Caravan weights come down to six numbers: Tare, ATM, GTM, GVM, GCM and tow ball weight. Your rig is legal when the loaded caravan stays under its ATM, the loaded tow vehicle stays under its GVM, and the two together stay under the GCM. If those three sentences already feel like alphabet soup, you are in good company. We have been on the road since 1992, and weights are still the question we get asked most at shows and campsites.
This guide explains each number in plain English, shows you where to find them on your own rig, and covers the traps that catch experienced travellers, not just newcomers. When you are done, our free Rig Ready weight check will walk you through your own numbers and give you a personal report.
The six weights that matter
Tare mass
What your caravan weighed when it left the factory: empty tanks, no gas in the bottles, none of your gear. It is the starting point for everything else. Be aware that dealer-fitted extras added after manufacture (annexes, extra batteries, solar) are usually not included in the Tare on the plate.
ATM (Aggregate Trailer Mass)
The maximum your caravan is allowed to weigh fully loaded and sitting on its own, not hitched to the car. This is the big one for the van. Everything counts towards it: water, gas, food, tools, bikes, the lot.
GTM (Gross Trailer Mass)
The maximum weight the caravan’s axles can carry while it is hitched up. When the van is coupled, some of its weight transfers to the car through the tow ball, so GTM is always lower than ATM. As a rule of thumb, ATM equals GTM plus the tow ball weight.
Tow ball weight
The downward force the coupling puts on your car’s tow ball. For most Australian vans it sits around 10 per cent of the loaded van weight, though every van is different. Too little makes the van unstable and prone to sway. Too much overloads the rear of the car. And here is the trap: tow ball weight counts towards your car’s GVM, not just its towing capacity.
GVM (Gross Vehicle Mass)
The maximum your tow vehicle is allowed to weigh fully loaded: passengers, luggage, accessories, the bull bar, the drawers in the back, and the tow ball weight pressing down from the van. This is where many otherwise careful setups come unstuck. A big van with a heavy ball weight can push a loaded ute or wagon over its GVM even though the van itself is legal.
GCM (Gross Combination Mass)
The maximum the whole rig, car plus van, is allowed to weigh together, set by the vehicle manufacturer. Some vehicles cannot tow their maximum rated trailer weight and carry a full load at the same time, because the GCM runs out first. Checking GVM and towing capacity separately is not enough; the GCM ties them together.
Where to find your numbers
Your caravan’s Tare, ATM and GTM are on the compliance plate, usually on the drawbar or inside a front boot or door frame. Your car’s GVM, GCM, towing capacity and maximum tow ball weight are in the owner’s manual and on the vehicle’s build plate. If the van has had a factory or engineering upgrade, go by the newest plate.
Payload: the number that is not on any plate
Payload is simply ATM minus Tare: how much you are actually allowed to load into the van. On many vans it is smaller than people expect, and water is the silent killer. A full 95 litre tank is roughly 95 kilograms before you have packed a single tub. If you carry full water plus tools, chairs, an annexe and a generator, it is surprisingly easy to use up the whole allowance.
How to check your real weights
The plates tell you your limits. Only a scale tells you your reality. A public weighbridge will give you the essentials for a few dollars: drive on hitched, unhitched, and car only, and you can work out van weight, ball weight and car weight. Mobile caravan weighing services go further and weigh each wheel individually, which also shows up left-to-right imbalances. Either way, weigh the rig loaded as you actually travel, not empty.
Not sure what to do with the numbers once you have them? Our free Rig Ready check covers caravans, camper trailers, fifth wheelers, motorhomes and slide-ons. Answer a few plain-English questions and it builds you a personal report, plus a printable weight card to keep in the glovebox.
What happens if you are overweight
An overweight rig stops longer, sways easier and works everything harder, from tyres to bearings to the car’s driveline. Beyond safety, penalties apply in every state and territory, and an overweight rig can create serious complications with your insurer after an accident. We wrote more about this in Is My Rig Overweight?, including the warning signs to watch for.
The good news: most weight problems are fixable without buying a new van. Travelling with less water on travel days, moving heavy gear from the van to the car (or the reverse, depending on which limit you are near), and being honest about what never gets used are the usual first steps.
Get your rig sorted before the next trip
Weights are one of those jobs that feels hard until you do it once. Run your numbers through the free Rig Ready weight check, book a weighbridge visit, and you will tow with a lot more confidence. Then the fun part: finding somewhere to take it. The Camps Australia Wide App puts 16,000+ personally checked campsites and caravan parks in your pocket for the trip itself.
Caravan weights FAQs
What is the difference between ATM and GVM?
ATM is the maximum loaded weight of your caravan on its own, and GVM is the maximum loaded weight of your tow vehicle. They are separate limits for separate parts of the rig, and you need to be under both. The tow ball weight of the van counts towards the car’s GVM, which is how a legal van can still make the car overweight.
Does tow ball weight count towards my car’s GVM?
Yes. When the van is hitched, its ball weight presses down on the back of the car and counts as load on the vehicle, so it comes out of your car’s GVM allowance. This is one of the most common reasons a rig is overweight even when the van itself is under its ATM.
Where do I find my caravan’s ATM and Tare?
On the compliance plate, usually mounted on the drawbar or inside a front boot or door frame. If the van has been upgraded, go by the newest plate. Your tow vehicle’s GVM, GCM and towing capacity are in the owner’s manual and on the vehicle’s build plate.
What is a safe tow ball weight for a caravan?
Most Australian caravans are designed to run a ball weight of around 10 per cent of the loaded van weight, but the right figure depends on your van and your car’s maximum ball rating. Too little causes sway, too much overloads the rear of the car. The only way to know your actual ball weight is to measure it with a ball weight scale or at a weighbridge.
How do I weigh my caravan and car?
Use a public weighbridge or a mobile caravan weighing service, with the rig loaded the way you actually travel. At a weighbridge, weigh the car and van hitched, the van on its own, and the car on its own, and you can work out every number you need. Mobile services weigh each wheel and pick up imbalances a weighbridge cannot see.
Is it illegal to tow an overweight caravan in Australia?
Yes. Exceeding your ATM, GVM, GCM or ball weight limits is an offence in every state and territory, and penalties vary by state. Just as importantly, an overweight rig is harder to stop and control, and being over your limits can create serious problems with your insurer if you are in an accident.
Can I increase my car’s GVM or my van’s ATM?
In many cases yes, through certified GVM or ATM upgrades done by approved engineering firms, and some manufacturers offer factory upgrades. Rules differ depending on whether the upgrade happens before or after first registration, and they vary by state, so talk to a certified upgrade provider before spending money. An upgrade is not a free pass either: axles, tyres and brakes all have their own ratings.
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