How Do I Work Out the Castor Load Capacity I Need?

Choosing the correct castor load capacity is essential for safety, performance and reliability. If a castor wheel is not rated for the load it carries, it may become difficult to move, wear out prematurely or fail under load.

Selecting the correct castor load capacity is essential for safe movement, long service life and reliable equipment performance.

This guide explains how to calculate the minimum load rating required for your castors and wheels.

Quick Answer

For a standard four-castor trolley:

(Equipment Weight + Maximum Load) ÷ 3 = Minimum Load Capacity Per Castor

Example

• Equipment weight = 50kg
• Maximum load = 400kg
• Total loaded weight = (50kg + 400kg) = 450kg

Required Load Capacity PER castor: 450kg ÷ 3 = 150kg

Each castor should therefore be rated to carry at least 150kg.

As a general rule, choose the next available load rating above your calculated requirement.

Step 1: Work Out the Total Loaded Weight

Add together:

• The weight of the trolley, equipment or platform
• The maximum load it will carry

Equipment Weight + Maximum Load = Total Loaded Weight

Example

50kg trolley + 400kg load = 450kg total loaded weight

Always calculate using the maximum possible load, not the average load.

Step 2: Use the Correct Load Capacity Formula

For most standard four-castor trolleys, use this formula:

Minimum load capacity per castor = total loaded weight ÷ 3

Although a trolley may have four castors, the load is not always shared evenly between all four. On uneven floors, one castor may lift slightly or carry less weight, leaving the other three castors to support most of the load.

Example Calculation

Using the example above:

450 kg ÷ 3 = 150 kg

This means each castor should be rated to carry at least 150 kg.

In practice, you should choose the next suitable castor rating above this figure, especially if the trolley will be used on rough floors, outdoors, over thresholds or in demanding conditions.

Why Divide by 3 Instead of 4?

Many people assume that four castors share the load equally. In reality, this rarely happens during normal use.

Dividing by three provides a basic safety allowance for:

• Uneven floors
• Uneven load distribution
• Frame flex
• One castor temporarily losing full contact with the floor

This method is widely used when selecting castors and wheels for trolleys, carts and industrial equipment.

What About Three-Castor Equipment?

For equipment fitted with three castors, each castor should usually be rated to carry around 40% of the total loaded weight.

For example, if the total loaded weight is 300 kg:

300 kg × 40% = 120 kg

Each castor should therefore be rated to carry at least 120 kg.

What About Six-Castor Equipment?

Six-castor trolleys often use a centrally pivoting configuration to improve manoeuvrability on longer or heavier platforms.

A common setup is:

• Four swivel castors at the corners
• Two fixed or rigid castors in the centre

The centre castors allow the trolley to pivot more easily, making it easier to turn and control.

For this configuration to work correctly, the centre fixed castors should usually be either:

• One size larger than the corner swivel castors, or
• Fitted with approximately 25mm of packing plates

This raises the centre castors slightly in relation to the corner castors. The trolley can then pivot on the centre castors instead of dragging all six wheels equally across the floor.

Because the centre castors carry a larger share of the load, they must be rated accordingly.

As a guide:

• Each centre fixed castor should be rated to carry at least 50% of the total loaded weight
• Each outer swivel castor should be rated to carry at least 33% of the total loaded weight

Example

Total loaded weight: 600kg

Centre castors: 600kg × 50% = 300kg each

Outer castors: 600kg × 33% = 198kg each

Always select castors rated above these figures, especially for uneven floors, going over thresholds / kerbs or demanding conditions.

When Should You Choose a Higher Load Rating?

The calculations above provide a minimum starting point. In more demanding applications, a higher-rated castor may be required.

Consider increasing the load capacity if your castors will be used:

• On rough or uneven floors
• Outdoors
• Over thresholds, ramps, kerbs or potholes
• With shock loading
• At higher operating speeds
• With powered towing equipment
• In hot or cold environments
• With unevenly distributed loads
• In safety-critical applications

Most castor load ratings are based on manual movement over smooth, level floors at walking speed. More demanding conditions generally require a higher load capacity.

Load Capacity Is Only Part of the Decision

Choosing the correct load rating is important, but wheel material also affects performance, floor protection and ease of movement.

Rubber Castor Wheels

• Quiet operation
• Good shock absorption
• Suitable for uneven floors

Polyurethane Castor Wheels

• High load capacity
• Good durability
• Helps protect floor surfaces

Nylon Castor Wheels

• Strong and hard-wearing
• Suitable for heavy loads
• Best on smooth floors

Cast Iron and Steel Wheels

• Suitable for very heavy loads
• Resistant to harsh operating conditions
• Can be noisy and may damage floors

Castor Load Capacity Formula Summary

For most four-castor trolleys:

Equipment Weight + Maximum Load = Total Loaded Weight

Total Loaded Weight ÷ 3 = Minimum Load Capacity Per Castor

Then select a castor with a load rating above the calculated result.

Need Help Choosing the Right Castors?

If you are unsure which castors and wheels are suitable for your application, our team can help.

Whether you need heavy-duty castors, industrial castor wheels or specialist solutions for challenging environments, we can recommend the right option for your equipment.

Browse our online range of castors and wheels or contact us for expert advice.