Almost every guide to caravan weights is published by someone who sells caravans. That matters more here than in most topics, because the arithmetic in this article is the arithmetic that makes a brochure look worse. Manufacturers have a commercial reason to keep advertised tare mass low, since a low tare produces an attractive ball weight figure and a headline payload that sounds generous. The number that actually constrains your trip is what remains after you load water, gas, food, clothes, tools and every accessory fitted since the van left the factory.
Most people discover they are over the limit at a weighbridge, years into ownership.
Key Takeaways
- Payload is ATM minus tare, and on many mid-size vans it is a few hundred kilograms rather than the half-tonne owners assume.
- Tare is measured with empty tanks and excludes every accessory fitted after the compliance plate was issued.
- Water weighs one kilogram per litre, so a 90-litre tank is 90kg of your payload budget.
- Exceeding ATM is an offence and can compromise an insurance claim.
- Being within the van’s limits is not enough. Gross combination mass often binds first, even when the van and the tow vehicle each look fine on their own.
The Five Numbers That Matter
The terminology is genuinely confusing, but only five figures do real work.
Tare
The weight of the caravan as it left the factory. Empty water tanks, no gas, no gear, no accessories. This is a factory specification, not a measurement of your van today.
ATM (Aggregate Trailer Mass)
The maximum legal weight of the fully loaded caravan, including the load carried through the towball. This is the ceiling you must not exceed.
GTM (Gross Trailer Mass)
The weight carried by the caravan’s own wheels when it is hitched up. It excludes the ball weight, which has transferred onto the tow vehicle. GTM is always lower than ATM, and the gap between them is the ball weight.
Ball weight (Tow Ball Mass)
The downward force the van applies to the towball. Most caravans tow best at roughly 8 to 12 per cent of total trailer weight, though the manufacturer’s figure governs.
Too little ball weight invites sway at highway speed. Too much overloads the tow vehicle’s rear axle and lightens the front, which degrades steering and braking grip. Critically, ball weight counts against your tow vehicle’s payload, not the van’s.
GCM (Gross Combination Mass)
The maximum combined weight of the tow vehicle and the loaded caravan together, set by the vehicle manufacturer. This is the ceiling for the whole outfit, and it is frequently the limit that binds first.
The Arithmetic Nobody Runs Before Buying
Payload is simply ATM minus tare. The problem is what that number looks like on real vans.
Take a van with an ATM of 2,400kg and a tare of 2,050kg. Payload is 350kg. Now load it:
- Water, 90-litre tank, full: 90kg
- Two 9kg gas bottles, filled: about 40kg including cylinder weight
- Bedding, clothes and towels for two: 40kg
- Food and pantry for a fortnight: 35kg
- Tools, recovery gear, levelling ramps, hoses and leads: 45kg
- Awning mat, chairs and table: 25kg
That is 275kg before a generator, a second battery, a bike rack, a portable fridge or any of the accessories that came with the van at handover but were fitted after the tare was recorded. The remaining 75kg disappears quickly.
This is why the advice to leave a 10 to 20 per cent buffer below every rating is not conservatism. It is the margin that keeps you legal once you have loaded the things you actually travel with.
The tow vehicle has the same problem
A dual-cab ute with a gross vehicle mass of 3,200kg and a kerb weight of 2,300kg has 900kg of payload. Two adults account for around 160kg. A steel bull bar with a winch is another 120kg or so. That is 280kg before the dual battery system, the water, the recovery gear, the fridge, the tools and the passengers in the back seat.
Then add ball weight. A 2,400kg van at 10 per cent puts 240kg on the towball, and every kilogram of it comes out of the tow vehicle’s payload. You are now at roughly 520kg of a 900kg allowance, and you have not loaded the tray.
Why Being Within ATM Is Not Enough
Three separate ceilings apply at once, and you must be under all of them:
- The van’s ATM. Your loaded caravan weight.
- The tow vehicle’s GVM. Its loaded weight, including ball weight and passengers.
- The combination’s GCM. Both together.
GCM is the one that surprises people, because a van and a vehicle can each sit comfortably under their own limits while the pair exceeds the combined figure. GCM is often lower than GVM plus ATM added together, which means the manufacturer never intended you to max out both simultaneously.
The towbar rating and towball rating add two more constraints. Your real limit is whichever of all these numbers is lowest, not the towing capacity quoted in the vehicle brochure.
Things That Quietly Eat Your Payload
- Accessories fitted after the compliance plate. Solar panels, a second spare, a bike rack, a generator box, an upgraded battery system. None of these are in the tare figure, and they permanently reduce what you can carry.
- Water you forgot about. Grey water tanks, a full hot water service and a portable washing machine all hold water that counts.
- The previous owner’s additions. On a used van, the tare on the plate may bear little resemblance to reality.
- Loading position. Weight concentrated behind the axle reduces ball weight and invites sway, even at a legal total. Heavy items belong low and near the axle.
How to Actually Weigh Your Rig
Estimating does not work. The only reliable method is a weighbridge, loaded exactly as you travel, with full tanks and everyone aboard.
Public weighbridges are available at many council waste facilities, transport depots and certified inspection stations. Some caravan clubs and shows run weigh days specifically for this.
To get useful numbers rather than one total, weigh in stages:
- Whole combination, hitched, everyone aboard. This is your GCM figure.
- Tow vehicle alone, unhitched but still loaded. This is your GVM figure.
- Caravan alone, unhitched and standing on its jockey wheel. This is your ATM figure.
- Caravan hitched, with only the van’s wheels on the platform. This gives GTM, and ATM minus GTM gives your ball weight.
Do this once, properly, and record it. Then reweigh after any significant accessory addition.
What This Means When Buying
Payload should influence the purchase decision more than layout does, and it rarely gets the chance.
Ask for the compliance plate figures before committing, on new and used vans alike, and calculate ATM minus tare yourself rather than accepting a quoted payload. On a used van, ask what has been added since it was built. A van at the smaller end of the market with an attractive tare may leave 300kg of usable payload, which is workable for weekends and genuinely tight for extended off-grid travel.
If you are planning a long trip, work backwards from what you intend to carry rather than forwards from what the van is rated to hold. For the gear that realistically goes in, see our guide to essential gear for a caravan road trip around Australia.
Once you are loaded and legal, the road rules are the other half of the picture. See towing laws in Australia and what changes when you cross a border.
Frequently Asked Questions
Does tare weight include a full water tank?
No. Tare is measured with empty tanks. Water is one kilogram per litre, so it comes entirely out of your payload. A van with 150 litres of total tank capacity carries 150kg when full.
What happens if I exceed ATM?
It is an offence, and it can compromise an insurance claim if you have an incident. Beyond the legal position, an overloaded van has longer stopping distances and is more prone to sway, which is the practical risk.
Is the payload figure in the brochure reliable?
Treat it as a starting point. Advertised payload is calculated from factory tare, which excludes accessories fitted at handover or since. Calculate ATM minus tare from the compliance plate, then subtract what has been added.
Can I get a GVM upgrade to fix this?
A GVM upgrade can raise the tow vehicle’s permitted loaded weight, but it does not automatically raise GCM. If GCM is your binding constraint, a GVM upgrade alone may not solve the problem. Check both figures before spending the money.
Does a weight distribution hitch increase what I can tow?
No. It redistributes load from the rear axle toward the front, which improves handling and headlight alignment. It changes no legal rating, and on an overloaded combination it masks the symptom.
Where do I find these numbers?
The van’s figures are on its compliance plate, usually near the entry door or on the A-frame, and in the owner’s manual. The vehicle’s GVM, GCM, towing capacity and towball rating are in the owner’s manual or on the manufacturer’s website.
This guide is general information current as of 2026 and is not legal or engineering advice. Weight ratings are set by the vehicle and caravan manufacturers and are specific to your individual vehicle and van. Always work from your own compliance plate and owner’s manual figures, and confirm your actual loaded weights at a weighbridge rather than relying on estimates or examples.
