GarageCalc 
An illustrative payload budget
Assume a 2,200 kg starting tare and 2,800 kg ATM: the difference is 600 kg. Adding an assumed 190 kg of water, 18 kg of additional gas mass and 150 kg of gear uses 358 kg, leaving an estimated 242 kg against ATM. These are fictional inputs, not typical weights or a complete packing list. Empty cylinders, batteries and fitted equipment may already be included in your starting mass.
Compare your actual loaded trailer and vehicle with the matching ratings using the caravan towing calculator. Definitions: Transport WA mass definitions. Equipment and loading requirements: NSW towing guidance. Checked October 25, 2026.
How it's calculated
Frequently asked questions
What is the difference between tare, ATM and GTM?
Use the trailer plate and build documents to establish its tare and which equipment it includes. ATM limits the entire loaded trailer mass. GTM is a separate rated limit for the mass carried by its axles when coupled. Do not infer a missing GTM rating from a measured ball load.
Does water count toward payload?
Yes. For this estimate, one litre of added water is approximated as one kilogram. For example, an assumed 190 litres adds about 190 kg. Add only water and other loads not already included in the starting tare or measured base mass.
What ball weight should I aim for?
Use the trailer and vehicle manufacturers' loading instructions and the applicable equipment limits. This calculator displays a ratio, not a stability verdict. Measure the packed trailer and check axle loads as well as the ball load.
What if the estimate exceeds ATM?
Reduce the load and obtain loaded measurements before towing. This arithmetic cannot approve a modification or change a plate rating. Check any proposed rating change with the manufacturer and the relevant registration authority.