Diono Radian 3RXT vs Britax Allegiance

Both are convertible 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.

As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. Weight ranges are the manufacturer's published limits across all modes.

How they differ

• the Diono Radian 3RXT is listed narrow (roughly ≤17″) for fitting three across a back seat; the Britax Allegiance isn't listed narrow
• the Diono Radian 3RXT lists extended rear-facing (a higher rear-facing weight limit, ~40-50 lb); the Britax Allegiance doesn't

Published limits

Diono Radian 3RXT: All-in-one (rear-facing → forward-facing harness → high-back booster; no backless mode found in manual). Forward-facing also requires at least 1 year old + 22 lb minimum (printed manual requirement). No separate age requirement printed for booster mode. Expired over 10 years from date of PURCHASE (manual's own wording — most other brands print "manufacture").

Britax Allegiance: Harnessed seat only (no booster mode). Rear-facing 5–40 lb, forward-facing 20–65 lb; the manual's overall height limit is 49″ or less. Discontinue use once the seat is older than seven years (see the Manufactured Date Label).

Printed verbatim in the manufacturer's manual (Diono Radian 3RXT Car Seat Instruction Manual · Britax Emblem/Allegiance User Guide P11182000); “—” = not published for that mode, “not yet sourced” = we haven't read that manual yet, not that the seat has no limit. How we source these →

Recall record

Diono — 2 on NHTSA's record · Britax — 22 on NHTSA's record.

That is the record of the brand — not a verdict on these models. A recall names specific models and manufacture-date ranges, and a seat missing from the record is not "recall-free": check nhtsa.gov/recalls with the model and date of manufacture on your seat's label. Source: NHTSA, retrieved 2026-09-05.

Where to buy

Diono Radian 3RXT

See price on Amazon

Britax Allegiance

See price on Amazon

As an Amazon Associate we earn from qualifying purchases, at no extra cost to you. Affiliate links never affect our specs or which seats we compare.

FAQ

What's the difference between the Diono Radian 3RXT and the Britax Allegiance?
The Diono Radian 3RXT is narrow for 3-across, extended rear-facing, FAA-approved for aircraft; the Britax Allegiance is FAA-approved for aircraft. Both are convertible car seats.

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

Which is right for my car and child, the Diono Radian 3RXT or the Britax Allegiance?
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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