Best Roof Cargo Boxes (2026)
November 8, 2026 · 19 min read
You have four people, a week of luggage and a trunk that swallows two suitcases. That is the moment most people start looking at cargo boxes, and the moment they find that the number on the lid tells them almost nothing useful. Eighteen cubic feet sounds like plenty until you learn it holds six carry-ons, not nine, and that the tail hangs 27 inches behind your rear crossbar.
Updated — first published
Quick answer
For most families a 500-litre roof box is the right size: the Thule Motion 3 XL measures 202 x 74 x 37 cm inside, which takes six standard 22 x 14 x 9 inch carry-ons lying flat plus soft bags on top. Going up to 600 litres adds length and depth, not a seventh suitcase.
Thule Motion 3 XL
500 litres with a published internal measurement, so you can check your luggage against it before you buy.
SportRack Vista XL
Same 18 cubic feet, 21 inches shorter than the Thule, and you give up dual-side access and a serious lock.
Thule Motion 3 XXL
Buy it for 215 cm skis and long awkward gear, not for an extra suitcase, because there is not one.
Who this guide is for
This is for someone who already has crossbars on the roof, or is about to fit them, and wants extra car storage for two or three trips a year. Every box here is a hard shell that clamps to a pair of crossbars, so none work on a bare roof or on side rails alone.
This is for you if
- You have factory or aftermarket crossbars already on the car
- Four or more people travel with a week of luggage
- You carry skis, snowboards or camping gear that will not go in the trunk
Look elsewhere if
- Your car has no crossbars and you do not want to buy a rack first
- You park in a garage under 7 feet and cannot add any roof height
- You would rather hang the load off the back, in which case read our best hitch cargo carriers (2026)
How these picks were chosen
Every number in this guide comes from the maker’s own spec sheet or product page, and the picks were ranked on internal space and fit rather than on the cubic-foot figure printed on the lid. Where a maker does not publish a measurement, this guide says so instead of estimating it.
Our selection method
- Thule’s Motion 3 boxline spec sheet, Yakima’s SkyBox NX 18 page, SportRack’s Vista XL page and Inno’s Wedge 660 specification were compared in November 2026.
- Published internal dimensions were weighted most heavily, because they decide how many suitcases fit and nothing else does.
- Soft roof bags, hitch trays and baskets were excluded: they solve a different problem and carry different risks.
- Rear overhang figures in this guide are geometry, worked out from published exterior length and crossbar spread, not a measurement taken on a car.
- Specifications come from manufacturer documentation. Cedar Buy does not physically test products — see our editorial policy.
Quick comparison
The column that decides most purchases is exterior length, because that is what collides with your hatch and your garage, not the volume.
| Product | Volume | Exterior length | Best for | Link |
|---|---|---|---|---|
| Thule Motion 3 XLBest overall | 500 L (18 cu ft) | 84.6 in (215 cm) | Families of four or five | Amazon → |
| SportRack Vista XLBest value | 18 cu ft (510 L) | 63 in (160 cm) | Two trips a year, short roofs | Amazon → |
| Thule Motion 3 XXLPremium | 600 L (21 cu ft) | 91.3 in (232 cm) | Skis to 215 cm, long roofs | Amazon → |
| Inno Wedge 660 | 11 cu ft | 80 in (203 cm) | Low garages and sedans | Amazon → |
| Yakima SkyBox NX 18 | 18 cu ft (509 L) | 84 in (213 cm) | Skiers who want a fit chart | Amazon → |
What the table does not show
Two boxes can hold the same 18 cubic feet and swallow a different number of suitcases, because the shape of the space matters more than the size of it. A long shallow box and a short deep box both reach 510 litres and only one of them takes a hard-sided case lying flat.
Litres versus what actually fits
A standard US carry-on measures 22 x 14 x 9 inches, and the only way to know how many of them fit is to divide the box’s internal measurements by those three numbers. On that arithmetic the Thule Motion 3 XL takes six carry-ons lying flat, and so does the Motion 3 XXL despite holding another 100 litres.
The XXL’s interior is 220 x 77 x 40 cm, longer and deeper than the XL but not wide enough for a third case across. The extra volume is real and it goes to soft bags, mats and skis, not to another suitcase.
Internal height is the measurement that catches buyers out on low-profile boxes. The Inno Wedge 660 is 8.5 inches tall inside, which is half an inch shy of a 9-inch carry-on, so the lid will not close on one lying flat. If you mostly carry skis and boards, read our guide to the best ski and snowboard cargo boxes (2026) before you decide on a general-purpose box.
| Box | Volume | Internal L x W x H | Carry-ons lying flat | What the rest of the space takes |
|---|---|---|---|---|
| Thule Motion 3 XL | 500 L | 79.5 x 29.1 x 14.6 in | 6 | About 5 in of headroom above the cases for coats and duffels |
| Thule Motion 3 XXL | 600 L | 86.6 x 30.3 x 15.7 in | 6 | The extra 100 L is length and depth, not a seventh case |
| SportRack Vista XL | 18 cu ft | Not published | Not calculable | Exterior is 63 x 38 x 19 in, the widest and deepest shape here |
| Inno Wedge 660 | 11 cu ft | Internal height 8.5 in; length and width not published | None, the lid will not close on a 9 in case | Flat gear: skis, folding chairs, soft duffels |
| Yakima SkyBox NX 18 | 509 L | Not published | Not calculable | Exterior 84 x 36 x 16.5 in; takes skis and boards to 195 cm |
Length versus rear hatch clearance
What hits your tailgate is not the box’s length but the part hanging behind the rear crossbar, which on a long box mounted centrally is over two feet. Subtract your crossbar spread from the box length, then halve it.
Most crossbar pairs sit 24 to 40 inches apart, and 30 inches is a fair middle for a crossover. At that spread a 91-inch box leaves 30 inches of tail behind the rear bar and a 63-inch box leaves 16.5 inches.
| Box | Exterior length | Crossbar spread allowed | Rear overhang at 30 in, centered | Exterior height |
|---|---|---|---|---|
| SportRack Vista XL | 63 in | Not published | 16.5 in | 19 in |
| Inno Wedge 660 | 80 in | 23.5 to 39.25 in | 25 in | 11 in, and 9.6 in of that sits above the bars |
| Yakima SkyBox NX 18 | 84 in | 24 to 40 in | 27 in | 16.5 in |
| Thule Motion 3 XL | 84.6 in | Not published in the boxline sheet | 27.3 in | 16.9 in |
| Thule Motion 3 XXL | 91.3 in | Not published in the boxline sheet | 30.7 in | 17.7 in |
Sliding the box forward on the bars shifts overhang from the back to the front, which is why Thule markets the Motion 3’s forward position as giving trunk access. Yakima goes further and publishes a per-vehicle hatch clearance chart with the SkyBox NX 18, the only thing here that answers the question for your exact car.
Height bites in parking garages. The Inno Wedge 660 adds 9.6 inches above the crossbars against an 11-inch box height, because its hardware is recessed. Measure from the ground to the top of your crossbars, add that figure, and compare it to the clearance sign.
Aerodynamics and fuel cost
A roof box costs you fuel, and the US Department of Energy puts the penalty for a large, blunt box at 2 to 8 percent in city driving, 6 to 17 percent on the highway and 10 to 25 percent at 65 to 75 mph. The spread is that wide because the effect depends almost entirely on speed and on the car underneath.
Oak Ridge National Laboratory measured both ends of it: at 65 mph the same box cut a 2009 Toyota Corolla’s fuel economy by 25 percent and a 2009 Ford Explorer’s by 10 percent. A small car pays roughly double what a tall SUV pays.
So drive 65 rather than 75 on the long legs, and take the box off when the trip is over. If that number is what is stopping you, a hitch-mounted carrier costs only 1 to 2 percent by the same Department of Energy figures. Between modern boxes, frontal area decides it: the 11-inch Inno Wedge 660 is the cheapest here to run and also holds the least.
Security and locking
No plastic box is theft-proof, so what a lock really buys you is protection from the opportunist and a catch that cannot be left half-closed at 70 mph.
Thule’s SlideLock on the Motion 3 separates locking from opening and will not let the key come out unless the lid is latched, so a closed box is a locked box. Yakima’s SkyBox NX 18 uses full metal locking handles with SKS locks, which both secure the contents and clamp the box to the vehicle. The SportRack Vista XL has a single basic lock and a rear opening, which is the honest trade you make at that end of the market.
One-key systems matter if you already run racks or bike carriers from the same brand, which makes this a brand decision as much as a security one — see thule vs yakima: which brand for your roof.
Thule Motion 3 XL — Best overall
It earns the slot because Thule publishes the internal measurement, 202 x 74 x 37 cm, so you can check your own suitcases against it instead of guessing from a cubic-foot number.
Thule Motion 3 XL
Best for a family of four or five with a week of luggageThis is the 500-litre size in Thule’s Motion 3 boxline, 215 cm long and opening from either side of the car. It mounts with PowerClick, a clamp whose torque indicator clicks when it is tight enough. What sets it apart here is that Thule tells you what is inside it.
Price and availability change often — check the current listing.
Check price on Amazon → Paid link.Strengths
- Published internal dimensions, so capacity is checkable
- Opens from both sides, useful on a curbside load
- SlideLock keeps the key captive until the lid is latched
Limitations
- At 215 cm it needs a long roof and leaves about 27 in behind a 30-inch crossbar spread
- Takes 5 to 7 pairs of skis but only to 200 cm, so 215 cm skis need the XXL
Editorial opinion
Buy it if your crossover or wagon has roof enough for 215 cm and you want one box for luggage and ski gear. Skip it on a compact sedan, where the fuel penalty is steepest.
If you want to know the capacity before the box arrives, this is the one.
See it on Amazon →SportRack Vista XL — Best value
It earns the slot on shape rather than price: 18 cubic feet packed into 63 inches, which is 21 inches shorter than the Thule and the easiest box here to place on a small roof.
SportRack Vista XL
Best for two or three trips a year on a shorter roofThe Vista XL is a UV-resistant ABS shell measuring 63 x 38 x 19 inches, short and deep where the others are long and shallow. It opens at the rear only, and the mounting hardware needs no tools.
Price and availability change often — check the current listing.
Check price on Amazon → Paid link.Strengths
- Shortest box here at 63 in, about 16.5 in of overhang on a 30-inch spread
- 38 inches wide and 19 deep, a forgiving shape for bulky soft bags
- Tool-free mounting, lock included
Limitations
- Rear opening only, so you load it standing behind the car
- SportRack does not publish internal dimensions or a ski length
Editorial opinion
Buy it if the box lives in the garage 50 weeks a year and your roof is too short for an 84-inch shell. Skip it if you load on a busy street or need to carry skis.
If your roof is short and the box comes off after every trip, this is the one.
See it on Amazon →Thule Motion 3 XXL — Best large
It earns the slot for length, not for suitcase count: 220 cm of internal floor and skis up to 215 cm, which nothing else here will take.
Thule Motion 3 XXL
Best for long gear on a full-size SUV or minivanThe 600-litre size in the same boxline, 232 cm long with a 220 cm internal floor, and the same PowerClick mount, SlideLock catch and 75 kg limit as the XL. What you are buying is reach: the extra 100 litres is length and depth, not another suitcase slot.
Price and availability change often — check the current listing.
Check price on Amazon → Paid link.Strengths
- Takes skis to 215 cm, the longest of the five
- 220 cm internal floor swallows camp chairs, poles and mats whole
- Same mount and lock as the XL
Limitations
- At 232 cm it leaves about 30 in behind a 30-inch crossbar spread, enough to meet a tailgate
- Holds the same six carry-ons as the XL, so the extra volume only pays off on odd shapes
Editorial opinion
Buy it if you ski on 200 cm-plus gear or run a full-size SUV with roof to spare. Skip it if you are buying size for its own sake, because the extra 100 litres only helps with soft and awkward loads.
If your gear is long rather than merely plentiful, this is the one.
See it on Amazon →Inno Wedge 660 — Best low-profile
It earns the slot on one published number: 9.6 inches of added height above the crossbars, which is what gets you into a parking garage.
Inno Wedge 660
Best for sedans, low garages and flat gearAn 11 cubic foot box measuring 80 x 33 x 11 inches, lower than anything else here, opening from both sides and fitting spreads from 23.5 to 39.25 inches. The catch is interior height: 8.5 inches rules out hard-sided cases lying flat.
Price and availability change often — check the current listing.
Check price on Amazon → Paid link.Strengths
- Adds only 9.6 in above the bars, the lowest here by a wide margin
- Smallest frontal area of the five, so the smallest fuel and noise penalty
- Dual-side opening despite the slim shell
Limitations
- 8.5 in inside means no hard-sided carry-on lies flat
- 11 cubic feet is a third less than the 18 cubic foot boxes here
Editorial opinion
Buy it if your garage or your sedan rules out a tall box and you pack soft. Skip it for a family’s hard luggage, because 8.5 inches of headroom is not something you can work around.
If clearance decides the purchase, this is the one.
See it on Amazon →Yakima SkyBox NX 18 — Also worth a look
It earns a place for one reason the others do not offer: Yakima publishes a hatch clearance chart by vehicle, so you can check your own car before ordering.
Yakima SkyBox NX 18
Best for skiers who want to confirm fit firstEighteen cubic feet in an 84 x 36 x 16.5 inch shell, opening from both sides, taking skis and boards to 195 cm on spreads from 24 to 40 inches. Full metal locking handles secure the contents and hold the box to the car at once.
Price and availability change often — check the current listing.
Check price on Amazon → Paid link.Strengths
- Per-vehicle hatch clearance chart, unique in this group
- Metal locking handles rather than plastic latches
- 24 to 40 inch spread suits most factory racks
Limitations
- At 53 lb it is the heaviest here and a genuine two-person lift
- Yakima does not publish internal dimensions for the NX line
Editorial opinion
Buy it if you want hatch clearance confirmed for your exact vehicle first, or already run Yakima racks. Skip it if you lift the box alone, because 53 pounds overhead is the practical limit.
If you want the fit answered for your car before you order, this is the one.
See it on Amazon →What to look for before you buy
Internal length matters more than anything else, because it decides whether your longest item goes in at all. Work down from there to crossbar spread, opening side and, last of all, the volume printed on the lid.
Internal length and height
Measure your longest bag and your tallest one against the published interior. For family luggage you want at least 14 inches of interior height; under 10 inches and you are packing duffels only.
Crossbar spread
Crossbars are the two bars running across your roof, and the gap between them is the spread. Most boxes want 24 to 40 inches, and outside that range the clamps simply will not reach.
Which side it opens
Dual-side opening lets you load from the curb rather than the traffic lane. A rear-opening box is fine if you always load in a driveway, and it is usually the cheaper shell.
The cubic-foot number on the lid
Ignore it when comparing two boxes. The Thule Motion 3 XL and the Yakima SkyBox NX 18 are both 18 cubic feet and different shapes, so they hold different things.
Key terms, explained
Three phrases do most of the damage here, because makers use them loosely and buyers read them literally.
Plain-language definitions
- Crossbar spread
- The distance between the centers of the two bars running across your roof, typically 24 to 40 inches on a car. A box states a minimum and maximum spread it can clamp to, and outside that range it simply will not mount.
- Height above the crossbars
- How much taller your car becomes once the box is on, which is less than the box’s own height because the mounting hardware is recessed into the base. The Inno Wedge 660 is 11 inches tall and adds 9.6 inches.
- Dual-side opening
- A lid hinged so it can be unlatched and lifted from either side of the car. Buyers often assume it means the box opens front and rear as well, and it does not.
Mistakes that cost people money
The expensive mistake is buying on volume and discovering the box does not clear your hatch, because a mounted box is awkward to return and a 90-inch carton is worse.
- Buying on cubic feet instead of internal dimensionsTwo 18 cubic foot boxes hold different luggage. Treat an unpublished interior as a warning to pack soft.
- Never measuring the crossbar spreadMeasure center to center and compare with the box’s stated range. It is the one thing that can make a box unmountable.
- Forgetting the garageAdd the box’s above-crossbar height to your crossbars, not to the roofline. The difference is several inches.
- Leaving the box on all yearAt 65 to 75 mph a large box costs 10 to 25 percent of your fuel economy, and an empty box costs the same as a full one. Taking it off after the trip is the cheapest thing in this article.
Frequently asked questions
How many suitcases fit in a roof cargo box?
A 500-litre box takes about six standard 22 x 14 x 9 inch carry-ons lying flat, based on the Thule Motion 3 XL’s published interior of 202 x 74 x 37 cm. Going to 600 litres does not add a seventh, because the extra space is length and depth rather than another row across. Soft bags fill the remaining headroom.
Will a roof box stop my tailgate opening?
It depends on how far the box hangs behind your rear crossbar. Subtract your crossbar spread from the box length and halve it: an 84-inch box centered on a 30-inch spread leaves about 27 inches of tail. Sliding the box forward reduces that, and Yakima publishes a per-vehicle clearance chart for the SkyBox NX 18.
How much fuel does a roof cargo box use?
The US Department of Energy puts a large, blunt box at 2 to 8 percent in city driving, 6 to 17 percent on the highway and 10 to 25 percent at 65 to 75 mph. Oak Ridge National Laboratory measured a 25 percent drop on a compact sedan at 65 mph and 10 percent on an SUV with the same box, so small cars pay roughly double.
Do I need crossbars to fit a cargo box?
Yes. Every hard-shell box here clamps to a pair of crossbars running across the roof, and none mount to a bare roof or to the raised side rails alone. If your car has side rails but no crossbars, you need to buy crossbars first, matched to your vehicle.
So which one should you buy?
Buy the Thule Motion 3 XL unless your roof is too short for 215 cm, in which case buy the SportRack Vista XL.
| If you need | Best pick | Key spec | Buy |
|---|---|---|---|
| Best overall | Thule Motion 3 XLBest overall | 202 x 74 x 37 cm inside, six carry-ons flat | Amazon → |
| Best value | SportRack Vista XLBest value | 63 in long, the shortest shell here | Amazon → |
| Best large | Thule Motion 3 XXLPremium pick | Skis to 215 cm on a 220 cm floor | Amazon → |
| Best low-profile | Inno Wedge 660 | 9.6 in above the crossbars | Amazon → |
| If you are still unsure | Thule Motion 3 XL | The only 500 L box here with a published interior | Amazon → |
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