How to Calculate the Required Load Capacity for Your Castors

Working out the correct castor load capacity is one of the most important first steps when choosing castors for your equipment. Getting this right ensures safety, smooth operation, and a longer lifespan for your trolley, dolly, or platform.

Why the Castor’s Load Capacity Matters

Working out Castor Load Capacity is important because each castor has a maximum load rating — the amount of weight it can safely carry. However, this rating usually refers to a single castor, not the full set. To avoid failure or uneven wear, you need to calculate how much weight each castor will actually carry when installed on your equipment.

The Basic Required Load Capacity Formula

The most commonly used formula to calculate the minimum required load capacity per castor is:

• Minimum Load Capacity per Castor = Total Weight  ÷ (Number of Castors − 1)
  • The Total Weight must include the load to be carried plus the weight of the equipment

This formula assumes that at any given time, one castor may not be in full contact with the floor (for example, on uneven surfaces), uneven weight distribution of load, or, shock loading from pot holes, kerbs, floor imperfections and the load being dropped onto the equipment.

Example Calculation

If your trolley weighs 50kg and will carry a maximum load of 400kg, the total weight is:

• 50kg + 400kg = 450kg

Assuming a standard 4-castor setup, the calculation would be:

• 450kg ÷ (4 − 1) = 150kg

So, you’ll need castors rated for at least 150kg each.

Choosing the Right Number of Castors

Most equipment uses four castors, but there are exceptions:

• Six castors – often used on long platform trolleys. The two middle castors act as pivots for sharper turning. These centre castors should be a size larger and capable of supporting at least 50% of the total weight since they carry most of the load during turns.
• Three castors – typically found on small, lightweight dollies or circular platforms. In this case, each castor should support at least 40% of the total load.

Selecting Your Castors

Once you know your minimum required load capacity, you can easily narrow down your options. On our website, simply select your load capacity range to see all suitable castors. From there, you can refine your choice by:

• Wheel diameter: 75 mm, 100 mm, 125 mm, etc.
• Bracket type: Fixed or swivel
• Wheel material: Nylon, polyurethane, rubber, cast iron, polypropylene, or phenolic
• Bearing type: Plain, roller, or ball bearing
• Fixing / Mounting type: Single bolt or 4-hole top plate
• Bracket material: Pressed steel, fabricated steel, or stainless steel

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