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Caravan weights explained
ATM, GTM, GVM, GCM, tare, payload and ball weight. What each one means, and the subtraction that catches people out.
Every buyer hits this and almost nobody is given a straight answer. Here is the whole thing in one page: what each term means, where the numbers hide, and the calculation that catches out more caravan buyers in Australia than anything else.
The words, in plain English
| Term | What it means | Where to find it |
|---|---|---|
| Tare | The van as it left the factory, empty. Check what the manufacturer included, gas bottles and water are treated inconsistently. | Compliance plate |
| ATM | Aggregate Trailer Mass. The maximum the loaded van may weigh when it is not coupled. Includes ball weight. | Compliance plate |
| GTM | Gross Trailer Mass. The maximum that may sit on the van’s own axles when it is coupled. ATM minus ball weight. | Compliance plate |
| Payload | ATM minus tare. Everything you own, eat, drink and carry. | Calculate it yourself |
| Ball weight | Downward mass on the tow ball. Commonly 8 to 12% of ATM on off-road vans. | Weigh it, do not trust the brochure |
| GVM | Gross Vehicle Mass. Maximum loaded weight of your tow vehicle alone, including the ball weight pressing down on it. | Vehicle placard |
| GCM | Gross Combination Mass. Maximum for vehicle and van together. | Vehicle placard |
The GCM trap
Your vehicle has a GVM and a maximum braked towing capacity. Add them together and you will usually get a number larger than the GCM. That is not a misprint, it means you cannot legally use both maximums at once.
A common dual-cab: GVM 3,050 kg. Braked towing capacity 3,500 kg. Added together, 6,550 kg. But the GCM is 6,000 kg. So if you tow a van loaded to its full 3,500 kg ATM, your vehicle may only weigh 2,500 kg, roughly its kerb weight before you add passengers, fuel, a bullbar, drawers, a fridge, or the 350 kg of ball weight the van puts on your towbar. The shortfall is 550 kg. That is not a rounding error.
The payload trap
Manufacturers advertise ATM because it is a big number. Payload is the number that governs your life. A van with a 3,500 kg ATM and a 2,900 kg tare gives you 600 kg. That sounds generous until you start filling it:
| Item | Realistic weight |
|---|---|
| Fresh water, 180 L | 180 kg |
| Two full gas bottles (9 kg) | 38 kg |
| Food, clothing, bedding, kitchen for two | 90 to 130 kg |
| Tools, recovery gear, spares, second spare wheel | 60 to 100 kg |
| Generator or extra battery | 20 to 40 kg |
| Awning walls, mats, chairs, table, camp kitchen | 40 to 70 kg |
| E-bikes or similar, if carried | 50 to 80 kg |
| Typical total | 478 to 638 kg |
Water is the surprise. It is the heaviest single thing you carry, and the more remote you go the more of it you need. A van marketed for extended off-grid travel with only 400 kg of payload is quietly telling you it does not expect you to fill its tanks and load it at the same time.
Ball weight, and why the brochure figure misleads
Ball weight is the downward force the drawbar puts on your tow ball. It is carried by the vehicle, not the van, so it consumes your GVM, not your ATM. Commonly 8 to 12 per cent of ATM on an off-road van.
Published figures are almost always measured at tare, on an empty van. Loaded with water and gear it climbs, sometimes considerably. Many dual-cabs rated to tow 3,500 kg cap tow ball download at 350 kg, so a heavy van loaded to 10 per cent can sit within a few kilograms of the vehicle’s limit.
Any dealer can tell you the brochure number. Ask what it weighs loaded, and whether they have actually put it on a scale. The answer tells you something either way.
What to actually do about it
- Get the rig weighed loaded, at a public weighbridge, before your first big trip. Four corners if you can, side-to-side imbalance is common and rarely suspected.
- Treat any payload under 500 kg on a full off-road van as a serious question, not a detail.
- Ask whether the tare on the plate is for that exact van or a representative model. An option-heavy build can be 150 kg heavier than the brochure.
- Do the GCM subtraction before you fall in love with anything: GCM minus the van’s ATM equals the most your loaded vehicle may weigh.
Disclaimer. General information only. Always verify weights and specifications against the compliance plate of the actual van and the placard of your actual vehicle, and have any loaded rig weighed at a public weighbridge before travelling.
