Confused about what size clothes to buy for your baby? Here's help. Baby clothing sizes are usually based on age: preemie, 0 to 3 months (newborn), 3 to 6 months, 6 to 9 months, 9 to 12 months, 12 months, 18 months, and 24 months. However, one manufacturer's 6 to 9 months may be quite different from another's because there are no standard sizes in the industry. Every brand of baby clothing has its own size specifications. A general rule, "Double your baby's age," says Vivian G. Reisman, president of Baby Steps, a children's clothing manufacturer based in Closter, N.J. For example, if you're buying for a 3-month-old, buy a 6-month-old size; if you're shopping for a 6-month-old, buy a 12-month-old size, and so on. Even though that doubled size may seem a little big at first, your baby will grow into the clothing quickly and you'll have leeway for shrinkage.

You don't always have to double the size, though. It depends on the manufacturer, so experiment. "I've found that some brands, like the Gap and Old Navy, run true to a child's age," says Michelle Dyson, a mother of two, from Boulder, Colo.

The age-doubling formula ends at around age 2 anyway, says Reisman. Then, buy one to two sizes up, depending on your child's size. For example, an average-size 2-year-old (a toddler in the 50th percentile for height and weight) can probably wear a size 3. But a large 2-year-old (say, in the 95th percentile) would wear a size 4, she says.

Read the weight and length charts found on the back of many garment packages or consult a size chart, which many baby-clothing stores keep on hand, especially those that sell garments in European sizes. But be sure to know your baby's height in inches--that's key to converting your baby's size to centimeters.