresholds, and outdoor surfaces can increase the load experienced by individual casters.

Choosing the Smallest Rated Caster

Selecting a caster with little to no margin above the N-1 minimum may lead to premature wear and more frequent replacements.

Load Capacity Checklist

Before selecting a caster, confirm:

• ✔ Maximum equipment weight
• ✔ Maximum payload
• ✔ Total number of casters (calculate using N-1)
• ✔ Floor conditions
• ✔ Frequency of movement
• ✔ Indoor or outdoor use
• ✔ Shock loading
• ✔ Appropriate margin above the minimum

Best Choice by Application

While the load calculation process is similar across industries, different environments may require additional considerations.

Note: Load capacity is only one part of caster selection. Wheel material, bearing type, wheel diameter, floor conditions, and the operating environment all contribute to overall performance.