Recently, several parents have asked me how much their child should weigh before they use a booster seat in the car. This is a complicated question! The answer can be different based on the child, the car seat, and your state's laws.
Check the Booster Seat
First things first, you need to know what the minimum weight is for the booster seat you want to use for your child. Booster seat manufacturers are required by federal law to clearly state the lower and upper weight limits for each seat.
This information can be found on the labels on the sides of the booster seat, as well as in the instruction manual. If you're using a combination car seat that can be used with a harness or as a booster with the seat belt, be sure you're looking at the weight limits for just the booster seat portion. The weight limits for the harness will be different, and they will be listed separately.
Once you know the lower weight limit for the booster seat, you should definitely follow it as you decide whether or not your child is ready for the booster seat. Some booster seats can be used with children who weigh as little as 30 pounds. Most have a lower limit of 40 pounds. The manufacturer has tested the booster seat to ensure safety, but if your child doesn't fall within the correct weight range on those labels, it may not be able to properly protect your child in a crash.
Remember that there are many convertible car seats that can accommodate a 30-pound child in a rear-facing position, and a 40-pound child in a forward-facing harness.
Just reaching those weights isn't an automatic indicator that a booster seat is necessary, even though there are booster seats available at those minimum weights.
Check Your State Law
Every state has its own car seat and booster seat laws. Take a peek at your state's car seat laws to see if it has specific requirements about age or weight for booster seats.
It's more common for states to have a minimum age for booster seat use, but since each state is different, you need to be sure there isn't a weight requirement, as well.
Many states also have a clause in their car seat and booster laws that says you must use the booster seat according to manufacturer's instructions. That means if you're using the booster seat outside of the manufacturer's stated minimum or maximum weights, it is illegal in a state with a proper use law.
Check Your Child
Once you've determined what the booster manufacturer and your state law say about the right weight for a booster, you need to look at how your child fits in the seat. Remember, if your child can still safety sit in a car seat with a harness, and meets the weight and height limits for the harnessed car seat, that is the safest option! Every step up in car seats is a step down in safety. The 5-point harness spreads crash forces over a larger area of your child's body than the seat belt does with a booster seat. Also, the higher, deeper sides of most harnessed car seats can protect your child from flying debris and can reduce side to side movement in a side impact crash.
Children who ride in booster seats should also be able to sit properly in that seat for the whole trip.
The weight limit is only one piece of the puzzle. If your child unbuckles the seat belt or moves it out of position, a booster seat may not be a good idea for now.