How to Calculate GCM Weight

How to Calculate GCM Weight – 3 Options!

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When you first decide to hitch up a caravan or camper to the back of your car, it seems rather simple right? Find out how much your vehicle can tow (towing capacity) and make sure you don’t go over it.

In reality, towing weights are much more involved than that and knowing what all of the terms mean in relation to your set-up is vital.

Here we cover everything you need to know about GCM weight.

To understand all of the towing weights, check out our simple guide to towing weights.

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What is GCM Weight?

Gross Combination Mass (GCM) is the maximum allowable weight of your car and caravan combined, which is set by the manufacturer of your vehicle.

In other words, GCM is the weight of both the car and the caravan together when they’re hitched up.

GCM = Maximum Allowable Weight of Car + Caravan

What Does GCM Weight Include?

As GCM is the combined weight of both the fully loaded car plus the fully loaded caravan added together, this figure includes absolutely everything.

Gross Combination Mass (GCM)

GCM Weight Includes:

  • Driver & passengers in the car
  • Fuel tank contents
  • Water tank contents
  • Waste tank contents (black water, grey water & toilet cassette)
  • Hot water system contents
  • Full gas bottles
  • Food & drinks
  • Clothing
  • Linen
  • Cooking gear
  • Toys, bikes, scooters, games, books etc.
  • Personal luggage (electronics, toiletries etc.)
  • Camping furniture (chairs & tables)
  • BBQ
  • Jerry cans & holders
  • Tools, toolboxes & maintenance gear
  • Hoses & leads
  • Levellers & chocks
  • Annex walls/ privacy screens
  • Outdoor matting
  • Accessories
  • Upgrades (solar system, additional water tanks/ fuel tanks etc.)
  • Modifications
  • Tow ball weight

… and anything else that is added to the car and caravan either temporarily or permanently.


Does GCM Include Tow Ball Weight?

Caravan Tow Ball

Yes, GCM definitely includes the tow ball weight.

However, be careful when you’re working out your GCM that you don’t accidentally add the tow ball weight in twice.

If you’re adding the weight of the fully loaded car to the weight of the fully loaded caravan, you need to make sure that either the car or the caravan has the tow ball weight accounted for, not both.

Alternatively, you could just weigh the entire set-up as one complete unit, then you won’t have to worry about which piece needs to have the tow ball weight added to (or subtracted from).

3 Ways to Measure Tow Ball Weight →

Sound confusing?

It’s actually quite easy once you know how to calculate GCM weight. Let’s delve into it!

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How to Calculate GCM Weight

There are three different ways you can calculate GCM weight. I’ll start with the easiest one, then move onto the other options.

You’ll need to use a Public Weighbridge to get the various weights of your set-up. Weighbridges are usually found at local council rubbish and recycling facilities.

Weighbridge scales are designed for the length and weight of trucks, so you won’t have to worry about whether or not your caravan set-up will fit on.

It’s always helpful to tell the staff in the booth that you need to work out your caravan weights, that way they’ll know that it may take you a couple of minutes. Another tip is to wait off to the side until the weighbridge is clear of trucks who need to move through quickly, allowing yourself the time you need to get your weights without feeling super rushed.

OPTION 1: Weigh the Combined Set-up

How to Weigh a Caravan - GCM

How to Weigh the Combined Set-up

  1. Ensure the vehicle and caravan are both fully loaded with luggage, passengers, food, fuel, water, gear etc.
  2. Drive the vehicle and caravan onto the weighbridge
  3. Record the weight
  4. This needs to be lower than the manufacturer stated GCM

OPTION 2: Fully Loaded Vehicle + ATM

How to Calculate GCM Weight

OPTION 2: Fully Loaded Vehicle + ATM

  1. Measure the weight of your fully loaded vehicle (unhitched from caravan)
  2. Measure your ATM (fully loaded caravan, unhitched from vehicle)
  3. Add the 2 weights together

* In this scenario the caravan carries the tow ball weight


OPTION 3: GVM + GTM

How to Calculate GCM Weight

OPTION 2: GVM + GTM

  1. Measure your GVM (fully loaded vehicle, hitched up to caravan)
  2. Measure your GTM (fully loaded caravan, hitched up to vehicle)
  3. Add the 2 weights together

* In this scenario the vehicle carries the tow ball weight

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What to Do if You’re Over Your GCM

Organisational boxes (caravan pantry)
Pull out as much as you can to reduce your GCM weight

Once you’ve calculated your GCM you might find that it’s over the manufacturer specified figure. If that’s the case, you will need to do what you can to reduce your figures until they fall under the required GCM.

In general, this means removing weight from the car and/ or caravan until you can get it down to the weight that you need it to be.

If you’re not sure where to take the weight from, you can weigh the car and the caravan individually and check to see if it’s one (or both) of those that is overweight and pushing your above your limit.

Below is a useful calculator to help you work out where you’re overweight.

Towing Weight Calculator →

It’s very common for full caravan water tanks to push set-ups over their weight allowances, so you could start there.

However, if travelling with empty water tanks is not an option for you, then it’s time to start culling your gear.

For the caravan or camper, think food, clothing, linen, camping gear, toys, books etc. When it comes to the car, consider reducing your tools, accessories and any unnecessary luggage.

Although there will always be some essential items, we really don’t need as much as we think on the road. Making sure that your set-up is within its towing limits keeps you legal, insured and most importantly, safe.

The Caravan Packing List (below), is a handy resource to help with tracking and organising payload.

Caravan Packing List

Caravan Packing List

Never forget a thing with the ULTIMATE Caravan Packing List!

  • Pre-filled with 600+ items
  • 17 categories
  • ‘Weight’ column (to organise payload)
  • PRINTABLE – fully customisable
  • DIGITAL – completely interactive
  • Download once, use it over-and-over
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GCM Weight FAQs

What is GCM for my vehicle?

GCM stands for Gross Combined Mass, which means it’s the combined weight of both the tow vehicle and trailer added together.

What is GCM in Australia?

GCM (Gross Combined Mass) in Australia relates to any vehicle that is towing a trailer or caravan and is the combined weight of the entire set-up.

How do you calculate GCM on a caravan?

GCM = GVM (fully loaded vehicle, unhitched) + ATM (fully loaded caravan, unhitched)

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