GarageCalc ATM: Aggregate Trailer Mass (the caravan)
ATM is the maximum your caravan may weigh when fully loaded and sitting on its own jockey wheel, unhitched. It is set by the manufacturer and stamped on the compliance plate. It includes everything: the van itself, water, gas, batteries, food, gear, the lot. The gap between the van's tare (empty weight) and its ATM is your payload, and it is usually much smaller than owners expect. Run yours through the caravan weight calculator.
GVM: Gross Vehicle Mass (the car)
GVM is the maximum your tow vehicle may weigh loaded: the car, fuel, driver, passengers, luggage, accessories like a bull bar or canopy, and critically, the ball weight pressing down from the caravan. That last part is what catches people out. A 350 kg ball weight is 350 kg of your car's payload, gone before anyone gets in.
How they interact: a worked example
Take a popular combination: a wagon with a 3,280 kg GVM and a 3,500 kg braked rating, towing a van with a 3,000 kg ATM and 300 kg on the ball.
- ATM check: 3,000 kg van against a 3,500 kg braked rating. Passes with room.
- GVM check: if the car weighs 2,600 kg empty, add 300 kg ball weight and you are at 2,900 kg before people or gear. That leaves 380 kg for four adults and their bags. Tight.
- The trap: the towing rating said "easily". The GVM said "barely". Both are right, they measure different things.
That is why the braked rating in the brochure is never the whole story. Check all four limits, ATM, ball weight, GVM and GCM, at once with the caravan towing calculator.
Quick reference
| Term | Belongs to | Means | Where to find it |
|---|---|---|---|
| ATM | Caravan | Max loaded mass, unhitched | Caravan compliance plate |
| GTM | Caravan | Max mass on the van's axles when hitched (ATM minus ball weight) | Caravan compliance plate |
| GVM | Car | Max loaded mass of the car, ball weight included | Car placard, owner's manual |
| GCM | Car | Max mass of car and caravan together | Owner's manual, our vehicle pages |
Frequently asked questions
Is ATM the same as towing capacity?
No. ATM is a property of the caravan (its maximum loaded mass). Towing capacity, or the braked rating, is a property of the car. A legal match needs the caravan's ATM to be at or under the car's braked rating. They are compared to each other but they describe different vehicles.
Does the caravan's weight count toward my car's GVM?
Only the ball weight does. GVM is the loaded car, and the part of the caravan that rests on the tow ball (typically 8 to 12 percent of the van) is carried by the car, so it counts. The rest of the van rides on its own axles and counts toward GCM instead.
Where do I find ATM and GVM?
ATM is on the caravan's compliance plate, usually near the drawbar or inside a hatch. GVM is on the car's compliance or tyre placard, typically the driver's door jamb, and in the owner's manual.