To calculate ball transfer unit load capacity, divide the total load by the minimum number of units supporting it at any moment, then apply a safety factor — typically dividing the rated capacity by two or three. The result is the minimum per-unit rating you need. Because a load is rarely shared equally, always size for the worst case where the fewest units bear the weight. Alwayse units span three tiers — light (0–100kg), medium (101–249kg) and heavy (250kg and above), up to 12,000kg.
Getting load capacity right is the single most important step in specifying a ball transfer table. Under-specify and units develop flat spots and fail early; over-specify and you pay more than you need. This guide gives you the method, the safety factor and a worked example, then links to the tools to finish the job.
The support-point rule
A flat, rigid item resting on a ball transfer surface is supported by at least three units at any instant — but as it moves, the number actually carrying the load changes, and at the edges or corners it can drop to as few as three or four. The safe assumption is therefore the minimum number of units in contact under load, not the total number fitted to the table. This is why spacing and layout matter as much as the count, a topic covered in our table design guide.
The calculation, step by step
- Find the total load. Take the heaviest item the table will carry, including any packaging or fixture.
- Decide the minimum supporting units. For most flat loads, assume three to four units bear the weight at the worst point.
- Total load ÷ minimum supporting units = nominal load per unit.
- Apply a safety factor. Divide the unit’s rated capacity by two for steady handling, or by three for shock, impact or continuous duty, and require a unit whose rated capacity comfortably exceeds the nominal load per unit after that margin.
- Select the tier. Match the required per-unit rating to the light, medium or heavy tier using the search tool.
Worked example
Suppose a table must carry a 600kg crate. Assume only four units bear the load at the worst position: 600 ÷ 4 = 150kg per unit. Applying a safety factor of two for steady handling means each unit should be rated to at least 300kg — placing this firmly in the heavy-load tier (250kg+). If the crate is dropped onto the table rather than placed, use a factor of three and specify spring-loaded heavy-duty units to absorb the impact.
Factors that change the answer
- Impact and shock — items placed with force need a higher safety factor and often spring-loaded units.
- Load distribution — point loads concentrate weight on fewer units than evenly spread loads.
- Flexible or uneven items — these may bear on even fewer units; assume the worst case.
- Duty cycle — continuous, high-frequency use favours heavy-duty units for longer life.
For per-unit ratings across the range, see the load and ball ratings guide, and check your layout against the table design guide. For a definitive recommendation, the Alwayse technical team can size a table from your load and layout — call +44 (0)121 380 4700.
Frequently asked questions
How many ball transfer units support a load at once?
A flat, rigid item is supported by at least three units at any moment, but the number changes as it moves and can drop to three or four at edges and corners. Always size for that worst case, not the total number of units fitted.
What safety factor should I use for ball transfer units?
Divide the rated capacity by two for steady, controlled handling, or by three for shock, impact or continuous duty. The selected unit should comfortably exceed the nominal load per unit after applying that margin.
What happens if a ball transfer unit is overloaded?
Overloading causes flat spots on the load ball, rough rotation and early failure. If units show flat spots, the load calculation should be reviewed and higher-rated units specified.