How to Calculate Caster Load Capacity

Why Four Casters Usually Count as Three

When selecting casters for carts, equipment, or machinery, many buyers simply divide the total weight by the number of wheels.

For example, if a cart weighs 300 kg and uses four casters, it may seem that each caster only needs to support 75 kg.

However, this calculation is often inaccurate. In real working conditions, the load is rarely distributed evenly across all wheels. Because of uneven floors, movement, and weight shifts, only three casters typically carry the majority of the load even when four are installed.

Understanding this principle helps prevent premature wheel wear, equipment instability, and safety risks.

1. Effective Load-Bearing Casters (M)

In engineering calculations, M represents the number of casters that effectively carry the load.

Although equipment may have four wheels, the effective load-bearing number is usually lower. Floors are rarely perfectly level, and when equipment moves or stops, weight shifts between wheels.

Therefore, engineers commonly assume that only three wheels bear the load.

Typical Load Distribution

2. Caster Load Calculation Formula

Once the effective load-bearing number is determined, the required capacity per caster can be calculated:

T = (E + Z) / M

Where:

• T = required load capacity per caster

• E = equipment weight

• Z = maximum load

• M = effective load-bearing casters

This formula helps ensure casters can handle real working conditions.

3. Example: Commercial Freezer

For example, a supermarket ice cream freezer uses four casters.

Known data:

• Equipment weight (E) = 30 kg

• Maximum load (Z) = 150 kg

• Installed casters = 4

• Effective casters (M) = 3

Calculation:

T = (30 + 150) / 3 = 60 kg

This means each caster should support at least 60 kg.

In practice, engineers usually add 20–30% safety margin, so a 75–80 kg rated caster would be more appropriate.

Conclusion

When selecting industrial casters, always calculate load capacity using effective load-bearing wheels rather than the total number installed.

Key points:

• Four casters usually equal three effective load-bearing wheels

• Use the formula T = (E + Z) / M

• Add 20–30% safety margin for real working conditions

Choosing the right caster capacity improves equipment stability, mobility performance, and service life.