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The Outback has the longest roof of the three current Subaru models, and it’s the one most often loaded up for road trips and camping. That combination means Outback owners tend to size up faster than Forester or Crosstrek owners — a box that looks oversized on a shorter roof usually still leaves room to spare on an Outback.
Capacity isn’t the only variable, though. Here’s how to pick a size that actually fits your Outback and your hatch.
Quick Picks
- Best for most Outback owners: Thule Motion XT L — around 18 cubic feet, the practical default for road trips and camping gear.
- Best alternative brand: Yakima SkyBox 18 — same size class, worth comparing if you prefer Yakima’s mounting hardware.
- Best for families: Thule Motion XT XL — steps up capacity for families or gear-heavy trips.
- Best for extended trips: Thule Motion XT XXL — maximum capacity; verify hatch clearance before buying.
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Choosing a Cargo Box Size for an Outback
The Default: Around 18 Cubic Feet
For most Outback owners, an 18-cubic-foot box like the Thule Motion XT L covers the common case — road trips, camping gear, and family travel — without adding more roof bulk than necessary. The Yakima SkyBox 18 sits in the same class if you’d rather buy Yakima.
Sizing Up: Where the Long Roof Pays Off
This is the one upgrade where the Outback has a real edge over the other two Subaru models. Its longer roof gives an XL box more room to sit without crowding the windshield or overhanging the hatch as much as it would on a shorter vehicle. For families or anyone who regularly runs out of room, the Thule Motion XT XL is worth the extra size — and if you’re packing for extended trips, the Thule Motion XT XXL is about as large as it makes sense to go.
Hatch Clearance Is the Real Limit, Not Cubic Feet
Two boxes with similar capacity can have very different lengths, and length — not volume — is what causes hatch interference. The Outback’s long roof gives more room to work with than a Forester or Crosstrek, but a box mounted too far back can still catch the hatch on the way up. Adjusting crossbar spread and sliding the box forward usually solves it without needing a smaller box.
Outback vs Forester vs Crosstrek Cargo Box Sizing
| Model | Roof Length | Loading Height | Realistic Ceiling |
|---|---|---|---|
| Outback | Longest of the three | Moderate | XL boxes, with room to spare |
| Forester | Moderate | Tallest — more reach to load | Large; XL adds real loading effort |
| Crosstrek | Shortest, narrowest | Lowest, easiest to reach | Medium-Large; XL is a stretch |
The Outback is the one Subaru where sizing up rarely causes problems — the roof length absorbs it. On a Forester or Crosstrek, the same box demands more attention to positioning.
Cargo Box Size by Outback Generation
The 2010-2014 (fourth-gen) and 2015-2019 (fifth-gen) Outbacks both handle medium and large boxes comfortably, with XL sizes requiring closer attention to hatch clearance. Current-generation (2020-present) Outbacks offer the most flexibility of the three, including XL boxes with proper fitment. The Outback Wilderness shares the same roof dimensions as the standard Outback, but its taller ride height makes loading slightly more work — worth factoring in if you load solo.
Common Mistakes Outback Owners Make
- Buying XL “just in case.” A bigger box adds wind noise and weight year-round — size for what you actually carry, not the one trip a year that needs more.
- Ignoring box length in favor of cubic feet. Two boxes with the same capacity can have very different hatch clearance.
- Leaving the box mounted year-round. It adds drag and noise even empty — worth removing between trips.
FAQs
What size cargo box fits a Subaru Outback?
Most Outbacks comfortably run 15-20 cubic feet, and many can size up to 21+ with proper hatch clearance — the long roof gives more headroom than a Forester or Crosstrek.
Can an Outback fit a 21+ cubic foot box?
Yes — the Outback is the most forgiving of the three Subarus for XL boxes, though hatch clearance is still worth verifying before buying.
Does the Outback Wilderness fit the same box sizes?
Yes, the roof dimensions match the standard Outback. The taller ride height just makes loading a bit more work.
Does a larger box hurt gas mileage?
Yes. Larger boxes add aerodynamic drag and are most noticeable at highway speeds — one more reason to size for typical use, not the biggest trip of the year.
Final Thoughts
The Outback’s long roof makes it the easiest Subaru to size up for road trips and family travel — an 18-cubic-foot box covers most owners, and stepping up to XL rarely causes the hatch and clearance problems it would on a shorter vehicle. Match the size to what you actually carry, and double-check hatch clearance once it’s mounted.
Recap: Best Cargo Box Sizes for a Subaru Outback
- Thule Motion XT L — best for most owners
- Yakima SkyBox 18 — best alternative brand
- Thule Motion XT XL — best for families
- Thule Motion XT XXL — best for extended trips
Related Guides
• What Crossbar Length Do You Need?
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