How Much Weight Can A Roof Box Hold?
How much weight a roof box can hold depends on the roof box, roof bars and vehicle it is being used with. There isn't one weight limit that applies to every roof box setup, and the amount of empty space inside the box does not determine how much weight you can safely put into it.
Before loading a roof box, you need to consider several limits together: the maximum load specified for the box, the capacity of the roof bars and, crucially, the maximum permitted roof load for your vehicle.
The safest rule is simple: never exceed the lowest applicable limit for your particular setup.
Litres and Kilograms Tell You Two Different Things
This is an important distinction when choosing and packing a roof box.
Roof box capacity is normally expressed in litres. For example, our Large roof box provides around 470 litres of additional storage, while our Extra Large option provides around 580 litres.
Those figures tell you about volume, not permitted weight.
A 580-litre box can physically accommodate a considerable amount of luggage, but that doesn't mean you can fill every available litre with heavy objects. Depending on what you're carrying, you could reach the applicable weight limit while there is still plenty of empty space inside.
If your main question is about physical luggage capacity rather than weight, see How Much Can You Put in a Roof Box?.
Your Car Has a Maximum Roof Load Too
The roof box is only one component of the system. Your vehicle manufacturer specifies how much weight can be carried on the roof, and that limit needs to be respected.
Importantly, the vehicle's roof load isn't necessarily just the luggage you've put inside the box.
The complete roof load can include:
- The roof box itself.
- The roof bars and relevant mounting equipment.
- The luggage and other contents carried inside the box.
Check the vehicle manufacturer's documentation for the applicable roof-load specification for your particular model. Don't assume that another car from the same manufacturer has an identical limit.
The Roof Bars Have a Limit as Well
Roof bars form the connection between the vehicle and roof box, so their permitted load also matters.
If you're using Roof Bar Hire from Midlands Roof Box Hire, we'll establish a suitable compatible setup for your vehicle. Our guide How Do Roof Boxes Attach To Cars? explains more about the relationship between the vehicle, bars and box.
Customers without obvious raised rails shouldn't assume this prevents them from hiring either. Different vehicles use different mounting systems, as explained in Can I fit a roof box to a car with no rails?.
Which Weight Limit Should I Follow?
You need to comply with all the limits applying to your particular setup, which effectively means that the lowest relevant limit becomes the constraint you cannot exceed.
For example, having a roof box capable of carrying a particular load doesn't override a lower limit imposed by the vehicle or supporting equipment.
Equally, a vehicle with a relatively generous permitted roof load doesn't mean you can exceed the specified limits of the box or bars fitted to it.
Think of the system as a chain. The strongest component doesn't cancel out the limitations of another component.
Don't Forget the Weight of the Roof Box and Bars
This is where people can make an easy calculation error.
If you're checking your vehicle's maximum permitted roof load, you cannot necessarily allocate that entire figure to holiday luggage. The equipment installed on the roof has weight of its own.
The box, bars and relevant mounting components therefore need to be accounted for when determining how much additional luggage can be carried without exceeding the vehicle manufacturer's limit.
Always use the specifications applicable to the actual equipment and vehicle rather than estimating.
Should Heavy Items Go in a Roof Box?
Just because an object physically fits inside a roof box doesn't automatically make the roof the best place to carry it.
Roof boxes are particularly useful for suitable bulky and relatively lightweight luggage. Where appropriate, dense and particularly heavy belongings may be better carried securely and low down inside the vehicle, subject to the vehicle manufacturer's guidance and its other loading limits.
For a family holiday, the roof box might be useful for suitable clothing bags, coats and other bulky travel equipment, freeing up boot space for denser items.
This approach can make good use of the available roof-box volume without unnecessarily concentrating heavy loads high on the vehicle.
Spread the Weight Rather Than Creating One Heavy End
Staying below the overall weight limit isn't the only consideration. How you arrange that weight matters too.
Avoid putting all the heavier suitable luggage at one end of the roof box. Contents should be distributed appropriately and secured so that they cannot freely move around when the vehicle accelerates, brakes or changes direction.
How Do You Pack a Roof Box Properly? covers sensible loading and luggage organisation in considerably more detail.
Can You Overload a Roof Box Without Filling It?
Yes, and that's precisely why looking at the remaining space isn't a reliable loading method.
Imagine filling a roof box with a relatively small number of unusually dense objects. The box could still look half empty while the load is already too heavy for one of the components in the system.
Conversely, lightweight and bulky belongings can occupy a large proportion of the available volume without weighing nearly as much.
A full roof box isn't necessarily overloaded, and an overloaded roof box isn't necessarily full.
What Happens If You Put Too Much Weight in a Roof Box?
Exceeding the specified limits can place inappropriate loads on the roof box, mounting system and vehicle roof. It can also adversely affect the way the vehicle behaves.
Additional weight carried high on a car changes its centre of gravity and can influence handling. Combined with the aerodynamic effect of the roof box itself, this is another reason to stay within the specified limits and drive appropriately for the vehicle's load and conditions.
If you're preparing for a longer journey, Can You Drive on the Motorway With a Roof Box? looks specifically at motorway driving, crosswinds, loading and journey checks.
Does the Weight Affect Fuel Economy?
Weight is one factor, although the aerodynamic drag created by carrying a roof box is also important.
The effect on fuel consumption or electric-vehicle range varies according to the car, box, load, speed, route, weather and driving style.
If you're budgeting for a long holiday journey, our Do Roof Boxes Reduce Fuel Economy? guide explains this in more detail.
What About SUVs and 4x4s?
Don't assume that a larger vehicle automatically means an unlimited or exceptionally high roof capacity.
An SUV or 4x4 still has manufacturer-specified limits, as do the bars and box fitted to it. These should be checked for the particular vehicle and setup.
The same applies to different manufacturers. Whether you're driving a Toyota, BMW, VW, Mercedes, Ford or Audi, vehicle-specific information matters more than a general assumption based on its size or badge.
Does a Heavier Roof Box Change the Height of the Car?
Weight and height are separate considerations.
Even a lightly loaded roof box still increases the physical height of the vehicle once it is installed. That's important when approaching garages, multi-storey car parks, hotel parking and other height-restricted entrances.
See How Much Height Does A Roof Box Add To A Car? for more on calculating and remembering your complete travelling height.
What If I'm Taking the Roof Box Abroad?
The same weight limits don't disappear when you leave the UK. If you're loading for a longer European holiday, it can actually become more important to resist the temptation to pack everything you might possibly need.
Check the vehicle and equipment specifications, pack deliberately and make sure you're also within the wider vehicle weight requirements applicable to your journey.
For overseas travel, see Can You Take A Roof Box To Europe?. If your journey starts with a sea crossing, Can You Take A Roof Box On A Ferry? covers ferry bookings, vehicle dimensions and luggage considerations.
Check Before You Load
Before filling your roof box, establish:
- The maximum permitted roof load for your particular vehicle.
- The relevant load limit for the roof bars and mounting equipment.
- The relevant load limit for the roof box.
- The weight of the box, bars and other equipment that counts towards the vehicle's roof load.
- How much capacity remains for suitable luggage once those factors are taken into account.
If you're uncertain about a specification, check the manufacturer's documentation rather than guessing.
Professionally Fitted Roof Box Hire in the Midlands
Midlands Roof Box Hire provides professionally fitted roof boxes for customers heading on family holidays, weekends away and longer road trips. Our customers travel to us from areas including Redditch, Burton-upon-Trent, Sutton Coldfield, Hinckley and Birmingham, with our main base in Tamworth.
Professional fitting is included with our roof box hire service, and compatible bars can be supplied where required. Read Does roof box hire include fitting? for more information about the process.
If you're still deciding which capacity you need, Which Is The Best Roof Box? and What Can You Put in a Roof Box? are useful next steps.
Weight Matters More Than Empty Space
The key thing to remember is that the amount of luggage that physically fits inside a roof box and the amount of weight you're permitted to carry are not the same thing.
Check the limits applying to your vehicle, bars and box, include the weight of the roof-mounted equipment where applicable, and never exceed the lowest relevant limit. Pack suitable luggage evenly and securely rather than simply continuing until the box looks full.
Browse our Roof Box Range, check how much it costs to hire a roof box or Contact Us with your registration and travel dates to discuss roof box hire for your next journey.