An infant car seat only faces the rear of your car, is suitable for babies up to 16kg or 18kg and 80cm to 88cm tall, and fits babies snugly during the first year or so.
A convertible seat – so called because it converts from a rear-facing seat for babies and toddlers to a forward-facing seat – carries children from birth to somewhere between 18kg and 36kg and up to 144cm tall, depending on the seat.
A 3-in-1 or all-in-one seat is designed to carry a child from infancy until he no longer needs a booster. It can hold an infant rear-facing from about 2kg to 22kg; forward-facing in a harness from about 9kg to 36kg; and forward-facing as a backless or high-backed booster with a maximum weight of 36kg to 54kg and a maximum height of 130cm to 144cm depending on the model.
Given the option of a convertible or all-in-one car seat, why bother with an infant seat?
The most important reason is safety. Although most newborns fit in a convertible or all-in-one car seat, experts generally agree that infants under 9kg are best secured in an infant car seat.
A convertible seat's harness straps may be too long to get them tightened correctly for a baby, or the harness slots may be positioned too high. When rear-facing, the harness shoulder straps should emerge from the car seat at or just below your baby’s shoulders for proper protection; if they're too high, they will be above your baby’s shoulders.
Convenience is another big consideration. Infant car seats are smaller and lighter than convertible or all-in-one car seats and usually have a handle for easy carrying. They snap in and out of a base you install in the car, and in and out of your stroller, so you can transfer your baby from place to place without waking him. In contrast, most convertible and all-in-one car seats must be installed in the car. Plus when you reach your destination, you have to unbuckle your baby and transfer him to a stroller or other carrier.
A final consideration: Newborns should ride at an angle of about 30 to 45 degrees to provide optimum crash protection without interfering with breathing. Some convertible car seats will take up a lot of space back-to-front when installed at this angle, which may force the car’s driver or passengers to pull up their seats uncomfortably; there may not even be enough room for drivers/passengers with the seat installed at the correct angle.
Once a child outgrows an infant seat, you'll have to buy a convertible or all-in-one model. Larger babies may outgrow the seat long before age 1, while smaller babies may fit in it until their 1st birthday or beyond. (Babies tend to exceed the height limit for an infant car seat before the weight limit.)
The attached video is US based but it applies to worldwide standards when purchasing a car seat. Do the right thing and buy the best for your child to keep them safe! All Car seats on our site are SABS approved and Internationally approved.