Towing Capacity Calculator
Check your tow vehicle's remaining capacity against GVM and GCM.
How the GVM and GCM check works
- GVM headroom = GVM − (kerb weight + people and gear + tow-ball download).
- GCM headroom = GCM − (loaded vehicle + the part of the caravan's weight carried by its own axles).
- Check both. A vehicle can be inside its GCM and still over its GVM, usually because of tow-ball download and a heavily loaded back seat or tray.
Result
Within GVM and GCM on these figures
- Loaded vehicle weight
- 2,950 kg
- GVM headroom
- 150 kg
- Combination weight
- 5,850 kg
- GCM headroom
- 150 kg
Tow-ball download is carried by the vehicle, so it counts towards GVM and is subtracted from the caravan's weight on its own axles.
How it's calculated
- Loaded vehicle = kerb weight + people and gear + tow-ball download.
- GVM headroom = GVM − loaded vehicle.
- Combination weight = loaded vehicle + (caravan ATM − tow-ball download).
- GCM headroom = GCM − combination weight. A negative headroom means you are over that limit.
Worked examples
Using the default figures
Loaded vehicle = 2,350 + 300 + 300 = 2,950 kg, so GVM headroom is 3,100 − 2,950 = 150 kg. Combination = 2,950 + (3,200 − 300) = 5,850 kg, so GCM headroom is 6,000 − 5,850 = 150 kg. Both are within their limits, but only just.
Terms explained
- GVM (Gross Vehicle Mass)
- The most the tow vehicle may weigh when fully loaded with passengers, fuel, gear and tow-ball download. It is set by the manufacturer and shown on the vehicle's compliance plate.
- GCM (Gross Combination Mass)
- The most the loaded tow vehicle and loaded caravan or trailer may weigh together while coupled.
- ATM (Aggregate Trailer Mass)
- The most the caravan or trailer may weigh when fully loaded and not coupled. It is stated on the trailer's compliance plate.
- Tow-ball download
- The downward force the coupling puts on the tow ball. The tow vehicle carries it, so it counts towards GVM, and it is subtracted from the caravan's weight on its own axles when working out GCM.
- Kerb weight
- The weight of the vehicle with fuel and fluids but without passengers or load. Your owner's manual or compliance documents give the figure.
- Braked towing capacity
- The most the manufacturer says the vehicle can tow with the trailer's brakes working. This calculator does not check it, so compare your caravan's ATM with it separately.
Assumptions and notes
- GVM, GCM and braked towing capacity must come from your vehicle's compliance plate or owner's manual.
- Manufacturer limits, state road rules and licence conditions still apply.
- Results are estimates only and are not financial, tax or legal advice.
Information last checked: August 2026.
Frequently asked questions
What is the difference between GVM and GCM?
GVM is the most your tow vehicle may weigh on its own, fully loaded. GCM is the most the loaded tow vehicle and loaded caravan may weigh together. You need to stay within both.
Does tow-ball download count towards GVM?
Yes. The tow vehicle carries the tow-ball download, so it is added to the vehicle's loaded weight when checking GVM.
Where do I find GVM, GCM and ATM?
GVM and GCM are on the tow vehicle's compliance plate or in its owner's manual, and ATM is on the caravan's compliance plate. Use the figures for your exact vehicle and van.