Guide to Understanding Infant Onesies by the Month (MONTHSIES)

  • This every parents’ ultimate guide to baby clothes
  • Read about onesies for babies from newborn to 24 months old
  • Learn about onesies for toddlers, too, aged 2T to 6T
  • Plus, handy tips for buying clothes for your children

As parents, we have it hard. From newborn to kindergarten, we constantly need to keep up with our growing little ones. It will probably the hardest job you will ever have because there will be no breaks from it.

At least until they’re finally off to college.

But as our little munchkins grow, we look at our own achievements as well. From learning how to breastfeed to choosing the perfect outfit for any occasion, these are just some of the 'tasks' required of a parent.

Clothing is just one factor. In 2012, a forecast through 2016 was done by Euromonitor International to show sales in baby needs. Clothes had the biggest chunk of household expenses, outstripping food..

In the forecast, comfort and safety is a concern when it comes to clothes and footwear for baby. This goes to show how parents think about safety even in their children’s clothing.

Toddler or Baby?

Sure, you’ve carried them in your womb for 9 months, but are you getting the right size of clothes? It might seem easy, but unfortunately and surprisingly, some moms and dads fail at buying the right clothes for their kids.

Don’t worry. It happens to all of us.

The thing is, it’s not easy. Babies and kids are shaped differently, not to mention their development happens at such a fast pace. What makes this even more confusing is the varying size standards!

Some brands, you will find out, will have a different term for their clothes from the other brand just across. In addition, Europe and the US have different rules on this too!

If this does not stress you out, congratulations! But for some parents, this could be a veritable nightmare.

Nonetheless, some moms and dads still do get confused. In truth, it is really puzzling many. So, are you buying for a baby or toddler?

Some will say that by the time your child passes the one year mark, they become toddlers and no longer babies. But as far as clothing is concerned, these are two different things.

Sometimes, you have those really big babies who come from very tall and large-boned parents, who defy the sizing charts simply because of genetics. How about those babies?

Some parents would bring the baby with them to fit the clothes, but this a new challenge all together. Taking a baby along with you shopping can mean everything from taking the kitchen sink to being able to change diapers and nurse when you’re stuck in traffic.

Unlocking the Baby Clothing Mysteries

This might get more confusing so we would like to lay this out for you one by one. This way, you can just hang this up on your wall or resize it to put in your wallet as a guide when you go shopping.

  • If you have encountered a 2T, 3T, 4T in the baby section and are puzzled by it, there is a simple explanation for this. The “T” in 2T and the like stands for “toddler”.
  • 2T is “almost” the same as 24 months and we will explain in the succeeding tips why.
  • There is no such thing as a “one size fits all” clothes, especially with babies. This means that a 3-6 month old onesie may or may not fit a 3 to 6-month old baby and so on.
  • The 24-month (as goes with the other sizes with “month” or “M” on it) sizes are rounder. This is most appropriate for healthy and growing babies who are still crawling.
  • The 2T (as goes with other sizes with “Ts” in them) sizes are less round and narrower in width but more upright or longer. These are intended for babies who are already walking. These allow for easier movements as your baby begins to explore more than be stationary.
  • The 24-month sizes allow room in the tush, for bulky diapers or snaps in in the inseams.
  • If you will notice, clothes in the 24-month ranges are more baby-like. These are the clothes that are made just for babies.
  • Onesies are the same as bodysuits. Most brands prefer calling it bodysuits because Gerber has trademark rights to the word “onesie”.
  • European and US sizes are different. But some would say that European sizes are more appropriate.
  • European sizing is based on height and are in centimeters rather than in inches.
  • Some manufacturers or brands provide size charts online. These charts start from preemies to toddlers of different ages. In some instances, they even provide height, weight, chest, waist and hip sizes.
  • When no age or month range is included, it means the maximum age range. Twenty four months is really 18 to 24 months.
  • You will still encounter zeros, Xs and the traditional small, medium, large size labeling.
  • In other cases, manufacturers or brands will have different sizing for different types of clothing. For example, different size structure for gowns, dresses and sleepwear.

Month by Month Onesies Guide

Don’t know what clothes to get for a baby? Here is a monthly guide and recommended sizes for onesies you can get for a baby.


Premature babies or preemies are obviously small--even more so than newborn infants. They typically weigh 2 kilograms or even less. The most appropriate would be the smallest onesies.

Preemies need special care, so clothes that take this into consideration is a boon.

Choose a onesie that has Velcro fastenings so it is easier to attend to their needs without having to undress them. Some brands even have onesies that are designed in conjunction with neonatal care units.

More specifically, preemies that weigh up to 2.26 kilos and are up to 43 centimeters long can make use of the special preemie onesies.

However, if the brand you chose does not have a onesie specific to a preemie, you can always get the 0 to 3 months onesies.

Newborn Onesies

Newborn onesies are in the zero to 3 months range. But to be exact, you can use the 2.2-3.6 kilos range to act as your guide. Newborns, with the exception of the preemies, need the most delicate care you can give, that includes their clothes.

You don’t want them too big or too small as this might prove a health hazard.

3-6 Months Onesies

A 3-6 month onesie is estimated to be for a baby that weighs 3.6 to 7.4 kilos. In terms of height, it is most appropriate for babies of 55 to 67 centimeters. Onesies 3-6 months should not be mistaken for 3T onesies, though.

6-9 Months Onesies

If you feel frustrated about baby clothes, don’t be, as you’re not alone. Don’t be surprised too that you’re in the market again for clothes so soon – after six months to be exact. It may seem such a long time, but time flies. One minute you were fussing over 3-6 month onesies, the next you’re shopping for 6-9 month onesies.

When you shop for 6-9 month onesies, look for those within 5.7 to 9.2 kilos range when it comes to weight and 61 to 72 centimeters in length or for the height.

9-12 Months Onesies

By the time your baby hits the 9 to 12 month milestone, you would have been more comfortable choosing clothes for your child. You will also feel more excited because he or she would have learned or learning to sit upright or walking.

You will then be more conscious of your choices. Parents even choose baby month onesies for monthly photo shoots. Whatever design you choose, be guided that babies in this age range commonly weigh 7.4 to 11.1 kilos and 67 to 78 centimeters in height.

12 Months Onesies

In 12 months or your child’s first year, you will be busy with their first birthday party. On another note, babies in this age can use 12 month onesies.

These onesies are really for 12-18 month old babies. These are babies weighing from 9.2 - 12.4 kilos and 72 - 83 centimeters in length.

18 Months Onesies

At 18 months, your baby will be in active mode, making you run around as you chase them around the house or outdoors. At this time, babies are thirsty for activity.

Make sure that they are comfortable in just about anything that they are doing--be it walking, running, tumbling on the cushions or at rest (though that’s nearly impossible!).

Those 18 month onesies are still the best gear for your baby. Not only do they provide no hassle when it comes to their daily quests for adventures, they are well protected as well when they feel that they have had enough adventure and are ready to take that nap or sleep at nighttime.

Remember to choose cool, absorbent material to keep your baby from getting rashes from sweat and heat.

24 Months Onesies

Congratulations on your baby’s 24th month milestone! Babies can both be sweet while being daredevils at the same time. It is also at this time that others will call your babies, toddlers.

At this stage, toddlers start to get interested in potty training. This can be messy as well as life changing for your little one. Like in the early months, your toddler’s mode of clothing is very important for both of you.

Again, it should be comfortable enough for your toddler to move around, while easy enough for you to help him go about potty training. Any 24 month onesies are just the thing. Because it is familiar clothing, your toddler may even be knowledgeable enough to take the lead in unsnapping.

However, if they are not, that is also fine because you can always help them easily through unsnapping and allow them to do their business.

Progressing to Bigger Things

At 24 months or 2 years old, this will be a turning point in your child’s development. Cognitive and motor skills will be coming in fast or slow. After all, babies are built differently.

Believe it or not, clothing will depend not just on one developmental pattern alone. As we mentioned, it will take different factors to finally get the hang of choosing the right clothes for your little tykes.

Other mommies and daddies will still be dependent on baby monthly onesies. But some will move on to toddler onesies 3T. This is entirely up to you and how you know your baby’s capabilities. However, if you have not moved on to toddler onesies, do not be dejected.

Other parents will feel crestfallen that their kids aren’t built like other kids because of this. Know that each child will achieve their milestones on their own when they are ready (but of course, if you feel uneasy, a trip to the pediatrician won’t hurt.)

Baby months onesies are still used in the latter years because of its simplicity, which is everything that either a shy or active child needs.

To remove confusion, monthly onesies can also mean 2T onesies until 6T onesies. It just means they are translated into years instead of months, so these are for 2-year-olds and 6-year-olds respectively.

Let’s move on to more detailed description of the toddler sizes.

Toddler Onesies

Once your baby becomes a toddler, clothing options expand. You can try brighter colors, cuter designs and thicker fabric. You have to consider shoes, since they’ll probably be walking around the house.

Aside from that, you also have to think that bodysuits aren’t your only option anymore. If you’re potty-training, these clothes can be either a help or a hindrance to teaching your child to “go” on their own.

To help you out, here are short guides for each clothing size for onesies (and other baby clothes) once your child hits toddler years:

2T Onesies

2T onesies can be translated to 24 months if you decide that your child is still a baby. But as described, if your child is potty trained and already up and running about, then you can gladly say that he or she has grown into a toddler. When picking out clothes always remember this consideration.

On the other hand, you can also be a bit more specific by choosing by measurements. 2T onesies are for toddler who are between 13-14 kilos, and are 88 to 93 centimeters tall. Some brands offer charts in their stores so this shouldn’t be a problem.

3T Onesies

3T onesies are for children in the 13-15 kilos range and are 91-97 centimeters tall. You will hardly find a clothing store though that will translate 3T in months, so don’t be surprised. Most manufacturers just got used to the standard of following the the “T” label once children hit 3 years old.

This is also the perfect time to say, “Congratulations! You’ve passed the ‘terrible twos’ stage!” You can now breathe easier and actually enjoy shopping for your baby more.

4T Onesies

By 4 years old, you will be talking about going to school now. This is expected so you also gear up for it. Your 4 year old’s 4T onesies are even more essential as she learns continues to learn about independence.

Your child will be more mobile but careful of her movements at the same time. This is because along with her motor skills, her cognitive skills are also on the move.

With this, buy your child onesies that are in the 15-17 kilos and are 99-104 centimeters tall.

5T Onesies

It isn’t a secret that you will be buying lots of clothes for your kids. Honestly, they just grow up too fast! This may seem like a chore to others, but by this time, you’ll be more confident in shopping. In addition, you might be getting a lot of help from your child by now.

Colors and shapes will play a big role in their choice.

So, don’t stress about it and involve them. Your role will be in making sure that the clothes are appropriate and comfortable.

Of course, your job is also to make sure that their choices will fit. You may need to look at different size guides now. For a 5 year old, 5T onesies should be 16.78-19 kilos and are 104.14-109.22 centimeters tall.

A word of caution though that 5T and 5, as you will later on encounter are still different. They may be the same in weight range but they differ in height range.

6T Onesies

When your kids hit the 6 year old mark, you will rarely see 6T onesies. Most will drop the letters and stick to the numbers. Brands will also separate measurements for boys and girls. If this is the case, you can still use the majority’s standards by knowing the specific ranges.

For this, you will see a 6 which corresponds to 19.5-221.77 kilos and 111.76-116.84 centimeters. Let’s cover all the bases and include the chest, waist and hip sizes. Size 6 also means 60.96 centimeters for the chest, 55.88 centimeters for the waist and 63.5 centimeters for the hips.

Tips on buying your child’s clothes

Size shouldn’t be the only consideration when you’re buying clothes for your children. They may have a health condition or require thinner or thicker garments. You might also want to look at colors and designs.

Tips and tricks to keep in mind when buying your baby clothes:

1. Most importantly, sizes on charts are just guides. It is still up to you to decide which will be more appropriate and comfortable for your child.

2. When in doubt, opt for a larger size. By buying a larger size, they will eventually get to wear them unlike if it is too small. Be conservative and give ample room for growth (and wiggle room!).

3. Comfort is more important. You might be tempted to go for the stylish ones, but this may prove irritating for your baby. On another note, some clothes trigger allergies or tantrums. The more comfortable, the better for your baby and for you too.

4. Don’t limit yourself when it comes to colors, nor should you push a color to a specific gender. Open yourself up to different perspectives. Not all baby girls would want to wear pink. For all you know, the little girl would want variety. Same with baby boys and blue hues. When you limit yourself to labels, you also limit your child. So, explore the different colors of the rainbows!

5. Onesies are best for babies especially for the earliest months. Separates get in the way of the waistband and might infect or irritate the umbilical cord.

6. For younger children, light-colored or white bodysuits are usually the best option since it’s easier to spot dirt, redness, an insect or other small undesirable objects on your baby.

7. Consider care and washing instructions. It’s better to get plenty of the same type of fabric and color so washing and ironing your baby’s clothes aren’t too much of a hassle.

8. Consider embroidery and such when you’re choosing your baby clothes. You may want to monogram your baby’s initials onto the clothes, so see if the cloth is thick enough for new stitches.

9. Natural fiber such as cotton is the most appropriate. Babies have sensitive skin, so other types of fabric can irritate even with the slightest contact. In worst cases, it can even trigger allergic reactions. So if you’re tempted to get that satin, sheer and tulle getup, think again Mommies!

10. Onesies are essential clothes. They’re just right for any weather, especially during the humid seasons. But when the winter season sets in, all you need to do is double up with another layer of clothing such as a jacket, sweater or anything that can increase the heat in the body.

11. Plan for the weather. Thick bodysuits may be more appropriate if you live in places where it gets very cold all the time. But if your area experiences more sun, consider getting suits without hoods that are also thin and cool.

12. Small is cute. But you won’t think so if you need to take it off of your baby. Babies naturally don’t like things rubbing on their skin. Any slight contact sets off a crying spit.

When they cry, it gets even harder to remove their clothes. So when shopping, think of how to take the clothes on and off of them. Will it be a breeze to take the garment off, or with a little tugging, a lot of pulls, scratches on the head? These are the questions you need to answer before settling on a specific design.

Another thing you have to consider is that bodysuits are easier to grow out of. Your child may suddenly become taller, and the bodysuit may not be comfortable after a month.

At times, you will even need to simulate this process in your head while shopping, so you don’t encounter any problems and end up wasting money on clothes you babies or kids don’t want.

Some general thoughts on all baby clothes:

1. Elastic waists on pants rather than button fly like adults have are better for kids. Unless your child is big enough to manage things on their own, getting a pants with an elastic band is easier, again for both of you.

2. Think of the time you need to take it off when they need to go to the bathroom or you need to change diapers on the go! You don’t ever want to end up with soiled pants and a cranky baby on the way.

3. Color is good, but white clothes are simply the best. White is associated with cleanliness. However, because of a child’s activities, they seem to attract dirt like honey to bees. You would want to spot those specsk, splashes and whatnot early on so bacteria will not settle. Whites are especially suitable for these types of scenarios.

All in a Mom’s Day’s Work

No doubt about it, being a parent is the hardest thing ever. But it is also the most rewarding, as you will hear most mom and dads say. There are a lot of things to think about—clothing is just one factor.

It is surprising that such a small person would have a lot of needs. Even more compared to adults like us. But clothing is just a part of every parents’ day’s work. It is something that you cannot skip on, so to speak.

However, amidst all your frustrations over clothing sizes and designs, know that things get better as your child grows. Having them choose their own clothes with you is one of the most enjoyable ways to bond with them. So, lose the frustration and just continue to treasure this phase in your children’s lives. After all, they’re only kids once.

Bonus Video

You Might Also Like