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Diono Radian 3QX Ultimate 3 Across All-in-One Convertible Car Seat

$ 369.99 USD

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The ultimate 3 across All-in-One car seat from birth to booster (4 - 120 lb / 1.8 - 54 kg).

Featuring 3 stages of complete rear-facing protection and all new Diono Safe+TM engineering to provide the next generation in car seat safety.

What’s new for 3QX?

  • Suitable from 4 lb / 1.8 kg
  • Extended rear facing up to 50 lb / 22.7 kg
  • Easy remove covers - machine wash and dry
  • Improved rear-facing recline
  • Comfort+ memory foam cushion for improved seat base comfort
  • Safe+TM easy adjust 12 position headrest with 22% increase in occupancy space from the R series
  • Safe+TM steel core
  • Safe+TM headrest with built in side impact protection
  • Safe+TM side impact protection with extended sidewalls
  • Safe+TM steel anti-rebound bar
  • Safe+TM 2-in-1 infant positioning liner
  • Safe+TM anti-slip harness pads
  • Safe+TM newborn travel high wedge for optimum newborn positioning
  • Safe+TM roll-over tested
  • Safe+TM side impact tested
  • Improved headrest design made with high performance foam padding for child comfort
  • Premium soft fabrics and detailing
  • Latch and rear facing tether storage
  • Instruction manual storage
  • Improved seat base design with expandable seat width
  • Easy-access side storage for harness cleaning/replacement

What makes it great

Features Safe+TM newborn travel high wedge, Safe+TM 2-in-1 infant positioning liner and Safe+TM steel anti-rebound bar to provide new levels of rear-facing protection to the original 3 across.

  • Creates near lie-flat travel position for newborns while reducing head slump and keeping airways open. Simply remove as baby grows.
  • Gives extra infant comfort and toddler body support. Simply remove as baby grows.
  • SAFE+TM STEEL ANTI-REBOUND BAR Reduces rebound rotation by 50%. One click connection to the seat base and fits against vehicle seat back. Prevents the seat from rebounding or “bouncing back” into the vehicle seat in the event of a collision.

Radian® 3QX is subjected to a combination of the most rigorous side impact and rollover testing to make sure we have the safest seat possible.

With 4 ways to travel from birth to booster, the Radian® 3QX adapts as your child grows to offer a custom fit from birth to 120 lb.

Designed and engineered with all new Diono Safe+TM protection. Now you can keep your child rear facing for even longer up to 50 lb (approx. 4 years old).

Built with our famous radian slim fit design, to fit 3 across in most vehicles without compromising child or passenger comfort.

Built with 6 layers of EPS & EPP foam, high density plastic and steel reinforcement to make ultimate side impact protection, without compromising 3 across slim fit design in most midsize vehicles.

All new upgraded mechanically engineered, reinforced steel core. Made from automotive grade high strength steel to shield and protect. Manages and dissipates energy.

Contoured and engineered with the latest European side impact research and technology in crash energy management. Features 22% increase in headrest range from the Radian R series with built in side impact protection to improve child head containment in the event of a collision.

The only all-in-one car seat that folds for easy travel and transport, FAA approved for use on aircraft.

Seat Weight

25.8 lb / 11.7 kg

Overall seat dimensions (lowest position inches)

H 28" x W 17" x D 16"

Overall seat dimensions (lowest position cm)

H 71cm x W 44cm x D 41cm

Overall seat dimensions (highest position inches)

H 31" x W 17" x 16"

Overall seat dimensions (highest position inches)

H 80cm x W 44cm x D 41cm

Vehicle seat bite to front FF length

17” / 44cm

Inside shoulder width

12” / 31cm

Inside hip width

12” / 31cm

Inside seat depth

13” / 33cm

Rear facing installation depth

30”/ 76.2cm

Inside seat height
(base to accommodating)

26” / 67cm

External widest point (without Safe+ Side Impact Management Pod)

17” / 44cm

Rear Facing (RF) convertible weight limit

4 – 50 lb / 1.8 – 22.7 kg

Forward Facing (FF) convertible weight limit

22 – 65 lb / 10 – 29.5 kg

Belt Positioning Booster (BPB) Mode weight limit

40 – 120 lb / 18 – 54 kg

Belt Positioning Booster (BPB) Mode height limit

57" / 145 cm

We are happy to accept returns on unused, unaltered merchandise in its original packaging and with all original tags. Return requests must be made within 7 days from the original date of purchase for a refund (less any shipping fees) and within 30 days for store credit or exchange. All returns must be pre-authorized by a Tadpole staff member, either in person, or by phone or email if you are mailing the merchandise back. Damaged packaging will be subject to a 10% restocking fee. All unaltered merchandise could also be subject to a restocking fee anywhere between 10-25% depending on the value of the original merchandise and the reason for return. Once we have received your return we will process the refund/store credit/exchange within 2 business days. Store credit expires after 6 months. 

The following items are final sale i.e. NON-REFUNDABLE:

  • All special orders and sale items; all furniture sales are final sale; damaged, defective, or missing furniture pieces will be replaced.
  • All stroller and car seats sales are final; damaged merchandise will be covered under the manufacturer's warranty.
  • All opened breastfeeding products, opened feeding products, body products are final sale.
  • All pantry items are final sale. 
  • Gift cards are non-refundable. 
  • Gifts can only be exchanged or offered store credit if returned within 30 days of the original date of purchase. 

Please note:

Orders that qualify for free shipping may be subject to a restocking fee.

If an item is damaged once opened, or during shipping, please notify us immediately. We will gladly accept returns of defective merchandise within 7 days of purchase/receipt of goods. Returned items are your responsibility until they reach the return address. Please ensure your package is returned securely to prevent any damage to the item or its packaging. Tracking is highly recommended. Any returns that are damaged when we receive them will not be refunded. We are not responsible for any items that are returned to us in error. 

Credit card orders will receive refunds in the form of a credit to the card. Please allow at least one billing cycle for credit to appear on your statement.

To request a return via email, send an e-mail to with your name, address, invoice number, item you are returning, and why you are returning it. 

Important: Please note that we do not refund delivery fees or original shipping charges.

Please send returns to:
Attn: Returns
58 Clarendon Street
Boston, MA 02116