TowReadyAggregate Trailer Mass
The maximum permitted mass of a fully loaded trailer, including the load carried through the coupling. Compare this rating with the whole loaded trailer weight, measured unhitched.
Make sense of the numbers.
Start with the plates and manuals. Finish with real measurements.
Gross Trailer Mass
The maximum permitted mass supported by the trailer wheels when loaded and hitched. Actual axle-supported trailer mass is the whole trailer mass minus its ball load. This calculator does not check the GTM rating.
Gross Vehicle Mass
The maximum permitted loaded vehicle mass. People, fuel, accessories, luggage and the trailer’s ball load all use this allowance.
Gross Combination Mass
The maximum permitted mass of the loaded towing vehicle and trailer together. Add the vehicle’s loaded mass before hitching to the whole trailer mass. Do not add ball load again.
Towball download
The downward load at the coupling. Use a measured value and the lowest applicable vehicle, towbar and coupling ball-load limit. Follow manufacturer guidance for load distribution; there is no universal percentage that suits every rig.
Payload allowance
A rating minus a compatible empty-mass figure. Vehicle kerb definitions and trailer tare figures vary. Check what fuel, water, accessories and equipment those figures include.
How the weights fit together
For a vehicle weighing 2,500 kg before hitching, a 2,500 kg loaded caravan and a measured 250 kg ball load: the hitched vehicle mass is 2,750 kg, the combined mass is 5,000 kg, and the mass supported by the trailer wheels is approximately 2,250 kg.
Measure your travel-ready rig
Load the people, fuel, water, food and equipment you intend to take. Use a suitable weighbridge and a measured coupling load. Follow the weighbridge operator’s procedure and your manufacturer’s instructions. Recheck after changing your load.
Weight is only one part of towing
Axle loads, GTM, tyres, brakes, hitch equipment, load distribution, dimensions and local road rules also matter. A result within the calculator’s limits does not establish that your rig is safe or legally compliant.
Read NSW Government towing guidance and check your own state or territory authority and manufacturer documentation.
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