Cargo Carrier Sizes: Roof Boxes, Roof Bags and Hitch Carriers
Extra cargo space goes either on the roof or on the hitch. The right size depends less on how much you want to carry than on what your roof or hitch is rated for. Here are the standard sizes and the limits that decide between them.
Roof cargo boxes range from about 10 to 22 cu ft (280-620 L) and 55-92 in (140-235 cm) long; a 16 cu ft (450 L) box about 77 in (195 cm) long suits most crossovers. Hitch cargo baskets are typically 48 or 60 in long and 20-24 in deep (122-152 × 51-61 cm), rated around 500 lb (227 kg) on a 2 in receiver. Either way, the carrier and cargo together must stay within the roof or tongue-weight limit.
- Roof box volume
- 10-22 cu ft (280-620 L)
- Roof box length
- 55-92 in (140-235 cm)
- Hitch basket
- 48-60 × 20-24 in
- Basket rating
- about 500 lb (2 in)
On this page
Types of cargo carriers compared
| Type | Typical size | Load range | Mounts on |
|---|---|---|---|
| Roof cargo box | 10-22 cu ft (280-620 L) | 100-165 lb (45-75 kg), limited by the roof | Crossbars |
| Roof cargo bag | 10-21 cu ft (280-595 L) | Limited by the roof | Crossbars, side rails, or straps through the door frames |
| Roof basket | about 40-60 × 35-40 in platform | Limited by the roof | Crossbars |
| Hitch cargo basket | 48-60 × 20-24 in (122-152 × 51-61 cm) | 300-500 lb, limited by the hitch | 1 1/4 or 2 in receiver |
| Hitch cargo box | about 13-22 cu ft enclosed | Limited by the hitch | 2 in receiver, usually |
The roof and the hitch have very different limits. A typical crossover roof is rated for about 150 lb while driving, but its Class III hitch may accept 500 lb or more of tongue weight. That is why heavy items belong on the hitch.
Roof cargo box sizes
Boxes are sold by volume, but length decides whether the box fits your roof and carries skis, and width decides whether a bike fits next to it.
| Size | Volume | Outside length | Best for |
|---|---|---|---|
| Small | 10-13 cu ft (280-370 L) | 55-65 in (140-165 cm) | Compact cars, hatchbacks |
| Medium | 14-16 cu ft (400-450 L) | 65-77 in (165-195 cm) | Compact and midsize crossovers |
| Large | 17-18 cu ft (480-510 L) | 77-85 in (195-215 cm) | Midsize SUVs, wagons; skis to about 200 cm |
| Extra large | 20-22 cu ft (570-620 L) | 85-92 in (215-235 cm) | Full-size SUVs, minivans; long skis |
For example, Thule's Motion XT line spans 400 L (M, about 175 cm long), 450 L (L, 195 cm), 500 L (XL, 215 cm) and 610 L (XXL, 232 cm). Most boxes are 30-36 in (76-91 cm) wide and 14-18 in (36-46 cm) tall. Narrow "sport" boxes of about 25 in (63 cm) wide leave room on the bars for a bike or kayak.
Choosing a roof box length
- Measure the roof from the top of the windshield frame to the rear edge of the roof.
- Open the rear hatch and measure how far forward of the roof's rear edge the top of the open hatch reaches. The box must stop short of that point, or the hatch will hit it.
- Keep the front behind the windshield top, or at most a few inches over it, so it does not catch wind or block the view through the sunroof.
- Check the mounting range: the box's clamps must line up with your crossbar spread. See the roof rack size guide for bar lengths and spacing.
A 16 cu ft (450 L) box takes roughly four duffel bags or two large suitcases plus soft bags. Sloped front and rear ends lose space, so packing soft luggage works better than rigid cases. For bag dimensions, see the luggage size guide.
Roof cargo bags
Soft bags come in about the same volumes as boxes, 10-21 cu ft (280-595 L), and fold flat for storage. They can strap to a bare roof through the door frames, but a non-slip mat underneath is needed to protect the paint. Bags are water-resistant rather than waterproof at the zips, and they flap at highway speed unless filled tight. Weight limits still come from the vehicle's roof rating.
Hitch cargo carrier sizes
| Platform size | Metric | Typical rating | Receiver |
|---|---|---|---|
| 48 × 20 in | 122 × 51 cm | 300-500 lb | 1 1/4 or 2 in |
| 60 × 20 in | 152 × 51 cm | 500 lb | 2 in |
| 60 × 24 in | 152 × 61 cm | 500 lb | 2 in |
Side rails are usually 4-6 in (10-15 cm) high. The basket itself weighs about 30-60 lb (14-27 kg), and that weight counts against the tongue weight limit. Hitch cargo boxes (enclosed, lockable) are usually about 48-60 in long and 13-22 cu ft.
Hitch classes and tongue weight
| Class | Receiver size | Max tongue weight | Max trailer weight |
|---|---|---|---|
| Class I | 1 1/4 in | 200 lb (91 kg) | 2,000 lb |
| Class II | 1 1/4 in | 350 lb (159 kg) | 3,500 lb |
| Class III | 2 in | 500-800 lb (227-363 kg) | 5,000-8,000 lb |
| Class IV | 2 in | 1,000 lb (454 kg) | 10,000 lb |
| Class V | 2 or 2 1/2 in | above 1,000 lb | above 10,000 lb |
Work out the cargo allowance as the lowest of the hitch rating, the vehicle's tongue weight limit and the carrier's rating, minus the carrier's weight. A 50 lb basket on a Class II hitch (350 lb) leaves 300 lb for cargo. The same basket on a Class III hitch is usually limited by its own 500 lb rating: 450 lb of cargo.
A hitch extender moves the load farther behind the axle, increasing leverage on the hitch. Hitch makers commonly rate tongue weight at half or less with an extender. Avoid them for heavy loads.
Clearance, length and legal checks for hitch carriers
- Vehicle length: a hitch basket adds about 24-30 in (61-76 cm) behind the bumper, which matters in garages and parking spaces. See the car dimensions guide for garage sizes.
- Ground clearance: the platform sits near bumper height. Steep driveways and ramps can scrape it; rise-style shanks lift it 2-4 in, but also add leverage.
- Lights and license plate: most US states require the rear plate and lights to stay visible. A loaded basket can block both, so many owners fit a plate holder and light kit to the carrier.
- Rear access: fixed carriers block the tailgate; tilt-away or swing-away designs let it open.
Pickup alternatives
Pickups have extra options: bed racks and tonneau-top boxes, bed extenders that add 1.5-2 ft of length with the tailgate down, and hitch carriers for when the bed is full. Bed sizes by truck are in the truck bed size guide. For long gear such as skis, the ski size chart helps match box length to ski length, and campers can pair a large box with the tents in the camping tent size guide.
Frequently asked questions
What size roof box do I need?
For a compact car or small crossover, 11-14 cu ft (310-400 L); for midsize SUVs and wagons, 14-18 cu ft (400-510 L); for full-size SUVs and minivans, up to 22 cu ft (620 L). Check that the box's rear edge clears the open hatch and that its front stays behind the windshield top.
Will skis fit in a roof box?
Skis fit if they are shorter than the box's inside length, which is about 10-15 cm less than the outside length. A 215 cm (85 in) box takes skis up to about 200 cm; a 175 cm box suits skis up to about 160 cm. Ski lengths by height are in the ski size chart.
How much weight can a hitch cargo carrier hold?
The lowest of three figures: the carrier's rating (often 500 lb on 2 in carriers), the hitch's tongue weight rating (200 lb for Class I, 350 lb for Class II, 500-1,000 lb for Class III-IV), and the vehicle's tongue weight limit in the owner's manual. Subtract the carrier's own weight from the limit to get the cargo allowance.
Is a roof box or a hitch carrier better?
A hitch carrier takes more weight, loads at waist height and costs less fuel. A roof box keeps rear access and the backup camera clear, is enclosed and lockable, and suits long items such as skis. Light, bulky gear suits the roof; heavy gear suits the hitch.
Do cargo carriers reduce gas mileage?
According to the US Department of Energy, a large roof-top cargo box can cut fuel economy by 2-8% in the city, 6-17% on the highway and 10-25% at 65-75 mph, while rear-mounted cargo boxes and trays cost only about 1-2% in the city and 1-5% on the highway.