Horsebox Payload Calculator
Overloading a horsebox is not only illegal but puts your horses, passengers, and other road users at risk. Use this calculator to estimate your available payload and check whether your planned load is within safe limits.
Calculate your payload
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What is MAM?
MAM stands for Maximum Authorised Mass (sometimes called GVW - Gross Vehicle Weight). It is the maximum total weight your vehicle is legally allowed to weigh when fully loaded, including the vehicle itself, passengers, fuel, horses, and all equipment.
Your horsebox's MAM is set by the manufacturer and can usually be found on the vehicle's V5C registration document, on a plate near the driver's door, or in the owner's manual.
How do I find my horsebox's MAM?
The easiest place to find your MAM is on the VIN plate, which is usually located on the driver's door frame or under the bonnet. It will be listed as "Maximum Authorised Mass", "Gross Vehicle Weight", or similar. You can also find it on your V5C registration document under the "Revenue Weight" field.
How much does a horse weigh?
Horse weights vary significantly by breed and type. As a rough guide: a pony typically weighs around 300 kg, a cob around 500 kg, a lightweight riding horse around 450 kg, a warmblood around 550 kg, and a heavyweight horse around 650 kg. If you are unsure, it is always safest to overestimate.
What happens if I overload my horsebox?
Overloading a horsebox is a criminal offence. If stopped, you could face an on-the-spot fine, penalty points, or even prosecution. Your insurance may also be invalidated, leaving you personally liable for any damage or injury. Beyond the legal consequences, an overloaded vehicle is harder to control, takes longer to stop, and puts increased stress on brakes, tyres, and suspension.
Should I include a safety buffer?
Yes. This calculator includes a recommended 150 kg safety buffer in the results. Manufacturer weights for horses are averages, and it is easy to underestimate the weight of tack, water, fuel, and personal belongings. A safety buffer helps account for these uncertainties and keeps you comfortably within legal limits.