How Baby (and Kid) Sizing Works

Baby labels are sometimes marked with one number, and sometimes for a range.  When I was pregnant, I got a lot of hand-me-downs and gifts, and missed being able to use some of them because it took someone telling me that the number was the end of the range, not the beginning.  Oy!  To save you some confusion, here is how it works:

• Preemie Size: These tiny clothes are for under about 6 pounds.
• Newborn Size: This is for smaller babies, usually under around 8 pounds.  Some babies skip this size entirely, though both my babies (6 lb 10 oz and 6 lb 2 oz) wore this size for a month.
• 0-3 Months (aka "3"): this is the next size up, although there is often overlap down.  
• 0-6 Months: some items are sized in this huge range, though they are usually items like socks and booties.
• 3-6 Months (aka "6")
• 6-9 Months (aka "9"): Some brands skip this size entirely, so when your baby hits 6 months, don't forget to also use the 6-12 month clothing.  I found the arms too long in the 6-12 month when my babies were at the beginning of this range, or the bodies too wide.  So I really liked the items that came in this often overlooked size.
• 6-12 Months (aka "12")
• 1T: slightly larger than 6-12 months but fairly uncommon.  The "T" in the sizing means it is the start of the size range, not the end.
• 12-18 Months (aka "18")
• 18-24 Months (aka "24"): Some toddlers can skip this size, because it is SO similar to 2T.  The neck holes are a bit tighter and pants a bit shorter, though.  My elder son hit this size in the summer, so shirt length wasn't as important to us then, though.  A friend of mine with a big baby (non-walker at the time) had him in this size and said it was different than 2T. My guess is because he was sitting at the time instead of standing.
• 2T: This is for 2-3 years of age.  
• 3T: This size didn't do us much good, either, but my older son is around the 70th percentile.  He went right from 2T to 4T.  Had we stopped at 3T (which we did for a few items), we would have found the rise of pants very close to 2T in size, but the length longer.  The shorts are also a bit longer, but 4T are not that much longer that it is worth getting a 3T wardrobe in tops.  I think 3T is when manufacturers stop adding extra space for diaper butt.
• 4T: For ages 4-5.
• 5T: The last "T" size.
• XXS: Some brands have this, and it overlaps with 4T.
• XS: Overlaps with 4-5, though slightly longer in the arms and legs, and torso length.
• S: Ages/ sizes 6-7
• M: Size 8
• L: Sizes 9-10
• XL: Sizes 11-12
• XXL: Sizes 13-14

There it is.  Don't forget to try the smaller and larger clothing regardless of what the tag says.  We had a 3T hand-me-down that fits the 6-12 mo range!  

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