Caravan Weight Calculator (Australia): ATM, GTM, TBM, GVM & GCM
Check your caravan and tow vehicle against every plated limit used in Australia.
Example rig — replace every number with your own.
Towing weight check
Limited by Trailer vs towing capacity
assumes tow ball mass = 10 % of the trailer
Uses the numbers you enter from your plates and manuals — it can't check them for you. Weigh your loaded rig at a public weighbridge or CAT scale. Rules vary by state and country. Not legal advice.
Your caravan's loaded weight (ATM, uncoupled) must not exceed its ATM plate or the lower of your vehicle's towing capacity and towbar rating. The tow ball mass is carried by the vehicle, so vehicle + TBM must stay under GVM, and vehicle + caravan must stay under GCM.
How it's calculated
• GTM actual = laden ATM − tow ball mass (TBM)
• Vehicle coupled = uncoupled vehicle laden + tow ball mass
• Combined weight = vehicle coupled + GTM actual
• Towing capacity = lesser of vehicle maker's towing capacity (braked/unbraked) and towbar rating
• Largest trailer ATM = lowest of towing capacity, towbar/vehicle ball limit ÷ assumed %, (GVM − vehicle) ÷ assumed %, and GCM − vehicle
Frequently Asked Questions (FAQ)
What is the difference between ATM and GTM?
ATM (aggregate trailer mass) is the loaded trailer's total weight when not coupled. GTM (gross trailer mass) is the weight on the trailer's own axles when coupled — the tow ball mass has moved onto the car, so GTM is always less than ATM (RACQ).
What is GCM?
Gross combination mass: the maximum the vehicle and trailer may weigh together, as set by the vehicle maker. It can be less than GVM plus towing capacity (WA Department of Transport guide).
Do towbar ratings matter if my car can tow 3,500 kg?
Yes. RACQ: the maximum is the lesser of the vehicle maker's towing capacity and the towbar rating.
What is the unbraked limit?
Your vehicle manual lists it; it cannot exceed 750 kg in Australia.
Sources
- RACQ — What you need to know about trailer and tow vehicle specifications
ATM, GTM, payload, ball load, towbar rating overrides, max towable = lesser of vehicle and towbar
- WA Department of Transport — Safe Towing Guide (PDF)
ATM, GTM, GVM (incl. hitch download), GCM, unbraked 750 kg, tow hitch download ≈ 8–10 % of ATM
- 4X4 Australia — Towing vehicle weights explained
Secondary source: tare vs kerb definitions
Last reviewed: 2026-10-26
Built and maintained by Numberwright. The checks follow the definitions published by motoring bodies, transport departments and vehicle makers listed under Sources. Found a mistake? Contact details coming soon.
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