My 9-year-old is 4'6". Booster or seat belt?
Booster. Washington's booster stage ends at 4'9", not at age 8 or 9. The child is still under the height line.
State law page
Washington Booster Seat Law (2026)
Washington uses stages: rear-facing until 2, forward-facing harness until 4, a booster until the child is 4'9" tall, and the back seat until 13.
Quick answer
Washington booster seat law: booster until 4'9", harness until 4, rear-facing until 2, back seat until 13
RCW 46.61.687, in force since January 1, 2020, is written in stages. A child under 2 rides rear-facing until reaching the seat's weight or height limit. A child under 4 rides in a forward-facing seat with a harness until reaching its limit. A child under 4 feet 9 inches rides in a booster seat, or uses a properly adjusted seat belt once the child reaches 4'9". A child under 13 rides in the back seat when practical.
Washington is one of the few states whose legal minimum matches national safety guidance almost exactly. That means there is little gap here between "what the law requires" and "what is safest."
If your child still needs a booster, a backless model such as the Graco TurboBooster 2.0 Backless Booster Car Seat is the simplest way to meet the rule once they have vehicle head support (a lower-cost backless option works too); younger children often do better in a high-back booster. Not sure which? Use the seat finder, or run the 5-step belt fit test before dropping the booster. Shopping links — see our affiliate disclosure.
Front seat rule: Children under 13 must ride in the back seat where practical (RCW 46.61.687). See front seat age by state for all 50 states.
Quick check
Which seat stage fits your child right now?
Enter age and height to see the usual next stage and the guide to read. This is a navigation aid, not a substitute for the Washington rule above or the seat label.
Snapshot
Washington booster seat law at a glance
Read this top to bottom. Each stage runs until the child reaches the current seat's height or weight limit, not just a birthday.
| Question | Washington answer |
|---|---|
| Under 2 | Rear-facing child restraint until the seat's weight or height limit |
| Under 4 | Forward-facing child restraint with a harness until the seat's weight or height limit |
| Under 4'9" | Child booster seat, or a properly adjusted seat belt once the child reaches 4'9" |
| Under 13 | Back seat when practical |
| Lap-only belt | Booster requirement does not apply in a seating position with only a lap belt |
| Fine | Traffic infraction; WTSC lists $136; dismissible on proof of acquiring a restraint within 7 days |
| Source checked | 2026-09-12; Revised Code of Washington 46.61.687 and Washington Traffic Safety Commission guidance were checked. |
2026 check
Washington booster seat law 2026 update
Washington is upgraded to an official-source page because its 2020 law is written the way safety guidance is written, in stages tied to the seat's limits rather than a single birthday.
For 2026 checks, the direct answer is: rear-facing until 2, forward-facing harness until 4, booster until 4'9", back seat until 13, and every stage runs until the child reaches the seat's height or weight limit.
The booster rule does not apply in a seating position that only has a lap belt, which matters for older vehicles and some third rows.
Stages
How Washington's stage-based rule works
Each stage has two conditions joined together: a minimum age (or, for the booster stage, a height), and the child having outgrown the previous seat's limits. A 2-year-old who still fits rear-facing stays rear-facing. A 4-year-old who still fits the forward-facing harness stays in it. The statute pushes children to the next stage only when the current seat is outgrown.
The booster stage is the one most parents ask about. It ends at 4 feet 9 inches, not at a birthday. A 9-year-old who is 4'6" is still in the booster stage under Washington law.
Back seat
Washington's under-13 back seat rule
The driver of a vehicle transporting a child under 13 must transport the child in the back seat positions where it is practical to do so. This sits alongside the restraint stages: a 7-year-old in a booster is expected in the back.
"Where practical" covers vehicles without a back seat and situations where every back seat position is already occupied by another child. It is not a general parental discretion clause.
Lap-only belt
The lap-belt exception for boosters
The booster requirement does not apply in a seating position where only a lap belt is available. A belt-positioning booster needs a shoulder belt to work. If your vehicle's only free position has a lap belt, the safer choice is a harnessed seat rated for lap-belt installation, or rearranging seating so the booster-age child gets a lap-and-shoulder position.
Fines
Washington booster seat fine and source verification
A violation of RCW 46.61.687 is a traffic infraction. The Washington Traffic Safety Commission listed the child restraint infraction at $136 in May 2024; the exact amount is set by the state court penalty schedule (IRLJ 6.2) and adjusted periodically. A first notice can be dismissed if the driver shows proof of acquiring an approved restraint within seven days.
RCW 46.61.687 includes a dismissal provision: a driver's first notice of infraction can be dismissed if the driver presents proof of acquiring an approved child restraint or booster within seven days, and has no prior violation. The statute is built to get seats into cars rather than collect fines.
The dollar amount comes from the state court penalty schedule, not the statute, and is adjusted periodically. Use the WTSC figure as current guidance and expect court costs on top.
Adult claims
Does Washington have an adult booster seat law?
No. RCW 46.61.687 covers children under 13 and children under 4'9"; it has no adult provision. A viral notice claiming Washington requires adults under a certain height to use booster seats is not this law; see the adult booster seat law fact check. Searches using the phrase "adult booster seat" usually mean the point when a child can move from a booster to the adult seat belt.
Parent scenarios
Washington booster seat questions parents usually mean
My 3-year-old is at the harness limit. Booster?
The forward-facing harness stage runs until age 4 and until the seat's limit. If the seat is truly outgrown before 4, the answer is a higher-capacity harnessed seat, not a booster.
Does my 12-year-old have to sit in the back?
Yes, where practical. The under-13 back seat rule applies regardless of restraint type.
Third row with only a lap belt?
The booster requirement does not apply in that position. That is a legal carve-out, not a recommendation; a lap-and-shoulder position with the booster is the safer setup.
Shopping picks
Booster seats parents commonly use at this stage
Shopping links, separate from the law and safety guidance on this page; they do not change what the state requires. See our affiliate disclosure.
Budget backless booster
Cosco Topside Backless Booster Car Seat — no-frills, rated 40 to 100 lb. Common for a second car or carpool duty.
Backless booster
Graco TurboBooster 2.0 Backless Booster Car Seat — the best-selling backless option, with cup holders, for a child who has vehicle head support.
High-back booster
Graco TurboBooster 2.0 Highback Booster Car Seat — for a child who still needs head and side support, or a vehicle seat with a low head restraint.
High-back to backless, 2-stage
Britax Skyline 2-Stage Belt-Positioning Booster Car Seat — converts from high-back to backless as the child approaches the thresholds on this page.
Not sure which type fits your child? Use the seat finder — enter age, height, and weight to see the stage and a matching seat.
Official sources
Washington law and safety links
State safety source: Washington Traffic Safety Commission enforcement notice (May 2024, lists the $136 fine)
Requirement and penalty statute: RCW 46.61.687
National safety guidance: NHTSA car seats and booster seats, CDC child passenger safety prevention, and AAP car safety seats guidance.
Legal note
This page is a plain-English guide, not legal advice. Recheck Revised Code of Washington 46.61.687 and state agency materials before relying on a requirement or a fine amount after a law change.
Next guides
Use these pages after checking Washington booster seat law
Booster Seat Requirements
Compare age, height, weight, and state-law requirements across the U.S.
Read requirementsBooster Seat Age
Use the age and stage timeline before moving from a booster to a seat belt.
Read age guideAll Booster Seat Laws by State
Return to the 50-state laws hub and compare nearby states before travel.
Open laws hubNearby states
Booster seat laws in states that border Washington
Child passenger rules change at the state line. If you drive out of Washington, the neighboring state's rule applies while you are there, so check it before a road trip or a regular cross-border commute.
OregonUnder 2 yrs in a rear-facing child restraint | Properly used child restraint (harness) required until child weight 40 lbs. | Booster required until the child is 8 years old AND the adult seatbelt fits correctly OR the child is 4’9” tallIdahoUnder 7 years
Compare all 50 states · Seen a notice about adults under 5'2" or 5'4"? Read the adult booster seat law fact check.