1T vs. 12 Months – Baby Clothes Sizing Explained

1t size

No one tells new parents the overwhelming experience of figuring out baby clothes sizing.

Plenty of people told me I would never sleep again and I would experience this strange, overwhelming love for my squishy newborn, but not one person told me you need a Ph.D. to determine what size my child would wear.

So, when it comes to 1T vs. 12 months, how do you figure out the difference? There’s a good chance your child will fit in either, but 1T is better suited for babies who have had their first birthday and are starting to run around. On the other hand, 12-month clothing fits babies up until they turn one.

The different clothing sizes can get confusing, especially if this is your first rodeo. Although, even with my third child, I often found myself scratching my head when it came to the right size for her.

I also noticed sizing for boys and girls varied, with girl clothing being much smaller. So, I often had to size up for my daughter while my boys wore what I anticipated.

The most important aspects to consider when buying baby clothes are your child’s weight and height, regardless of their age.

Thankfully, with delivery at our doorstep and big box stores with excellent return policies, you can experiment with different sizes. That said, if you have friends and family asking what size to get for your bundle, it is good to know the difference in sizes.


Is 1T The Same Size as 12 Months?

1T and 12 months are technically different sizes, but with only slight differences. For example, 1T is ideal for babies that are too big for 12-month clothing but too small for 18-month clothing; instead, 1T provides a happy medium for babies.

Generally, 12-month clothing means up to 12 months. Another slight difference is 1T is made for mobile children, while the 12-month size is better for crawling babies. However, 1T generally allows room for a diaper since most 1-year-olds aren’t potty trained. (But, I bow down if yours is.)

However, you don’t always find 1T clothing, so it can sometimes be hard to find the correct next size. Typically, you’ll find clothing in 18-24 months, 12-18 months, and 2T. But, if your toddler is in the smaller size, 1T will likely be the perfect fit.

Also, if the clothing is labeled 12 months, it likely fits a 9-12 month old best. Typically, 12-month clothing fits babies 28-30 inches in height and 20-24 in weight.

A one-year-old’s average weight can vary between 15-21 lbs, meaning your child could easily fit in 12-month clothing if they fit within that range. However, you’ll often find going up one size provides a more comfortable fit if your child falls right on the line of sizes.

Also, babies grow so fast, so it’s best not to stock up too much on one size because it will be too small in no time. So I think once my kids could sit upright, they were never in something for very long.


What Does The “T” in Sizing Mean?

The “T” in children’s sizes refers to toddlers and is ideal for kids who are walking. Toddler sizing becomes more straightforward, although you’ll probably wonder if you need 24 months or 2T. (For the record, a two-year-old would probably fit better in a 2T.)

You also will find different labeling in other countries, like Europe. For instance, European sizing is roughly the same as in the United States, but since they refer to the child’s height in centimeters, the clothing size would be listed as 80cm instead of 12 months.

Therefore, a size 80 will fit a child up to 80 cm in height, or 31.5”. In addition, while sizing charts vary across the board, you often will find baby/toddler clothing in the following sizes.

  • Preemie
  • Newborn
  • 0-3 months
  • 3-6 months
  • 6-9 months
  • 9-12 months
  • 12-18 months
  • 18-24 months
  • 24 months
  • 2T
  • 3T
  • 4T
  • 5T


What Size Does a 1-Year-Old Wear?

A 1-year-old’s clothing size varies based on weight, height, and walking ability. However, baby clothes can be tricky, especially since sizes can vary from one brand to the next.

So, a brand sizing chart is a lifesaver if you struggle with finding the right size for your 1-year-old. For example, a one-year-old baby is likely almost ready to wear an 18-month size and might pop out of a 12-month outfit.

Here’s a sample sizing chart to give you an idea of your child’s size. Remember, this is just an average and doesn’t apply to every brand.

Size Age Weight Length
P Preemie Up to 5 lbs Up to 17 inches
NB Newborn 5-8 lbs Up to 20 inches
3M 0-3 months 8-12.5 lbs 20-23.5 inches
6M 3-6 months 13-16.5 lbs 24-25.5 inches
9M 6-9 months 17-20.5 lbs 26-27.5 inches
12M 9-12 months 21-23.5 lbs 28-30.5 inches
18M 12-18 months 24-26.5 lbs 31-32.5 inches
24M 18-24 months 27-30 lbs 33-34.5 inches


Remember, the perfect fit for baby clothing is not too loose, allowing mobility. It’s also best to pay attention to the different features of baby clothes.

For example, if I could give one piece of advice to new parents, it would be never to buy baby clothing with buttons. Instead, you should immediately put it back on the shelf and pick up the zippered pajamas.

All kidding aside (although, never buy buttoned pajamas), you want to find comfortable, simple clothing for 1-year-olds.


At What Age/Size Does Kids Clothing Stop Using “T”?

You’ll typically find the largest “T” size is 5T, then the “T” is dropped, and you go off the number. However, you will soon learn that toddler sizing varies and you’ll be confused all over again.

For example, some stores have single number sizes (ie: 6, 7, 8, etc.) However, some sizing starts to combine sizes and you’ll notice ⅞, 8/10, 10/12, 12/14, and so forth.

In addition, you’ll also come across some brands that only have even or odd sizes (6,8,10,12, etc.). I am not a fan of this because my almost seven-year-old is too tall for size six but not big enough for size eight.

Finally, when deciding whether an outfit fits appropriately, there are several things to consider, including:

  • Does the clothing leave red marks on your child’s leg, indicating it is too tight?
  • Can your baby comfortably crawl without the clothing interfering with movement?
  • Does your baby seem uncomfortable due to a rough fabric?
  • Do they seem too cold or too hot?
  • Are there clothes too baggy, and you constantly are pulling them up?

While there doesn’t seem to be an exact science of how baby clothing fits due to the various babies’ sizes, it’s safe to say that you’ll likely stop seeing the T on clothing after your child turns 5.

In addition, your 12-month will probably fit best in 1T, as 12-month clothing is sized for babies up to 12 months. However, with the shortage of 1T sizes, you’ll find yourself reaching for 12-18 months more often than not.


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