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Driving Through Washington State? Know The Booster Seat Laws (2024)

The state of Washington legally requires children under 4’9” tall to be secured in a booster seat or car seat.

Children under the age of 4 must be secured in a rear-facing or forward-facing car seat with separate harness.

But children age 4 and over may be secured in a booster seat once they outgrow their forward-facing car seats.

Booster Seat Requirements Washington

child in booster seat puts on seat belt

Children must be at least 4 years old to transition to a booster seat in Washington.

Once a child transitions to a booster seat, the child must be secured in a booster seat until they reach ONE of the following requirements:

  • Booster Seat Age Washington: unspecified
  • Booster Seat Weight Limit: unspecified
  • Booster Seat Height Limit: 4’9”

There is no minimum age for transitioning from a booster seat to a seatbelt in Washington state.

All children must be secured in booster seats until they are tall enough to properly fit a seatbelt – 4’9”.

Booster seats must be secured in the backseats of vehicles when available.

Booster Seat Backseat Exceptions

All booster seats must be secured in the backseats of vehicles in Washington when available.

A backseat is not available when:

  • The vehicle does not have a backseat.
  • The seatbelts in the backseat are broken or there is another issue with the vehicle that makes restraint in the rear seat dangerous.
  • You are transporting multiple children of car seat/booster seat age, and all backseat seatbelts are in use with other car seats or booster seats.

Where can I get my booster seat checked or installed in Washington?

Many fire stations, police departments, and medical centers in Washington have certified Child Seat Safety Technicians on staff who can help you install a car seat (or check your installation) by appointment.

The University of Washington maintains a small running list of Car Seat Check locations by county.

You can also contact Safe Kids Washington, led by the Washington State Department of Health, if you need help finding a certified technician in your area.

General Booster Seat Laws FAQ

Are booster seats effective?

Yes. Very.

According to the CDC, “booster seat use reduces the risk for serious injury by 45% for children age 4-8, when compared with seat belt use alone.”

When can a child use a booster seat?

A child can use a booster seat when she outgrows her forward-facing car seat with a harness.

Though the laws on front-facing car seats and booster seats differ by state, for safety’s sake your child should stay in a front-facing (harnessed) child seat until he reaches the maximum height or weight on the seat.

When can a kid stop using a booster seat?

The minimum safe height for use of a regular seat belt without a booster seat is 4’9”.

Due to this, it is recommended your child ride in a booster seat until they are at least 4’9” tall, regardless of their age.

Not all state laws support this.

Many states have minimum ages at which children may transition to regular seatbelts, no matter how tall they are.

But if you want your child to be the safest they can be on the road, you should keep them in a booster seat until they reach 4’9”.

What is the booster seat weight limit?

Different booster seats have different weight limits, typically 100-120 pounds.

But weight isn’t the main determiner of when a child should move from a booster seat to a seat belt.

Height is more important to a seat belt’s fit.

That said, your child should never ride in a booster seat once they exceed the weight limit.

The seats are designed to be safe only for those under the maximum weight.

So, if your child has outgrown the weight limit on their booster, upgrade them to a booster with a higher weight limit or make the transition to a regular seatbelt.

What’s the best booster seat?

The best booster seat is the one that will do the most effective job of keeping your child safe in the event of an accident.

According to Consumer Reports, the top-performing booster seats on the market (as of July 2022) are:



Buy at:

Graco Turbobooster Grow

Graco Turbobooster Grow

Buy at:

Peg Perego Viaggio Shuttle Plus 120

Peg Perego Viaggio Shuttle Plus 120

Buy at:

But you don’t have to buy a separate booster seat if you have a convertible car seat.

For convertible toddler-booster seats and all-in-one car seats with booster functionality, see our car seat buying guide Which Car Seat To Buy: Making Sure Your Little Ones Stay Safe On The Road.

When were booster seats invented?

The very first child seats for cars were more booster seats than car seats.

They were literally designed to “boost” children up so they could see better (and so parents could see them), but they had no built-in safety features.

Booster seats as we know them today, with their focus on transitional safety between car seats and seatbelts, have only been around since the late-1990s to early 2000s when laws requiring them started being implemented.

When did booster seats become mandatory?

Booster seats are not mandatory in all states.

Some states have younger minimum ages and no height requirements for transitioning children from child seats to seatbelts.

In those states, children can typically move directly from forward-facing car seats to regular seatbelts.

As for the states that do have mandatory booster laws, the first laws (Tennessee and South Carolina) went into effect in 2001.

Bridging the Gap Between Car Seats and Seatbelts

Car seats are designed to protect the smallest of children, while seatbelts are only safe for children over a certain height (4’9”).

Booster seats bridge the gap between the two.

Washington’s requirement that children be secured in a booster seat until 4’9″ tall coincides with the safe height for seatbelt use.

So, follow Washington law and keep children in a booster until they reach 4’9″.

And, before that, follow the state’s car seat laws.

For more on Washington’s car seat laws, see Washington State Car Seat Laws.

And for more on child passenger safety in Washington, see Washington State Front Seat Law.

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