The #1 Baby Gift Mistake (And How to Avoid It)
You found the perfect funny baby onesie. You're ready to buy. Then you see the sizes: 3-6M, 6-12M, 12-18M, 18-24M. And suddenly you have no idea what you're doing.
Don't worry. This happens to everyone who hasn't recently had a baby. Here's the simple guide to getting it right.
The Golden Rule: Size Up
If you take nothing else from this post, take this: always buy one size bigger than you think you need.
Here's why. Babies grow incredibly fast. A onesie that fits perfectly at birth might only be worn once or twice before the baby outgrows it. New parents also receive a mountain of newborn and 0-3M clothing at baby showers — they're often drowning in the small sizes and short on the larger ones.
When in doubt, go 6-12M or 12-18M. The baby will get there faster than you think.
The Soapy Mouths Size Guide
Here's exactly how our onesies fit:
| Size | Width | Baby Length | Baby Weight |
|---|---|---|---|
| 3-6M | 9 3/8" | 20-25" | 12-16 lbs |
| 6-12M | 9 7/8" | 25-28" | 16-22 lbs |
| 12-18M | 10 3/8" | 28-30" | 22-27 lbs |
| 18-24M | 10 7/8" | 30-32" | 27-30 lbs |
What If I Know the Baby's Age?
Age is a starting point, but babies vary wildly in size. A 6-month-old might be wearing 12M clothing, or a chunky 3-month-old might already be in 6-12M. If you know the baby is on the bigger side, definitely size up.
As a general rule of thumb:
- Baby is not yet born or just arrived: Buy 6-12M. Newborn sizes get used up fast.
- Baby is 0-3 months: Buy 6-12M or 12-18M.
- Baby is 4-6 months: Buy 12-18M.
- Baby is 7-12 months: Buy 18-24M.
What If I Want the Gift to Be Worn Soon?
If you're giving the gift at the baby shower and want the parents to be able to use it right away for newborn photos, go with 3-6M. Newborn sizes (0-3M) are often too small even at birth for bigger babies, so 3-6M is the sweet spot for "use it now" gifting.
Just know the window for wearing it will be short!
The Bottom Line
When buying a baby onesie as a gift, 6-12M is almost always the safest bet. It gives the parents time to enjoy it, the baby time to grow into it, and you the satisfaction of knowing it actually got worn.
Now go pick out the funniest one you can find — the parents will love you for it.