Legal dimensions weights and overhangs for a trailer

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This guide is to give the law regarding weights and legal dimensions for a trailer to help you either build a trailer or tow legally


The most important thing to think of when building a trailer is the weight you need to carry as you do not want to have your trailer collapse as you are towing it and also you don't want to be have a fine for being over weight.

The law regarding weight of a trailer for use on the public highway.

You can not have a trailer gross over 750 kg without brakes 

You can not gross over 3500kg with brakes.

The gross train weight also can not be more than the gross train weight marked on the towing vehicle.

All trailers must have the gross weight marked on it.

This means that you have to take in careful consideration what you will be loading on to the trailer and how much it weighs all components must be capable of caring the weight you will be carrying. The gross weight of the is trailer the weight that the weakest part of the trailer can take. This means if you have tyres rated at 1000kg total and the axles are rated at 1300kg and the coupling is rated at 2000kg the trailer should have a gross weight of 1000kg.


There is not a lot you need to know about dimensions as the law does allow very large trailers.

If the towing vehicle has a gross weight of or below 3.5 Tonnes

The maximum length is 7m excluding Coupling and drawbar

Maximum width 2.55m (changed 2010)

If the gross weight of the towing vehicle exceeds 3.5 tonne

The maximum length of trailer is 12m excluding coupling and drawbar

Maximum width 2.55m

Max length of towing vehicle and trailer 18m

Overhang of loads

You can overhang the trailer with your load but you must follow the following guide lines.

Up to 1m rear over hang is ok but we recommend it is clearly marked.

From 1m - 2m rear overhang MUST be clearly marked.

From 2m - 3.05m a marker board must define the end of the load and it must be illuminated at night.

Your load must not project more than 305mm either side of your trailer and not give an overall width of over 2.9m

If you need to exceed any of these overhangs you can but it is classed as an abnormal load and you need to inform the police

Maximum height

There is no maximum height for a trailer but to keep the trailer stable it is recommended not to exceed 3m high or 1.7times the track of the trailer.

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