Tips on understanding ATM & GTM weights

Knowing about your caravan weights is fundamental to caravanning, as there are legal requirements about the weight capacity of your towing vehicle and caravan. CIA Victoria has some handy tips and hints to help you understand the ATM and GTM weights specified on your vehicle plate and how to make your tow setup safe and legal.

In essence, the ATM and GTM weights specified on your vehicle plate are the maximum capacity that your caravan can be filled up to. Aggregate Trailer Mass or ATM refers to the total maximum permitted mass of the caravan (the weight on your tyres and on your tow ball) when carrying its maximum payload, including fluids, luggage and personal effects.  Gross Trailer Mass or GTM refers to the maximum mass that can be transmitted to the ground by the axle or axles of the caravan when coupled to a drawing vehicle (purely the weight on your tyres) when carrying its maximum payload including fluids, luggage and personal effects.

You can work out your allowable payload by deducting the ‘Tare Mass’ from the ‘ATM’. Your payload refers to the maximum load specified by the original caravan manufacturer permitted for your belongings and items in the caravan including fluids, luggage, personal effects and any aftermarket fittings/equipment. Remember that your Tare Mass is the weight specified by the original manufacturer for the total weight of the caravan (load on tyres as well as the tow ball) when it is empty, so if you fit some aftermarket items your tare weight is going to increase, which means your payload is actually decreasing.

Make sure you don’t exceed your caravan weights because if you do have an accident you’re not going to be insured. Therefore it is important to make sure you understand your caravans weight. For more tips like this one, head over to