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Baby clothes sizes: What you need to know

From tiny jeans and flowered tights to knit caps and adorable PJ's, buying clothes for your baby is super fun. But determining baby clothes sizes take a bit of practice. Choosing the right fit means a comfier baby and a happier parent! Baby clothes sizes are generally determined by length and weight, so take these measurements into account when shopping.

"In general, you'll want to buy clothes that are one size ahead of your baby's age. This way, there's room to grow into the item," advises Dr. Eileen Kennedy-Moore, a psychologist, mom to four kids and the author of "What About Me? 12 Ways to Get Your Parents' Attention Without Hitting Your Sister."

Here's what you need to know about dressing your baby at each age and stage:

Infants: 0 to 6 months

It's all about dressing and undressing at this age. "Between drool, spit-up and diaper leaks, you'll be changing your baby's clothes a lot. So make it easy on both of you and choose shirts with wide necks and loose armholes," says Dr. Kennedy-Moore. At night, sleep sacks with elasticized bottoms are easier than PJs with a dozen snaps around the legs.

You'll also want to stock up on onesies at this point. "These items are comfortable to wear and have a bit of stretch to them," says Stevens. You'll know it's time for the next size when his onesie fits snugly and he has a bit of trouble straightening out his legs.

Bigger babies: 6 to 12 months

Look for pants and shirts with simple fasteners or no snaps at all. Elastic waistbands or baby leggings are ideal. Shirts with button fronts are tough to manage with a squirmy baby, so wait until she's much older for these. A winter coat or jacket with a simple zipper is fine (a hood adds warmth) or think about an easy-to-wear, zip-up snowsuit. All-cotton clothing and layers will work to keep your baby comfortable.

"Sweating can lead to rashes on a baby's sensitive skin, so don't overbundle him," says Dr. Kennedy-Moore. And while socks seem sweet, bigger babies tend to kick them off. Consider footie outfits or booties with adjustable Velcro to keep them secure.

Toddlers: 12 months and up

Older babies are crawling and toddlers are ready to cruise and walk, so pick durable clothes that can tolerate these new moves. At this stage, you can move to denim and corduroy, as these are tougher fabrics that can withstand hours of crawling on carpets and wood floors. Toddlers are a curious bunch, so avoid buttons, which can become loose (and pose a choking hazard) and forego scarves or long drawstrings on hoodies and jackets, which could strangle a baby if they become caught.

Use this chart, based on labels from several major retailers, to gauge the right baby clothes sizes for your tot:

Baby clothes sizes

  • Newborn
    Weight: up to 7 pounds. Length: up to 19 inches
  • 0-3 months
    Weight: 7-12 pounds. Length: 19-23 inches
  • 3-6 months
    Weight: 12-16 pounds. Length: 23-25 inches
  • 6-9 months
    Weight: 16-20 pounds. Length: 25-27 inches
  • 6-12 months
    Weight: 17-22 pounds. Length: 27-29 inches
  • 12-18 months
    Weight: 22-27 pounds. Length: 29-32 inches

It's difficult to predict how your baby will develop, so buying clothes ahead of time doesn't always make sense. Growth spurts occur, and some babies are born big and only last a few weeks in the newborn size. Don't buy too much too early. Also, note that there can be some variability in sizing among manufacturers and retailers.

Read next: Baby shoe sizes: What you need to know

Jennifer Kelly Geddes is a New York-based writer and editor who specializes in parenting, health and child development. She's a frequent contributor to Care.com and the mom of two teen girls.

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