Choosing the right cargo bag shouldn’t feel like guesswork. But let’s be honest: “Will this actually fit my roof rack?” is one of the most common questions we get — right up there with “Is 20 cubic feet actually big enough?” and “How do I measure this thing without getting on a ladder?”
Whether you’re loading up between crossbars, on a rooftop basket, or with a hitch-mounted carrier, this guide will walk you through exactly how to measure, match, and select the perfect cargo bag size for your setup.
Let’s make sure your next trip is packed perfectly, with no surprises at checkout or on the highway.
Step 1: Measure the Usable Space
For Crossbars Only
You're measuring the flat, supported area between the bars.
Measure:
• Length: Center of front crossbar to center of rear crossbar
• Width: Distance between the inner edges of your crossbars
• Height Clearance: Optional, but helpful for tall items or low garage doors
You’ll want a roof bag that fits comfortably within this footprint. Slight overhang is fine, but flopping edges? Less than ideal.
For Roof Rack Baskets
Baskets make things easier. Measure the inside dimensions of the basket:
Measure:
• Interior Length
• Interior Width
• Interior Height (rail height)
Then select a bag that fits inside these rails or one designed to pair with your basket. Bags that match your basket’s footprint create a tighter, more aerodynamic load.
For Hitch Carriers
Measure the usable platform area, not including any rounded corners or folding hinges.
Measure:
• Length (side to side)
• Width (front to back)
• Wall Height (if high-rail)
The bag should sit within the rail boundaries and not hang over the sides (which causes drag, wear, and unsafe load shift).
Step 2: Match Cubic Feet to Real-World Packing Needs
Cargo bags come in popular capacities:
• 15-16 cu ft — Weekend trips, small cars
• 20-25 cu ft — Road trips, SUVs, family packing
• 30-35 cu ft — Big gear haulers
• 40-50 cu ft — Oversized hitch carriers and heavy-duty packing
Remember:
Cubic feet measure volume, not shape.
Two 30 cubic feet bags may fit very differently depending on their footprint.
Step 3: Compare the Bag’s Footprint to Your Rack or Carrier
Cargo bag listings will give two types of measurements:
✔ The cubic footage
✔ The flat dimensions (L × W × H)
Always compare the flat dimensions first.
This determines whether the bag fits your rack platform or basket.
A perfect match has:
• Bag length ≤ rack length
• Bag width ≤ rack width
• Bag height appropriate for your needs (taller isn’t always better due to wind drag)
Step 4: Choose the Right Bag Style for Your Setup
For roof racks without baskets
Use bags with:
• Heavy-duty straps and hooks
• Strong tie-down loops
• Waterproof zipper flaps
• Anti-slip mats
These prevent shifting and protect your roof.
For roof rack baskets
Use bags shaped to sit inside the rails for the most secure fit.
These bags maximize space and stay aerodynamic.
For hitch carriers
Choose a bag designed specifically for hitch racks:
• Rectangular footprint
• Strong circle loops
• Vertical sidewalls
• Heavy-duty straps that cinch under the carrier frame
For larger platforms like 70"×30" or 72"×36", use high-capacity hitch bags (40–50 cu ft).
Step 5: Leave Room for Straps, Rail Height & Overhang
A good rule of thumb:
Leave at least 1–2 inches of space between the bag and the rack boundary for straps, compression, and easy loading.
If your basket platform has tall side rails (6"-14"), choose a bag that sits inside them rather than puffing over the top.
Step 6: Consider Your Packing Style
Think about how you typically pack:
• Lots of soft bags? → A tall, flexible bag works great.
• Rigid coolers, boxes, totes? → Look for a wide-design bag.
• Mix of everything? → Pick a mid-height bag that balances stackability and flexibility.
Quick Size Cheat Sheet
If you’re unsure, here’s a fast rule:
- Small SUVs / crossovers: 15–30 cu ft
- Full-size SUVs / minivans: 35–50 cu ft
- Hitch carriers (60" length): 20–35 cu ft
- Large hitch platforms (66"-72" length): 40–50 cu ft
Final Tip: The Bag Should Fit the Rack — Not the Car
Even if your vehicle is massive, the rack dimensions determine the correct cargo bag size.
When in doubt:
Start with the rack measurements → match the bag footprint → confirm the capacity → pack with confidence.
Ready to Size Up and Gear Up?
Whether you're packing for a cross-country move, a full-family vacation, or one extremely ambitious Costco haul, choosing the right cargo bag size makes all the difference. With the right measurements and the right setup, your trip gets easier, quieter, and a whole lot roomier.
At Mockins, we design our rooftop bags and hitch bags to be tough, weatherproof, and ridiculously easy to use — because adventure should be fun, not frustrating.
So grab that tape measure, pick the perfect fit, and get ready to roll out with more space than you ever thought your vehicle had.
Shop our full lineup of rooftop carrier and hitch cargo bags and find your perfect match today — your next adventure (and your backseat passengers) will thank you.
