radian® 3RX

2020 edition

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the original 3-across car seat

what's new about the 2020 model?

Rear-facing For Longer

Now up to 50 lbs / 22.7 kg

Head Support

New head support infant insert for cushioned comfort

Improved Fabrics

New and updated fabrics that are easy to remove and wash

Instruction Booklet

New booklet to improve the user experience

car seat installation

why parents love me

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I use the Radian 3RX and we are so grateful that it is so narrow, as we have to fit 3 carseats in our vehicle! The material is soft and comfortable and because it is made of steel, it really puts me at ease and reminds me that they are safe in their diono car seat.


product specs

product specs

5-50 lbs / 2.3-22.7 kg

22-65 lbs / 10-29.5 kg

Booster mode
40-120 lbs / 18-54 kg

Seated torso height
7.5-16.5" / 19-42 cm

Overall maximum height
up to 57" / 144.8 cm

care & maintenance

Cover machine washable at 86F/30C/Cold


tips and tricks

installation tips

    • read the manual the comes with your car seat
    • read the vehicle manual
    • find a certified child passenger safety instructor or technician to help you and check your installations
  • airline use

    • unfold the Diono car seat before boarding the plane and ask the flight attendant for seatbelt extenders
    • make sure to install the car seat next to the window so passengers can get by in case of an emergency
    • make sure to take the slack out of the seatbelt extender before connecting to the airplane seatbelt
  • rear-facing installation

    • first secure the detachable base and slide in the locking mechanism
    • adjust the harness to be the proper height for rear facing
    • adjust the head support to fit your child properly
  • folding & unfolding

    • to unfold: lay the car seat down on a stable flat surface and undo the velcro strap, tuck it in behind the fabric and open seat until clicked and locked.
    • to fold: remove the red velcro strap from behind the fabric and loosen up the harness as much as possible so they are at the top of the car seat. release the lever at the bottom of the car seat and push seat inward - secure the top with the red velcro strap.
  • right for newborn?

    • whether you buy an infant only car seat or an all-in-one convertible car seat, both car seats have to meet the same standard
    • seats like the Diono all-in-one convertible car seats come with an infant cushion insert to properly fit your child in the harness
    • all-in-one convertibles are more economical - they have a lot of room for growth for your growing child
  • baby on board!

    Keep the little ones comfortable and positioned well when on the move, and stay one step ahead with cleverly designed accessories.

    why parents chose me

    The Original 3 Across

    Features a slimline, space saving design at only 17" wide, that allows you to install three across in most vehicles

    Head Support Infant Insert 

    The removable head support infant insert features paddes support for cocooned comfort. Easy to remove as your infant grows.

    Rear-Facing for Longer

    With extended rear-facing from birth up to 50 lbs / 22.7 kg to keep your child in the safest position for as long as possible.

    Easy Remove Covers

    When the next journey gets messy, easily remove the cover to machine wash and dry.

    award winning car seats

    three's not a crowd.

    buy now

    parents' choice

    your choice

    colours that speak all languages

    parents love the radian® 3RX!

    "My family and I were traveling on vacation, and had an accident after being hit by a semi. Our vehicle did several spins, and rolled several times. My one year old son was seated behind the passenger's seat, the side of impact. As we were rolling his window broke. Once we came to a complete stop, his seat had not moved. He had NO injuries. He was the only one in the car completely unharmed. The car was totalled. I'm convinced it's because of the reinforced steel/aluminum frame. I'm forever grateful for how well made this carseat is. Thank God for the friends who purchased it as a shower gift. This carsest saved my baby's life."

    -Grateful Mom, Cincinnati, OH

    "I have now had the Diono RXT in Spring print with the angle adjuster for about 6 weeks now. I love this seat I love its low profile sides its 45lbs weight limit and that it can be used with an AA to give it a more upright angle and more front to back space. I found it east to install and adjust. I maybe alone on this but I love the shoulder pads. I would most defiantly recommend this to my friends looking for a seat to last a good couple years. My only cons with the seat is it is quit heavy at 25lbs and its only really good for rf and ff as the booster function is often out grown when the the harness is out grown ff. Other then that a great choice."

    -Mom22, Silverdale, WA

    We bought this car seat about 5 months ago and it was the best decision! We searched and searched for the perfect car seat that was 1st of all safe, user friendly, long lasting, and stylish. My mom had purchased a different convertible seat for her vehicle for my daughter, but once she saw mine, she returned hers and purchased the same exact one I have. The red is beautiful ❤️ Thank you Diono for giving us the confidence my little girl is safe.

    -Pitss Family, Post Falls, ID

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    can the radian 3RX fit 3-across in my car?

    Most likely, yes, as long as you have 51" (129.6 cm) in the back row from vehicle armrest to armrest. It may be necessary to install all three using the vehicle seat belt system..

    can the harness straps be cleaned?

    Yes, we recommend using a damp cloth with a solution of water and baking soda to wipe the straps clean. They cannot be saturated in any liquid, or they will need to be replaced. Replacement harness straps can be purchased on our website.

    can I use the radian 3RX from birth?

    Yes, the weight limits on all our convertible car seats starts at 5lbs. The newborn must also meet a length requirement where the top of their shoulders reaches the lowest harness slot on the seat.

    are the harness pads and buckle pads required on my seat?

    Yes, they are required while your child is sitting in forward-facing. They are optional but recommended while sitting in rear-facing. The center buckle pad is required at all times.

    can the memory foam be washed?

    Yes, it can be hand washed in cold water and air dried.

    what are the requirements to use the seat in booster mode?

    The child must weight at least 50lbs and be at least 40 inches tall.