Infant car seats are designed to be lightweight and portable. Parents can detach the seat from a base they leave in their vehicle and carry it using the attached handle or pop it into a stroller frame for easy transportation outside the car. Most infant car seats are approved for babies 5 pounds and up and have weight limits around 30 pounds, though some may have higher or lower capacities. Height limits usually range from 29 to 32 inches. Seats with higher height and weight limits buy parents extra time before they have to think about switching car seats, but they're often heavier to carry. Also remember that infant car seats are only meant for use rear-facing.Convertible
Convertible car seats are heavier than infant car seats and are designed to stay put in the car. They can be used rear-facing for smaller children and forward-facing for older children. Many convertible car seats can accommodate children up to 40 pounds or more rear-facing, and 65 or 70 pounds forward-facing. Height limits vary widely among seats, but common rules include that rear-facing children have at least an inch of seat shell above their head and that forward-facing children's shoulders must be lower than the top slot used for the harness strap. In general, seats with taller shells have the longest life span, but they often hog more front-to-back room in a car. In addition, seats that accommodate bigger children are among the most expensive convertibles -- but the investment may pay off if you don't need to buy another seat before your child can use a booster seat, which we cover in a separate report.Compact Convertible
For parents used to infant car seats, the sheer bulk of convertibles can be a shock -- especially when they end up hogging half the backseat. Compact convertible car seats are designed with smaller frames, which can be especially useful if you need to fit two or three car seats in one row or must install a convertible car seat in a car where legroom is already limited for the driver or front passenger. But beware: A seat billed as compact may not save front-to-back room even if has a narrow width, or vice versa. Some compact seats have lower height and weight limits, meaning they won't last as long. They also may feel confining for bigger kids.