Towing Capacity Calculator
Whether a load is legal against your vehicle's limits — payload, tow ball weight and combined mass.
Four limits apply at once and all must be satisfied.
How the towing capacity calculator works
Four limits apply at once and all must be satisfied. Payload is what the vehicle itself can carry. Braked towing capacity limits the trailer. Gross combination mass caps the two together — and this is the one people miss, because a vehicle at maximum payload often cannot also tow its maximum trailer.
Tow ball download counts against payload, not against towing capacity. A 3,500 kg caravan with 10% ball weight puts 350 kg into the car before any passengers or luggage, which is most of a family car's payload before anyone gets in.
Every figure comes from your own vehicle's compliance plate. These vary between variants of the same model, and the placard is authoritative.
Formula: GCM check: kerb + payload used + trailer ≤ GCM
Worked examples
| Inputs | Legal? | Note |
|---|---|---|
| A 2.8 t van behind a large 4WD | Yes — within all four limits | legal, but tight on payload |
| At maximum trailer | No — combined mass exceeds GCM by 370 kg | GCM exceeded |
| Light trailer, loaded car | Yes — within all four limits | payload is the binding limit |
FAQFrequently asked questions
What is GCM?
Gross combination mass — the maximum for vehicle and trailer together. It is usually less than GVM plus towing capacity, which is what catches people out.
Does tow ball weight count against towing capacity?
No — against payload. A 350 kg ball weight uses 350 kg of what the car can carry before any passengers.
Why can I not tow the maximum with a full car?
Because GCM caps the total. Maximum payload and maximum trailer together usually exceed it.
What tow ball download should I have?
Typically 10% of trailer mass, within the range the manufacturer specifies. Too little causes sway; too much overloads the rear axle.
Where do I find these numbers?
The compliance plate or placard on your vehicle. They differ between variants of the same model, and the placard is authoritative.
Where these figures come from
- ISO 4000 / ETRTO — tyre designation and dimensions — the width / aspect ratio / rim marking this page decodes
- Australian Government — Green Vehicle Guide — the official Australian fuel consumption database
Last checked: September 2026. Tyre dimensions follow the ISO metric marking standard; engine formulas are the standard textbook forms.