The "Best" Car SeatAs with any other car seat, a convertible car seat sold in the U.S. must meet federal safety standards and is crash tested to those standards, or beyond, depending on the manufacturer. While some car seats may be more convenient for you than others, they all meet the same basic safety standards. The best car seat is the one that fits your baby and your vehicle, and that you can use correctly every time.
Weight LimitsConvertible car seats have two sets of weight limits. There is a lower and upper weight limit for rear-facing, and a lower and upper weight limit for forward-facing. If you've used an infant car seat until your baby weighs 20 pounds or more, you'll probably want to look for a convertible car seat with a higher rear-facing weight limit to increase the time you can keep baby facing the rear. Most convertible car seats today can be used rear-facing to at least 30 pounds. There are also many models that can be used rear-facing to 40 pounds or more.
The forward-facing weight limit also can determine how long you might be able to use the car seat. Every convertible car seat sold in the U.S. can be used forward-facing to at least 40 pounds. Again, many models go well beyond that limit, with a few convertibles topping out at 70 or more pounds. Your child is unlikely to be ready to move to a booster right at 40 pounds, since young children tend to wiggle out of position easily, so a car seat with a higher harness weight should give you some extra harness time until your child is better prepared to sit still.
Height LimitsThe height limits of your convertible car seat are just as important as the weight limits! Manufacturers will list the maximum heights for rear-facing and forward-facing, but you should also watch how your baby fits in the seat to determine when it's time to switch directions or buy a bigger seat. For rear-facing, the harness slots need to be at or below baby's shoulders, and there should be at least an inch of the car seat shell above his or her head. For forward-facing, the harness slots need to be at or above baby's shoulders, and the tops of his or her ears should be below the top of the car seat shell.
A taller car seat shell and higher harness slots will give you the longest usable time. Take a measuring tape with you as you shop, so that you can measure the differences between harness heights and shell heights on various car seats.
Convertible Car Seats for NewbornsMany parents prefer to use an infant-only car seat for their newborn. However, you can start out with a convertible car seat for a newborn as long as your baby fits the car seat properly. That means your baby must weigh enough to meet the minimum rear-facing weight, and should be tall enough so that the lowest harness slots are at or below his or her shoulders. My 8.5-pound newborn fit just fine in a convertible car seat. However, my under-6-pound newborn did not.
Some convertible car seats come with infant padding to take up some of the space in a large shell and help small babies fit the harness better. If this padding came with the car seat, it's fine to use it according to manufacturer's instructions. If your baby doesn't fit properly in the convertible seat as a newborn, don't add extra padding or accessories to the seat. Use a smaller infant-only car seat until your baby grows a bit.