Find a seat › Diono › Radian 3QX
Diono Radian 3QX fit guide
Steel-framed all-in-one that holds three-across in many mid-size back seats; folds flat for travel. Here's exactly which children it fits, how NHTSA rated it, and which cars it fits — including three-across.
Which children it fits
| Mode | Weight | Height | LATCH limit |
|---|---|---|---|
| Rear-facing | 4 lb – 50 lb | up to 44" | up to 40 lb on lower anchors |
| Forward-facing harness | 22 lb – 65 lb | up to 57" | up to 40 lb on lower anchors |
| Belt-positioning booster | 40 lb – 120 lb | up to 57" | up to 40 lb on lower anchors |
Weight/height limits are the seat's NHTSA-published values. Beyond the LATCH limit, install with the vehicle seat belt instead of the lower anchors. Always follow the labels on your seat and the vehicle manual.
NHTSA Ease-of-Use detail
NHTSA's Ease-of-Use rating measures how easy a seat is to install and use correctly — the single biggest factor in real-world safety, since most seats are installed wrong. It is not a crash-test score; NHTSA does not crash-rate individual car seats.
Which cars the Radian 3QX fits three across
At 17" wide, three Radian 3QXs should fit across the back of these vehicles we track (test-fit to confirm):
Will it fit your exact car?
Check the Radian 3QX against a specific vehicle — single position and three-across:
Common questions
What are the weight and height limits of the Diono Radian 3QX?
Rear-facing: 4 lb–50 lb and up to 44" tall; Forward-facing harness: 22 lb–65 lb and up to 57" tall; Belt-positioning booster: 40 lb–120 lb and up to 57" tall. These are the manufacturer's NHTSA-published limits — always defer to the label on your seat.
How is the Diono Radian 3QX rated by NHTSA?
NHTSA gave the Diono Radian 3QX an Ease-of-Use rating of 3/5 stars, including 4/5 for vehicle-installation features. Ease-of-Use measures how easy the seat is to install and use correctly — not crash performance, which NHTSA does not rate for individual seats.
Can the Diono Radian 3QX fit three across?
The Diono Radian 3QX is about 17" wide. Three should fit across the back seat of 60 of the vehicles we track, including the 2015–2024 Subaru Outback, 2020–2024 Toyota Highlander, 2016–2022 Honda Pilot.
Sources: ratings, modes & recalls — NHTSA (pulled 2026-06-18); external width — Diono published spec (steel-framed, 17 in). Informational only — built from NHTSA public car-seat ratings and published seat/vehicle dimensions. This is not a safety certification and not a substitute for the seat and vehicle manuals. Always confirm the fit and install yourself before every trip.