Three weights, one plate
The definitions below are paraphrased from Vehicle Standards Bulletin 1, the federal Department of Infrastructure’s guide to trailers with an ATM of 4.5 tonnes or less. It is written to help manufacturers, and it sets out what each term means.
Tare mass (under review). The trailer empty and ready for service, with its standard equipment and any options fitted. Fluid reservoirs are counted as full, but a caravan’s water and waste water tanks are not treated as fluid reservoirs. It includes the weight resting on the tow vehicle.
Gross trailer mass (GTM). The most the fully loaded trailer may put through its own tyres, set by the manufacturer. It leaves out the weight on the tow vehicle.
Aggregate trailer mass (ATM). The total mass of the trailer carrying the maximum load its maker recommends, through the tyres and the coupling together.
Tow-ball down-weight. With the trailer at maximum load and loaded as its maker specifies, ATM minus GTM equals the tow-ball down-weight.
The bulletin makes two further points. ATM and GTM are ratings the manufacturer works out, so they cannot be measured on a weighbridge. And ATM minus tare is the most the trailer can carry: the bulletin’s own illustration is a car trailer with a 700kg tare and a 2,000kg ATM, which can carry a car of up to 1,300kg.
The words are not always used the same way. VicRoads’ trailer page describes ATM as “commonly called gross trailer mass”, while the federal bulletin treats the two as separate ratings. When a form or a seller says “gross”, check which figure on the plate they mean.
Brakes follow the GTM
The bulletin sets braking requirements by GTM, not ATM, and notes that its braking section is under review. In summary:
- 750kg GTM or less
Brakes are not required.
- Over 750kg GTM
An efficient service braking system. Apart from over-run brakes, it must be worked by a control signal from the tow vehicle.
- Up to 2,000kg GTM
Over-run brakes may be used, and braking on one axle is allowed.
- Over 2,000kg GTM
The brakes must work on all wheels, and the trailer needs breakaway brakes that apply at once if it comes off the tow vehicle and stay on for at least 15 minutes.
What each state asks of a caravan
The steps for registering any trailer are on the trailer plate. These are the points each state’s pages make about caravans and camper trailers in particular.
New South Wales
Service NSW says a caravan or camper trailer weighing from 255kg up to 4.5 tonnes automatically gets a 40% reduction on the vehicle tax when it is registered, and that caravans and camper trailers are exempt from stamp duty.
The inspection report has to be a Heavy Vehicle Authorised Inspection Scheme report if the ATM is more than 2 tonnes, and no more than 42 days old.
Victoria
VicRoads says how you register depends on the ATM. You can find it on the manufacturer’s trailer identification plate or the Register of Approved Vehicles, from the manufacturer, or from a Vehicle Assessment Signatory Scheme signatory. Over 4.5 tonnes, the caravan is a heavy vehicle with its own registration steps.
Queensland
A safety certificate is needed for trailers, including caravans, with an ATM between 750kg and 4,500kg, when the registration is transferred to a new owner, moved to Queensland from another state or territory, or when an unregistered one is re-registered. Transport and Main Roads lists the inspection fee for trailers over 750kg up to 4,500kg ATM as $51.45, as at 1 July 2026.
A caravan fitted with gas needs a gas inspection certificate less than 3 months old from an authorised installer when it is registered, unless it is new and its gas fittings were installed by the maker, and Queensland says caravans and motorhomes are not exempt from providing one when the registration is transferred. There is no vehicle registration duty on transferring a caravan or trailer.
Pages: Register your trailer or caravan, Safety certificates
Other states and territories
The rules elsewhere vary; the agencies’ pages are listed on the home page.