Roof Box Size Guide 2023

It sounds obvious, but when you are in the process of choosing a roof box you need to make sure that as well as giving you the extra space you want, your chosen box also fits on your car.  

It can be very easy to focus on either the cubic feet of the roof box or how wide and tall it is, but you have to take all of these factors into consideration.

Using a cargo box size guide is a great way to make sure that you understand the various sizes and factors that you need to consider when looking for a roof box.

Our roof box size guide groups our favourite boxes into size to make sure that you understand the various sizes and factors that you need to consider when looking for a roof box.

Roof Box Size Guide

Make sure that you pay attention to the length and width of the roof box, because an extra inch or so of height really doesn’t make a lot of difference to how much you are going to be able to store in the roof cargo box. 

Additionally, by taking into consideration the external dimensions of the roof box you want to buy, you can make sure that it won’t take up too much room on your roof rack or make accessing your hatch or seeing out of the front windshield difficult.

Here’s our Roof Box Size guide:

Choosing a Half-Width Roof Cargo Box

Average specification of a half width cargo box:

Roof boxes that are narrower are great if you want to be able to carry additional items on the roof rack as well as your box. 

This cargo box from Thule is only 25 inches wide, making it one of the skinnier models on the market today. While this does mean that you don’t have as much room inside to store your items, the roof box can be attached to the side of your roof rack instead of right in the middle. 

This allows you to securely attach other items to the roof rack as well, so that you can easily take more of your stuff with you. If you have a very large family or need many items protected from extreme weather during travel, then this roof box may not be large enough for you. 

It comes with great features, such as sturdy U-bolts that allow the box to mount securely to the roof rack and two locks to ensure that the box is closed tight. However, if you are in the market for a smaller roof box that won’t take up a lot of room on your vehicle or when it is in storage in the garage, then this is one that you might want to consider.

Choosing a Wide Roof Cargo Box

Average specification of a wide width roof box:

At 39 inches wide this is a much bigger box so you won’t be able to attach a lot of other additional items to the roof rack.

If you are worried about keeping your belongings safe and protected while you are on the road, this larger roof rack offers tons of internal space so that you can easily pack as much as necessary. 

With an 18 cubic feet capacity, this roof box is perfect for a family who loves to travel, but needs to bring a lot of supplies with them when they are on the road. Installing and storing a larger roof box is something that you need to take into consideration, and reading this roof box size guide will help you to make the right choice for your family. 

While this roof box is much larger than a half-width roof box, it can be assembled quickly and doesn’t require any tools. Additionally, it only weighs 28 pounds, which means that most people can easily lift and attach the roof box to their vehicle by themselves without much trouble.

Choose a Short Roof Cargo Box

Average specification of a short width cargo box:

Depending on the size and style of your car, you will need to take into consideration the length of your new roof box to ensure that it will not affect your line of sight or cause you to drive dangerously or erratically. 

Shorter cars can still have roof boxes, but it’s important that the box is sized correctly so that it doesn’t interrupt driving.

A roof box that is too long for your vehicle can make it difficult to open the hatch, if you have a hatchback, and can also impede your vision when you are on the road.

This cargo box from Pep Boys is much shorter than others on the market, but it still offers plenty of room inside for your things. At only 62.8 inches long, this smaller roof box will fit easily on a shorter car without being a nuisance. 

Of course, when you opt for a shorter roof box, you need to understand that they will often be much taller to compensate and provide the internal space that you want. This can affect aerodynamics, so it’s a good idea to consider all dimensions when you are specifically looking for a shorter roof box.

Choose a Long Roof Cargo Box

Average specification of a long roof box:

Longer vehicles can easily accommodate longer roof boxes without there being a problem, which provides you with a lot more options when you are in the market for a new roof box.

The great thing about longer roof boxes is that they will provide more internal space for you to be able to pack things like skis, snowboards, and even fishing poles without them being damaged. If you want to bring certain sports gear with you, make sure that the roof box you choose offers enough internal space for the items you want to pack.

Not only can this roof box accommodate skis and snowboards up to 72 inches long, but it is very sleek and aerodynamic, so you don’t have to worry about a major decrease in your gas mileage when using this roof box. 

This roof box is made from 80% recycled material and features internal lid stiffeners. This is an important feature in a longer roof box, as they will ensure that your lid doesn’t bend or become warped when you are opening and closing it.

Choose a Small Capacity Roof Cargo Box

Average specification of a small capacity roof box:

You might only want enough extra room for a few smaller essential items, so there’s no reason to look at the larger roof boxes out there. Smaller roof boxes are generally less expensive, lighter, easier to store, and very easy to attach and remove from your car. 

With an internal capacity of nine cubic feet, this roof box isn’t large enough to store long items, but is ideal for storing extra clothing, toys, or gear that won’t fit in the car.

In general, a small roof box such as this option from JEGS is going to be ideal for a smaller family. At only 21 pounds, you can easily and quickly lift this roof box up to the top of your car for installation, and then easily remove it again once you get back from your trip. 

When choosing a very small roof box such as this one, it is important that you make sure that it will fit the roof rack on your car. Check not only the internal space to make sure that it will meet your needs, but also the external dimensions so you won’t have problems with it fitting on your vehicle.

Choose a Large Capacity Roof Cargo Box

Average specification of a large capacity roof box:

This XX-Large, 22 cubic feet cargo box is sure to provide you with all of the space that you need when you are looking for storage for a road trip.

Not only is this roof box generous in size, but it has been designed to be as aerodynamic as possible so that your gas mileage isn’t negatively affected.

Because it is a larger roof cargo box, it has been designed with certain safety features in mind to ensure that you don’t run into problems when using the box. There are separate opening and locking functions on the slidelock system, so you never have to worry about whether or not the lid is securely closed and locked into place.

Very large roof boxes such as this one can often interrupt hatch movement, but this box is specifically designed to fit in a forward position on the roof to prevent this from occurring. You do need to make sure that its forward position won’t interrupt your driving so you can be safe on the road.


Hopefully we’ve made choosing the right roof cargo box for you and your family easier than ever thanks to this roof box size guide. Understanding the relationship between the internal capacity, width, and length of your new roof box will ensure that you are better equipped to choose the right cargo box for your car. 

Size Matters
While style and appearance are important, it’s the size that counts – carefully consider the size of the roof box you are thinking about buying so that you a) are positive that you will get enough space and b) it’s not actually too large for your vehicle. 

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  1. add to article take into account roof aerials and aerodynamic any roofbox follows existing line of windscreen i.e. dont overhang

  2. I need a long narrow box as I also carry a kayak sometimes. Can anyone out there CFC explain the difference between the Thule Alpine 500 and the Evolution 500 as they pretty much look the same!

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