How the towing check works
A towing setup has to pass several separate limits. Passing one doesn't mean you pass the others. This calculator checks each of them, shows how much room you have left, and tells you the heaviest trailer your vehicle could pull as it's loaded today.
| Check | What is compared | Where the limit comes from |
|---|---|---|
| GVM | Loaded vehicle + towball download | Vehicle compliance plate or manual |
| GCM | Loaded vehicle + loaded trailer | Vehicle manufacturer |
| Towing capacity | Loaded trailer | Vehicle manufacturer (braked or unbraked) |
| Towball download | Weight on the towball | Vehicle manufacturer and towbar rating |
| Trailer ATM | Loaded trailer | Trailer compliance plate |
| Trailer GTM | Loaded trailer minus towball download | Trailer compliance plate |
NSW's rules say the loaded trailer must not weigh more than the lowest of the towbar rating, the vehicle's towing capacity, the trailer's own carrying capacity and the tyres' rated capacity. The same idea applies across Australia: the lowest limit is the one that counts.
Worked example
The example values loaded above describe a dual-cab ute rated to tow 3,500 kg, with a 3,200 kg GVM and a 6,000 kg GCM. It weighs 2,750 kg loaded and is towing a 2,800 kg caravan with 280 kg on the towball.
- GVM: 2,750 + 280 = 3,030 kg, under 3,200 kg with 170 kg spare.
- GCM: 2,750 + 2,800 = 5,550 kg, under 6,000 kg with 450 kg spare.
- Towing capacity: 2,800 kg, under 3,500 kg.
- Towball download: 280 kg, under 350 kg. That's 10% of the caravan's weight.
Everything passes, but notice the GCM. With this vehicle at 2,750 kg, the heaviest trailer it can pull is 6,000 − 2,750 = 3,250 kg, not the 3,500 kg on the brochure. Our how much can I tow calculator works that out for you, and the guide to why a 3,500 kg rating often isn't 3,500 kg explains why.
Why the towball download is counted twice (but isn't)
The towball download is part of the trailer's weight, but once you hitch up it presses down on the vehicle. So it uses up the vehicle's GVM. For the GCM it doesn't matter where the weight sits, because the vehicle and the trailer are added together. That's why the GCM check adds the vehicle and trailer weighed separately, without adding the towball download again.
Common questions
- What is the difference between towing capacity and GCM?
- Towing capacity is the most the trailer itself may weigh. GCM (gross combination mass) is the most the vehicle and trailer may weigh together. You have to stay under both, so a heavily loaded vehicle can reduce the trailer you can tow below its towing capacity.
- Does towball download count towards GVM?
- Yes. Once the trailer is hitched, the towball download sits on the vehicle, so the loaded vehicle plus the towball download must be under the GVM.
- Which trailer weight do I enter, ATM or tare?
- Enter what the trailer weighs loaded as you travel, measured on its own. That is its actual ATM. The ATM on the trailer's plate is the most it is allowed to weigh, which this calculator checks as an optional extra.
- Is it legal to tow at exactly the limit?
- Being at a limit is not over it, but it leaves no room for error. Weights change with fuel, water and shopping, and a weighbridge reading can differ from the numbers you planned with, so most people leave a margin.
- Where do I find my vehicle's GVM and GCM?
- On the compliance or VIN plate (often in the driver's door opening), in the owner's manual, or from the manufacturer's specifications for your exact model and variant. Figures can differ between variants of the same model.
Sources
- Towing a trailer or caravan, NSW Government (Transport for NSW)
- Vehicle Standards Bulletin 1 (Revision 6): trailers with an ATM of 4.5 tonnes or less (August 2026), Australian Government, Department of Infrastructure
- How much is your vehicle designed to carry or tow?, NRMA
Rules checked against these sources on 12 October 2026. See rules, sources and method.