How to read weight figures and examples
- Ratings are maximum limits, not measurements of your loaded setup. Confirm the exact variant and approved ratings.
- Measure loaded coupling weight. A percentage or the difference between ATM and GTM ratings does not establish today's coupling weight.
- An added load changes both axle reactions according to its position. A change is not a total axle load; use measured starting axle weights and add each load once.
- Combination mass is unhitched loaded vehicle plus total loaded trailer, or the sum of all coupled axle readings. Count coupling mass once.
- Examples and AI suggestions are planning aids, not verified measurements or compliance clearance. Unknown figures require measurement; active weight-distribution hitches and gooseneck arrangements need their own assessment.
Introduction
If you own a vehicle in Australia and plan to tow anything — a caravan, camper trailer, boat or horse float — you need to understand three weight figures that are printed on your compliance plate and vehicle registration documents. They are:
These three numbers interact with each other, and getting any of them wrong can put you outside your legal limits without obvious warning. This guide explains each one in plain Australian English with worked examples.
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What Is GVM (Gross Vehicle Mass)
GVM is the maximum legal weight of your vehicle when fully loaded with fuel, fluids, accessories, passengers, cargo and gear. It is set by the vehicle manufacturer and shown on the compliance plate (usually in the engine bay or door jamb).
**Where to find it:** Compliance plate, vehicle registration document, or the manufacturer's specification sheet. In some states it is labelled as "RM" (Registered Mass).
**Why it matters:** Every kilogram you add to the vehicle — a bullbar, water tanks, passengers, gear — counts against GVM. Exceeding GVM puts you outside your legal registration, which can affect your vehicle insurance, your driver licence class requirements and your vehicle's roadworthiness status.
Illustrative Example
Fictional example: a 3,350 kg GVM and 2,415 kg unhitched starting mass leave 935 kg. Fuel and equipment included in the starting mass are not added again. That 935kg must cover:
For many owners, the 935kg is fully consumed before they even consider the trailer's tow rating. This is the most common way people end up outside GVM without realising it.
> **Safety caveat:** GVM is a permitted maximum loaded mass, not a standard vehicle mass or fuel assumption. Net accessories and carried loads affect actual mass. Measure the travel setup with an appropriate weighbridge or calibrated scales and compare all applicable limits.
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What Is GCM (Gross Combination Mass)
GCM is the maximum legal combined weight of your vehicle and the trailer when coupled together. It is shown on the compliance plate and registration documents.
The formula is simple:
**Actual combined mass = unhitched loaded vehicle mass + total loaded trailer mass**, or **coupled vehicle axle masses + trailer axle masses**. Count coupling load once; compare the total with the GCM rating.
If your unhitched loaded vehicle is 2,900 kg and the complete loaded trailer is 2,100 kg, the combination is 5,000 kg. If your GCM rating is 5,300kg, you have 300kg of headroom. If your GCM is 4,800kg, you are 200kg over.
**Why it matters:** GCM governs the total combined weight of the towing system. It is often the first limit exceeded when people add accessories to the vehicle and load the caravan at the same time — even when the tow rating has not been reached.
Illustrative Example
A vehicle with GCM of 5,995kg, kerb weight of 2,387kg, and towing a caravan with an ATM (Aggregate Trailer Mass) of 2,400kg:
That looks like plenty of room. But if the same owner adds another 200kg of accessories to the vehicle and fills the caravan to ATM (2,400kg), the combination is now 5,387kg — still within GCM but now within 700kg of the limit. Add another accessory or a heavier trailer and the headroom disappears quickly.
> **Safety caveat:** GCM limits are enforced by state road authorities. Exceeding GCM is a breach of your vehicle's registered operating conditions. This affects your insurance and may require a different registration category.
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What Is Payload
Payload is the weight you can add to the vehicle before reaching GVM. It is not a separate registration figure — it is a calculation:
**Remaining GVM capacity = GVM rating − actual vehicle mass**. Published payload depends on the manufacturer's defined starting mass; tare and kerb are not interchangeable.
Confirm the exact manufacturer's kerb/tare definition, including fuel and standard equipment. Actual fitted options can change the starting mass; a plate may show ratings without actual axle masses.
Payload is the number that controls what you can actually carry — passengers, fuel, water, accessories, cargo and tow ball mass. Every one of these items reduces the available payload.
Illustrative Example
Fictional example: a 3,165 kg GVM and 2,387 kg starting mass leave 778 kg. If the owner adds:
Total additions: 455 kg. Remaining GVM capacity: 323 kg. A further 25 kg rack, 30 kg water and 70 kg passenger use 125 kg, leaving 198 kg. Any other gear reduces that margin; these totals do not establish axle compliance.
> **Safety caveat:** Payload is often the first limit exceeded before GVM, GCM and tow rating. It is also the easiest to miss because it is a calculated figure, not a printed one. Use our free Vehicle Checker to calculate your payload and see how accessories affect it.
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How These Three Numbers Interact
The three limits operate simultaneously. You can be within your tow rating and still exceed GVM. You can be within GVM and still exceed GCM. You can be within all three and still exceed an individual axle load rating.
The practical approach is:
1. **Start with payload.** Calculate your available payload and list everything you plan to carry. This is the most common way to run into trouble.
2. **Check GVM.** Ensure your loaded vehicle weight is within GVM.
3. **Check GCM.** Add your trailer loaded weight and ensure the combination is within GCM.
4. **Check axle load ratings.** The front and rear axle ratings operate independently of GVM — heavy accessories on the front can exceed the front axle while the vehicle is still under GVM.
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Where to Find Your Vehicle's Numbers
If you cannot find any of these, use our free Vehicle Checker tool, which has manufacturer specifications for many popular Australian tow vehicles.
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Sources and Review Method
The weight terminology used in this guide follows:
ClearPath does not verify individual compliance plate figures. Vehicle owners should always confirm weight figures against their own compliance plate and registration documents.
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What Next
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