Booster laws are the one car seat rule that every state has in some form — all 51 states and DC require a child restraint at the booster stage. What differs, state to state, is the age it ends at and which numbers, if any, back that age up.
The age ranges from 5 to 10
Of the 51 jurisdictions, 49 write a specific age into the booster requirement. The other two — Delaware and Washington — don’t set an age at all; their statutes describe the requirement in terms of a height cutoff and, in Delaware’s case, wording about fit rather than a number.
Here’s how the 49 numeric ages break down:
| Age | Number of states |
|---|---|
| 5 | 1 |
| 6 | 5 |
| 7 | 4 |
| 8 | 33 |
| 9 | 5 |
| 10 | 1 |
Eight is by far the most common booster age — two-thirds of the states that set one use it. South Dakota, at 5, is the lowest; Hawaii, at 10, is the highest. That’s a five-year spread for what looks, at a glance, like the same rule everywhere.
Height shows up more often than weight
Twenty-nine states pair their booster requirement with a height cutoff, and 57 inches — 4 feet 9 inches — is the number nearly all of them use. That figure comes from where an adult seat belt starts to fit a child’s body correctly on its own: the lap belt across the thighs instead of the stomach, the shoulder belt across the chest instead of the neck.
Fewer states set a weight cutoff — 12 do, and the numbers vary more than the height figure does: South Dakota’s is the lowest at 40 pounds, while New York’s statute reaches all the way to 100 pounds. Most states that specify a numeric weight pair it with a height and an age, rather than relying on weight alone.
“Whichever comes first” is the normal pattern
In 46 of the 51 jurisdictions, a child leaves the booster stage on meeting any one of the listed limits — the age, or the weight, or the height, whichever is reached first. Texas is a clean example: its statute requires a restraint system for a child “younger than eight years of age, unless the child is taller than four feet, nine inches” — age eight or 57 inches tall, whichever comes first.
A smaller group works differently. Connecticut and New Mexico require all of the listed conditions before a child can leave the booster stage rather than just one — Connecticut’s statute requires a child to be “not under five years of age, or weighing less than sixty pounds,” which in practice means the child needs both the age and the weight. Hawaii and Mississippi go a step further with a compound rule: Hawaii lets a child leave at 10 regardless, or earlier at age 7 and over 57 inches tall — two separate paths, each requiring more than one condition met together. (Article 4 walks through exactly how these combinations get read from statute text, with more examples.)
Two states skip the numbers
Delaware and Washington don’t attach a specific age or weight to the booster requirement. Washington’s statute requires a booster for a child “under four feet nine inches tall” who hasn’t moved on to a seat belt — height only, no age limit at all. Delaware’s booster rule hands the cutoff to the seat itself: a child must stay in the booster “until they reach the upper height or weight limits of the restraint per the manufacturer’s guidelines,” which means there’s no fixed state figure to compare against other states — the limit is whatever the specific booster is rated for.
What this means for a family
A child who has outgrown the booster requirement in one state has not necessarily outgrown it everywhere. A seven-year-old who is done with boosters under a state with an age-6 rule (assuming the weight or height limit is also met) would still need one for another year or two under most states’ age-8 rule, and for three more years under Hawaii’s age-10 rule. The height figure is the more portable number of the two — 57 inches means close to the same thing everywhere it appears — but the age attached to it is not.
Each state’s own booster page lists the exact age, weight and height figures with the statute text and the date they were last verified — that’s the number to use for a specific state, not an average across all of them.