Diono Monterey 4DXT vs Cosco Topside

Both are booster car seats — here are their published manufacturer specs side by side.

This compares published manufacturer specs — not safety or fit advice. The seat's manual, your vehicle's manual, NHTSA's tools and a certified CPST are the fit-and-safety authority; always check them before installing.

Spec	Diono Monterey 4DXT	Cosco Topside
Stage	Booster	Booster
Narrow (3-across)	✓	–
Extended rear-facing	–	–
FAA-approved	–	–
Lightweight / travel	–	✓

How they differ

• the Diono Monterey 4DXT is listed narrow (roughly ≤17″) for fitting three across a back seat; the Cosco Topside isn't listed narrow
• the Cosco Topside is the lighter, more travel-friendly model

Where to buy

Check the Diono Monterey 4DXT price on Amazon →

Check the Cosco Topside price on Amazon →

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FAQ

What's the difference between the Diono Monterey 4DXT and the Cosco Topside?
The Diono Monterey 4DXT is narrow for 3-across; the Cosco Topside is lightweight/travel. Both are booster car seats.

Which fits three across, the Diono Monterey 4DXT or the Cosco Topside?
The Diono Monterey 4DXT is listed narrow (~≤17″) for 3-across; the Cosco Topside isn't. Three-across fit still depends on your exact vehicle — confirm before buying.

Which is right for my car and child, the Diono Monterey 4DXT or the Cosco Topside?
That depends on your specific vehicle and child — this page compares published manufacturer specs only, not fit or safety. Check the seat manual, your vehicle manual, NHTSA's car-seat finder and ideally a certified CPST before deciding.

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