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Roof Cargo Box Sizing and Choosing Guide


Article Categories: Other | Travel

If you like to take lots of gear with you on camping trips or to participate in your favorite outside activities, you may want to consider buying a roof cargo box. Roof cargo boxes are one of the easiest ways to carry lots of gear with you safely and securely.

There are many things to consider before choosing a roof cargo box, including the sizing. Here is a complete guide to choosing and buying a roof cargo box.


What Is A Roof Cargo Box?

A roof cargo box is a cargo storage solution that mounts to the top of your car. Made of tough, rugged plastic, these boxes connect to your crossbars with hardware meant to withstand the elements. They are durable, weather-resistant, and keep your cargo locked and secure as you travel.

Roof cargo boxes can be found in many sizes, including extended lengths for large cargo like cross-country skis. They mount on any vehicle type and can often be used in conjunction with other rack accessories.


Roof Cargo Box Requirements

To use a roof cargo box on your vehicle, you will need to have crossbars installed. Make sure that the cargo box you choose will work with your particular crossbar model, especially if they’re factory-installed. Some companies like Thule make their cargo boxes to fit their crossbars, so they might not work with all pre-installed crossbars. When purchasing a cargo box, they should have a chart or tool to check compatability.

The roof of your vehicle must be able to support the weight of the cargo box, crossbars, crossbar supports, and the items packed inside. We will discuss this in more detail later on, and it means that you should know the maximum amount of weight you can put on your vehicle’s roof before you choose a cargo box (though most items stored in cargo boxes will not hit that overall limit for most vehicles).

Finally, you must choose a cargo box that doesn’t interfere with your vision or your vehicle’s operating capabilities. You must be able to close your rear hatch and be able to see out of the front and back of your vehicle.


What Fits In A Roof Cargo Box?

The interior dimensions of your roof cargo box determine what all you can put in it. Usually the dimensions are expressed in cubic feet or liters, but sometimes manufacturers will list the actual dimensions of the box. This is very useful when determining whether or not long pieces of gear, like cross country skis, will fit in your cargo box.

Most people don’t have a specific number of liters or cubic feet in mind when they look for a rooftop cargo box.  To get a general idea of how much gear capacity you need based on the number of people you have with you, check out the chart below.


Number of People Gear Capacity
2 12 cubic feet/340 liters
3 15 cubic feet/425
4 18 cubic feet/510 liters
5 21 cubic feet/595 liters
6 22+ cubic feet/623+ liters


This is a general guideline for camping, hiking, and general outdoors pursuits; alpine activities like skiing and snowboarding may vary based on the size of your equipment. These values are approximate, and the amount of space you need varies based on the equipment you bring and how you pack it. For example, most alpine skis are between 150 cm and 190 cm (59-75 inches), so you need to make sure your box is long enough if you plan on transporting skis in your cargo box.


Popular Rooftop Cargo Boxes

The below list is just meant to highlight some common sizes and brands. Some of these are long enough for skis of all sizes, like the Yakima Skybox 12, while others are shorter and more suited to carrying other gear like the Thule Pulse.

Model Weight Exterior


Interior Dimension Maximum Cargo Weight Link to Product
Thule Pulse Rooftop Cargo Box, Medium 34 pounds 67 x 35 x 16 inches 61 x 33 x 14 inches; capacity is 14 cubic feet (396 liters) 110 pounds REI
Yakima SkyBox 18 52 pounds 94 x 38 x 18 inches Dimensions not listed; capacity is 18 cubic feet (510 liters) 165 pounds Amazon
JEGS Rooftop Cargo Carrier 35 pounds 61.25 x 39 x 12 inches Dimensions not given; capacity is 18 cubic feet (510 liters) 110 pounds See on Amazon
Inno Wedge 660 42 pounds 80 x 33 x 11 inches Dimensions not listed; capacity is 11 cubic feet (311 liters) 42 pounds Amazon
Yakima SkyBox 12 41 pounds 92 x 24 x 16 in (One of the narrowest boxes on the market) Dimensions not listed; capacity is 12 cubic feet (340 liters) 165 pounds Amazon
Thule Force Rooftop Cargo Box, 22 52 pounds 90.5 x 35.5 x 18.5 in Dimensions not listed; capacity is 22 cubic feet (623 liters) 165 pounds REI


How To Choose A Roof Cargo Box

The first thing you should do when considering which cargo box to buy is to think about what cargo you’ll be carrying with you. Cargo boxes are great for all kinds of gear. They’re great for holding your camping gear, like tents, sleeping bags, camp furniture, and more. They’re popular with skiers and can safely hold skis, poles, ski boots, and snowboards.

The best use of your rooftop cargo box is for lightweight yet bulky objects– tents, duffel bags, boots, bags, reel boxes, rod cases, and other similar equipment can all go in a roof cargo box.

It’s best to keep heavy items in the car. Most cargo boxes are designed to hold up to 150-165 pounds. Any more than that will damage the roof of your car– and even if your roof box is designed to carry 165 pounds, you can’t necessarily put 165 pounds in it. You can’t overload the roof capacity of your car– but more on that later.


How Much Can I Fit On My Roof?

Rooftop cargo boxes don’t always take up the full capacity of your roof, and you can often get other gear up there. The following chart gives you an estimate of what you can fit on your roof with a cargo box.

Crossbar Length Gear
50 inches 1 cargo box, 1 bike
51-60 inches 1 cargo box, 2 bikes
60+ inches 1 cargo box, 1 kayak or 2+ bikes


If you want to stow other gear on your roof, make sure that you don’t overload it. If you want to put a cargo box and a bike on the roof, you can’t safely fill the cargo box to its maximum capacity.

On our car, we have a small Thule box for camping gear, and on the other side of the roof, we actually can have a fly rod roof rack that we occasionally swap out of a small ski rack.


Know Your Car’s Roof Carry Limit

To figure out how much you can safely put in your roof cargo choice, look up the recommended maximum load for your vehicle. This will be in the owner’s manual, and is also easily found online. Then, subtract the weight of the cargo box and other rack accessories like bike racks or fly rod rod racks. If you’re using aftermarket crossbars or hardware, subtract that weight as well. The remaining amount of weight is the maximum for how much you can safely pack in your roof cargo box.

We will note that most vehicles have a weight limit maximum that is much higher than what you should be placing on your roof during motion (dynamic load limit). The weight limit at standstill is different from the moving limit. Many smaller vehicles are around 150 pounds, which means one cargo box with ski gear isn’t going to get to that amount, but heavier gear can get there pretty quickly.

Car Rooftop Weight Limits


Gas Mileage

Your gas mileage will change significantly with a roof cargo box. Even the most streamlined roof cargo box is going to impact your vehicle’s mileage, and this becomes more distinct the shorter your vehicle is. In one Consumer Reports test, adding a roof rack and rooftop cargo box dropped a sedan’s gas mileage by 19%. However, for an SUV, the fuel economy only dropped by 13%. It is worth noting that these tests were done at highway speeds, which will have a much greater effect on mileage than around town driving with roof racks.

With rising fuel costs, this is something you should consider strongly when choosing a cargo option for your vehicle. There are ways to improve the fuel economy, like choosing a streamlined option and using the smallest option possible for your cargo needs.

Another consideration is the ability to remove the rack when not in use. Easy to remove racks can help you save on fuel economy if you take advantage of that feature.

Rooftop cargo carriers of any kind have more of an impact on your vehicle’s mileage than hitched cargo carriers on the back of the vehicle. While those do impact the economy a little bit due to their weight, they don’t disrupt air flow as much and cause less drag. However, rooftop cargo boxes can hold more and may be easier to pack.


The Different Dimensions of Cargo Boxes

Look at the height, length, and width of your cargo box. Two cargo boxes with the same interior volume might have different dimensions, thereby being able to fit different types of gear.



Most cargo boxes are at least 6 feet long; some are longer. A 6-foot (72 inch) box will fit skis up to 180 cm long, or about 5 feet 10 inches. If you never plan on carrying lengthy items, a shorter box will work well for you– but if you like cross-country skiing or fishing with long rods, you might want a longer box.

The length and overall size of your vehicle may have an impact on your choice of box length. Larger vehicles, like SUVs, full-size pickups, and larger station wagons, can have boxes of any length. But smaller, more compact boxes like hatchbacks and sedans work better with shorter boxes.



Wider roof boxes have more storage capacity than narrower boxes. But narrower boxes mean that you can have other rack accessories, like bike racks, kayak racks, fly rod roof racks, or ski racks. If you want to carry gear on the roof alongside your cargo box, a narrow box is a better choice. The wider your box, the greater wind resistance, and therefore the worse your fuel economy will be.



Generally, you want the shortest roof box you can find. While taller boxes have an increased capacity, taller boxes also prevent you from driving from certain places and increase the wind resistance of your vehicle. The taller the box, the worse your fuel economy will be.


Hatch Clearance

Hatch clearance is extremely important, especially if you have a hatchback or SUV with a rear door. If your cargo box doesn’t have full hatch clearance, you won’t be able to use this door. This is one reason it’s a good idea to look at cargo boxes in person, because you’ll be able to check the hatch clearance yourself.

If you’re buying a roof cargo box online, here’s how to check the hatch clearance:

  • Move the front crossbar as far forward as you can, if you can move it.
  • Measure from the center of the front crossbar to the open back hatch at the level of your crossbars.
  • Compare that measurement to hatch clearance on the cargo box manufacturer website.
  • If your measurement is larger than the clearance number listed for a cargo box, the cargo box will fit.


Bigger Isn’t Always Better

Some people are tempted to buy the biggest roof cargo box they can afford. But this is actually a bad idea. You want to buy the smallest cargo box that will work for you. Bigger cargo boxes:

  • Are more expensive
  • Are heavier
  • Cause a bigger drop in fuel economy
  • Are cumbersome
  • Produce more road noise
  • Are harder to unpack


Streamlined Boxes

Some roof cargo boxes have a streamlined design. These boxes don’t have as much of an impact on your fuel economy as standard cargo boxes. They have a lower capacity, and you have to carefully pack them because there’s less space at the front. But if you are only packing for two or three people, a streamlined roof cargo box is a good option.


Cargo Box Appearance

For many people, this is a minor consideration. Cargo boxes only come in a few colors, usually black and silver. Sometimes you can get white or red, but there just aren’t many options.

Cargo boxes can come in shiny or matte finishes. If you have a choice, choose what you prefer– though if you like to put park stickers or race stickers on your cargo box, shiny boxes hold stickers better than a matte texture. Matte finishes won’t show dirt and dust as much as shiny finishes.


How To Use A Roof Cargo Box

Once you’ve chosen a roof cargo box, you will need to install it on your vehicle. This is done by either tightening clamps or using bolts to attach your cargo box to the roof rack. Once you’ve made sure that the cargo box is securely attached and doesn’t shift or wobble when the vehicle is in motion. Orient the box as straight as possible. If the front and back aren’t perfectly aligned, you’ll be adding wind resistence.


Packing a Roof Cargo Box

When you pack your roof cargo box, pack most of the weight in the middle of the box. At least 60% of the weight should be evenly distributed between the crossbars of the roof rack. The remaining weight should be evenly distributed between the front and the back. Don’t pack too much weight in either end of the cargo box.

Don’t put your immediate needs in your roof cargo box– objects can shift during travel, so it’s best not to open the cargo box until you get to your final destination and you can safely unpack.


Closing and Locking Your Roof Cargo Box

This might sound silly, but plenty of people forget that they have a cargo box on top of their vehicle. We’ve watched boxes open and spew gear on the highway. Closing your cargo box isn’t enough– you have to lock it before you take off down the highway. Otherwise you may face an unpleasant surprise when you take a sharp turn or drive into the wind, and your gear may end up scattered all over the road.

The easiest way to avoid this? Keep your cargo box key on the same keychain as your car key. By design, the keys for cargo box locks usually can’t be removed from the lock when the box is unlocked. So if your car key and the cargo box key are on the same keyring, it’s impossible to remove the key and start driving before you close and lock the box.


Driving With a Roof Cargo Box

You must know the height of your vehicle with the cargo box before you start driving with it. It is easy to accidentally collide with low-clearance structures, like the top of your garage door, drive-throughs, and parking garage entrances. Use a tape measure to figure it out, and keep the number handy so that you don’t forget.

Some people like to put a note on their garage door, or a traffic cone so that they stop and remember that there’s a rooftop cargo box. Driving into a space too short for the cargo box is a great way to damage your cargo box, the top of your car, and whatever you drove into.


Storing Your Roof Cargo Box

When you aren’t using your roof cargo box, you should detach it from your vehicle. This will save fuel economy and wear and tear on the box. Store your cargo box in a cool, dry place, and don’t store it on its side or end. Make sure that it isn’t in direct sunlight, which can damage the plastic over time.

If you want to store it on its base, you can prop it up with boards or cinderblocks to keep the mounting hardware off the floor. You can also get suspension kits for roof cargo boxes so that you can hang them from the roof of your garage or shed.

Max DesMarais

Max DesMarais

Max DesMarais is the founder of hikingandfishing.com. He has a passion for the outdoors and making outdoor education and adventure more accessible. Max is a published author for various outdoor adventure, travel, and marketing websites. He is an experienced hiker, backpacker, fly fisherman, backcountry skier, trail runner, and spends his free time in the outdoors. These adventures allow him to test gear, learn new skills, and experience new places so that he can educate others. Max grew up hiking all around New Hampshire and New England. He became obsessed with the New Hampshire mountains, and the NH 48, where he guided hikes and trail runs in the White Mountains. Since moving out west, Max has continued climbed all of the Colorado 14ers, is always testing gear, learning skills, gaining experience, and building his endurance for outdoor sports. You can read more about his experience here: hikingandfishing/about