Caravan Weight Audit: 7 Limits, 5 Readings, One Weighbridge Trip

A legal car and caravan has to sit inside seven main weight limits at once: the caravan’s ATM and GTM, the tow ball limit, the tow vehicle’s GVM and rear axle rating, its GCM and its towing capacity. Most of those numbers are printed on plates and in the owner’s manual. The rest come from one trip to a public weighbridge, loaded the way you travel.

Roadside checks suggest plenty of rigs fail at least one. In January 2017, a two-day roadside check near Orbost, run by Victoria Police with VicRoads, weighed 71 caravans and found 41 over one or more ratings (ATM, GTM or ball weight), RV Daily reported. In July 2022, Queensland Country Life reported that a police operation at Longreach found nine out of 10 caravans overweight.

Those were small, targeted checks, not national surveys, and we could not find a government data set that measures the problem across Australia. What they show is a pattern: owners who believe they are legal, and are not. The audit below needs your paperwork and one weighbridge visit, and a weigh at the public weighbridges we checked costs from $24. Here is how to do it, step by step.

What you need before you start

• Photos of three plates: the caravan’s vehicle plate (often on the drawbar), the tow vehicle’s compliance or vehicle plate, and the towbar’s rating plate.
• The tow vehicle’s owner’s manual, open at the towing section.
• The caravan’s handbook, if you have it, for its tyre and coupling details.
• A notebook or phone with the seven limits and five readings ruled up (the calculator at the end of this guide has the same layout).
• The rig loaded for a real trip, with the people who travel in it.
• A booked or confirmed public weighbridge, and somewhere flat nearby to unhitch.
• Optional: a tow ball weight scale, if your weighbridge cannot weigh the car and van separately.

Step 1: Read the caravan’s plate

Start at the drawbar. According to the federal guide for trailers with an ATM of 4.5 tonnes or less, Vehicle Standards Bulletin 1, “both the vehicle plate and the RAV list ATM, GTM and tare mass” (the RAV is the federal Register of Approved Vehicles). Write all three down.

Tare is the van empty but ready for service, with its standard equipment and any options fitted when its tare was set (for vans built under the current rules, when it was entered on the register). Water tanks count as empty. ATM, the aggregate trailer mass, is the most the van may weigh fully loaded, including the weight it puts on the tow ball. GTM, the gross trailer mass, is the most the loaded van may put through its own tyres while it is hitched, so it leaves the tow ball weight out.

Two things follow. First, ATM minus tare is your payload: everything you can add, from water and gas to the cutlery. Second, VSB 1 points out that ATM and GTM “cannot be measured on a weigh-bridge”. They are ratings. What you measure is the van’s actual mass, and you compare it with them.

While you are there, check the van’s tyres. Transport for NSW lists the maximum rated carrying capacity of the tyres among the limits a loaded trailer must stay under.

If it fails: with no plate, or an unreadable one, there is nothing to audit against. Ask the manufacturer or dealer for the figures before you go any further.

Step 2: Read the tow vehicle’s plate and manual

Now the tow vehicle. These numbers all come from the vehicle manufacturer, and you will find them in the owner’s manual, usually in the towing section. Western Australia’s Safe Towing Guide notes the GVM can be found either there “or on the vehicle compliance plate”.

• GVM, the gross vehicle mass: the most the vehicle may weigh fully laden, as defined in the Australian Design Rules. Some passenger vehicles call it the maximum loaded vehicle mass.
• GCM, the gross combination mass: the most the loaded vehicle and loaded caravan may weigh together. Not every vehicle comes with one. Transport for NSW says that where a GCM is specified, you must not exceed it.
• Towing capacity: the heaviest trailer the manufacturer approves, with braked and unbraked figures.
• Maximum tow ball load: the manufacturer’s limit on the weight pressing down on the ball.
• Axle ratings: the most the front and rear axles may each carry. The rear is the one towing tests.

The GCM deserves a closer look. The WA guide’s own example uses a vehicle with a 2,740kg GVM, a 4,600kg GCM and a 2,250kg trailer limit. Load both to the maximum and the pair weighs 4,990kg, which is 390kg over the GCM even though each half is legal on its own.

If it fails: you cannot judge the rig without these figures. If the manual is missing, the manufacturer or a dealer can supply them for your exact model and variant. Our guide to vehicles that can legally tow 3.5 tonnes shows how much they vary.

Step 3: Read the towbar plate and set your tow ball limit

The towbar has its own ratings. Transport for NSW says a towbar should be clearly and permanently marked with its maximum rated capacity, the vehicle it is made for or a part number, and its maker.

Your working tow ball limit is the lower of the vehicle manufacturer’s figure and the towbar’s. The WA guide puts it plainly: the download on the tow bar “must not exceed the maximum load for the vehicle/tow bar design”.

Check the coupling and ball too. VSB 1, citing AS 4177.3, lists three ratings for 50mm ball couplings: 750kg, 2,000kg and 3,500kg of ATM, and each coupling must be marked with its rating. The WA guide adds that common 50mm tow balls are not rated beyond 3,500kg, so a heavier van needs a coupling rated to its ATM. If you use a weight distribution hitch, NSW advises checking with the towbar maker first; our weight distribution hitch guide explains why.

If it fails: a ball load over the lower rating exceeds the vehicle or towbar rating, and if the coupling is rated below the van’s ATM the setup is not compliant however light you pack.

Step 4: Find the lowest towing limit

Before anything goes on a scale, work out what your combination may actually tow. NSW’s towing ratio rule says the loaded mass of the trailer must not exceed the lesser of the towbar and coupling rating, the vehicle’s towing capacity, the trailer’s own carrying capacity and the tyres’ rating. Transport for NSW adds the GCM, if the vehicle has one.

Its worked example: a vehicle rated to tow 3,000kg, a towbar rated to 3,500kg and a caravan with a 2,500kg ATM. The lowest figure, 2,500kg, is the most that combination may tow. The extra capacity in the car and towbar does nothing for you.

Write down your lowest figure. It may be the van’s ATM, or it may be the car, in which case the van can never legally be loaded to its own ATM behind this vehicle.

Note the expected tow ball load too. The WA guide suggests a download of about 8 to 10 per cent of ATM, up to the tow bar limit; NSW suggests about 5 to 10 per cent of the trailer’s total mass. Both are rules of thumb, and the WA guide notes some European-style vans need less. Your caravan maker’s figure comes first.

If it fails: if the lowest towing limit is below the van’s ATM, your real payload is smaller than the plate suggests, and you need to know that before you pack.

Step 5: Load the rig the way you travel

A weigh-in is only as good as the load on the day. Fill the water tanks you travel with, fit full gas bottles, fuel up, put the bikes and the generator on, and load the tow vehicle’s tray, roof and back seat as you would for a trip. The people who travel in the car get weighed too.

The Longreach police operation found that many owners who thought they were doing the right thing, by weighing the van by itself on a showroom floor or using a cheap weighing instrument, were being misled, according to Constable Chris Curtis, who was manning the weighing station. A van weighed empty at the dealer tells you its tare and nothing else.

How quickly does a payload go? Transport for NSW publishes a packing example for a van with a 2,100kg tare and a 2,500kg ATM, which leaves 400kg of payload. We regrouped its list to show where the kilograms go.

Water, gas and the fitted extras use two thirds of the payload before a single suitcase goes in. The example finishes 58kg over its ATM, and nothing on the list is extravagant.

Whether the fitted extras count against your payload depends on when they went on. VSB 1 counts options fitted when the van was entered on the register as part of its tare. NSW counts after-market add-ons, from TVs to extra gas bottles and awnings, as load. Anything added after delivery, like a drawbar toolbox, comes out of your payload.

There is a second gap. VSB 1 says a builder’s load capacity should include a personal effects allowance of 50kg for each of the first two sleeping berths and 10kg for each extra berth. For a two-berth van that is 100kg for cooking utensils, bedding and luggage. The holiday pack in the NSW example weighs 191kg, almost twice that allowance.

Tip: run this checklist before you drive to the weighbridge. Water tanks filled as you travel. Gas bottles full. Fuel tank as you travel. Grey and black water as you usually carry them. Passengers aboard. Tray, roof racks, drawbar box and bike rack loaded. Jockey wheel working. Weight distribution hitch fitted, with a note of its settings. Photos of all three plates on your phone.

If it fails: weighing a half-packed rig produces a pass you cannot use. The first full trip is the one that counts.

Step 6: Find a public weighbridge and ask two questions

The National Measurement Institute keeps a map of public weighbridges, which it says “are open for public use for a charge under the National Measurement Act 1960”. It also says you must contact the operator for hours and prices. Some, like the two below, sit at council waste and recycling centres.

Prices are modest. Banyule City Council’s public weighbridge in Bellfield, in Melbourne’s north-east, charges $24 up to 5 tonnes and $27 from 5 to 10 tonnes. Mindarie Regional Council’s Tamala Park facility in Perth’s north charges $38 for each certified vehicle or trailer weigh in its 2026/27 fees. Both prices were checked on 27 October 2026.

Before you drive over, ask two questions.

1. Can you weigh the car and van while they are hitched? Tamala Park, for example, asks you to unhitch caravans on the weighbridge, and the car and van each need their own certificate and fee.
2. Can you weigh one axle or one vehicle at a time? Banyule’s page notes its weighbridge “is not licensed to split weight”. Some bridges can weigh part of a rig; others record only whole loads.

If the answers are no, you can still do most of the audit. Weigh the car and the van separately, then measure the ball load with a tow ball scale, which Transport for NSW suggests for that reading. Mobile weighing services are another option. If you use a weighbridge, Transport for NSW says to confirm it is calibrated.

If it fails: without the right readings you are guessing at two or three limits, usually the ones closest to the line.

Step 7: Take five readings on the weighbridge

Each reading puts a different part of the rig on the bridge. Ask the operator to print or record each one, and keep the tickets.

1. Tow vehicle, hitched. Drive on until the car’s wheels are on the bridge and the van’s wheels are still off it. Transport for NSW says to weigh the fully packed vehicle, with its occupants, while the caravan is hitched.
2. Caravan axles, hitched. Drive forward until only the van’s wheels are on the bridge. This is the load through the van’s own tyres, the number to compare with GTM.
3. Caravan alone, unhitched. Unhitch with the whole van on the bridge, resting on its jockey wheel. NSW says ATM is measured this way. The WA guide says to keep the coupling at the height it sits when hitched.
4. Tow vehicle alone. Weigh the car with its load and occupants and no van.
5. Tow vehicle rear axle, hitched (optional). If the bridge can weigh one axle, hitch up again and weigh the car’s rear axle on its own.

A weight distribution hitch moves weight off the car’s rear axle, which changes readings 1, 2 and 5. Take every reading with it released first. If you tow with one, repeat readings 1, 2 and 5 with it tensioned the way you drive, and use the higher figure for each limit.

If it fails: a reading with a wheel on the edge of the bridge, or with the van’s jockey wheel too high or low, is wrong. Redo it rather than adjust the number in your head.

Step 8: Do the maths

Each limit compares one reading, or two added or subtracted, with the rating you wrote down.

The tow ball sum works because reading 1 is the car carrying the ball load and reading 4 is the same car without it. That is why the WA guide says tow hitch download “must be included as part of the tow vehicle GVM”. The GCM sum mirrors how the Australian Design Rules define GCM: the drawing vehicle’s mass plus the axle loads of the trailer behind it. These seven are the main limits, not the only ones: also check the tyre load ratings on the sidewalls, the rating stamped on the coupling, and, where your weighbridge can split the reading, the front axle.

Then check the tow ball load against the guides from Step 4, using the right basis for each. The WA guide’s 8 to 10 per cent is a share of the van’s ATM; NSW’s 5 to 10 per cent is a share of what the loaded van actually weighs (reading 3). The WA guide warns that a download above or below its range reduces stability, even when every limit passes.

Run the illustrative rig in our calculator below and two limits fail: the van is 58kg over its ATM and 18kg over its GTM. The tow vehicle passes its GVM with just 10kg spare. The van is overloaded, and the obvious fix, moving gear into the car, would push the car over instead.

If it fails: you are over a legal limit, so fix it before you drive. Take gear out, carry less water until you need it, or move weight only where both vehicles have room. Transport for NSW warns that you risk being fined, and that non-compliance is likely to affect your insurance; whether it does depends on the policy wording and the circumstances, so read your caravan insurance policy and your car’s.

Mistakes that fail the audit

• Weighing the van empty, or at the dealer. That is its tare, not what it weighs on the road.
• Reading ATM as the towing figure. ATM is what the van may weigh. Whether your car may tow it is a separate limit, and our payload guide covers the difference.
• Mixing up ATM and GTM. GTM leaves out the tow ball load, so it is measured hitched and is normally the smaller figure.
• Forgetting the ball weight lands on the car. A 250kg ball load is 250kg less for people and gear in the tow vehicle.
• Checking towing capacity and ignoring GCM. A car loaded to its GVM may not be allowed to tow its full rated capacity.
• Using a percentage instead of a scale. Ten per cent is a guide, not a measurement. Weigh the ball load.
• Treating fitted extras as tare. Anything added after the van was entered on the RAV comes out of your payload.
• Loading the car after the weighbridge. The esky, the firewood and the extra jerry can all count.
• Ignoring the tyres. Their load rating is a limit in its own right. Our touring tyre pressures guide covers the rest.
• Assuming any 50mm ball will do. Common 50mm balls are not rated beyond 3,500kg.

Put your readings into the audit

Enter the ratings from Steps 1 to 4 and the readings from Step 7. Each limit shows how much of it you are using, how many kilograms are spare or over, and a verdict. The example values are illustrative, built on Transport for NSW’s packing example.

If your rig is tight on GVM or GCM, read our guide to what a bigger budget buys in payload before you change vans. In NSW, a rated GCM over 4.5 tonnes also caps your towing speed at 100km/h.

Weigh it again whenever the load changes

A pass on the weighbridge is true for that load, on that day. Transport for NSW says to weigh the van each time you make a modification that adds weight, and to allow for weight you pick up along the way, from grey water to the cassette toilet. A new battery bank, a second spare or a bigger tow vehicle all change the answer.

So treat the audit as a habit, not a one-off. Weigh before the first big trip of each year, after any change to the van or the car, and whenever the packing list grows. Keep the tickets with the registration papers. The numbers that matter most are the ones nearest their limit, and those are the ones that move first.

Images: Callum Eddings, Alexander Schimmeck and Egor Myznik on Unsplash.