Caravan ATM, GTM, GVM and GCM Explained in Plain Australian English

Caravan weight jargon makes a lot more sense once you split it into two groups: ratings (the maximums set by the manufacturer) and measured weights (what your rig actually weighs when you put it on a scale).

Having your setup weighed while travelling is becoming a normal scenario nowadays. Much better to know your weights before you leave rather than get caught 400 kilos overweight 1,500km from home. There are plenty of mobile weighing businesses around nowadays that can come to your home or meet you at the local supermarket car park. My advice is spend a few bucks to have peace of mind and remain safe towing.

The four ratings you'll run into

• ATM (Aggregate Trailer Mass) — the max your loaded caravan is allowed to weigh, including what it pushes down on the tow ball, measured with the van sitting on its own.
• GTM (Gross Trailer Mass) — the max weight allowed through the caravan's own wheels once it's hooked up to the car.
• GVM (Gross Vehicle Mass) — the max loaded weight your tow vehicle is allowed to be.
• GCM (Gross Combination Mass) — where it's specified, the max combined weight of the car and van together.

There's no such thing as "a caravan's weight"

An ad showing tare weight tells you almost nothing about whether your loaded, packed-for-travel van is within its limits. Don't use an average weight or "what my mate's similar van weighs" — get the actual figures for your actual van.

Don't double up the tow ball weight

When you weigh the car and van hooked up together, the tow ball weight is already included in what's sitting on the car's tyres — don't add it again on top. This trips a lot of people up.

Tare isn't your travelling weight either

Tare weight often doesn't include water, gas, food, your gear or accessories fitted after the van left the factory. The only way to know your real payload margin is to weigh your van as you'd actually travel.

Six things to check, not just one

1. Your loaded caravan is within ATM.
2. The weight through the caravan's wheels is within GTM.
3. Your loaded tow vehicle is within GVM.
4. Each axle — car and van — is within its own rating.
5. Your actual tow ball weight and coupling gear are within their ratings.
6. The whole combination is within GCM and your manufacturer's towing limits.

Whichever of these has the least room left is the one that actually controls what you can and can't do — an advertised "3,500kg tow capacity" doesn't mean anything if your GVM, axles or GCM run out first.

Keep the paperwork handy

Grab the caravan's compliance plate, your vehicle's plate, the owner's manuals, tyre ratings, and your towbar and coupling ratings, plus your actual weighbridge results. Note who and what was on board when you weighed it — without that context, a weight ticket doesn't mean much on its own.

Safety boundary: General Australian information only. Definitions and requirements can change and manufacturer conditions differ. Confirm the current rules, vehicle and component ratings, and get qualified engineering or other professional advice for your combination.

Follow the full sequence in the Caravan Weights & Towing hub: understand the ratings, estimate the load, then verify actual measurements.