What’s the Average Baby Weight at Birth?

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One of the first facts you learn after delivering your baby is how much she weighs at birth. This information helps the healthcare provider assess your little one's health and development, especially when the weight is tracked over time. Read on to find out what the average baby birth weight is, the average baby weight by month in the first year, and how your baby’s weight is tracked.

Average Baby Birth Weight

Full term babies typically weigh between 5 pounds 11 1/2 ounces and 8 pounds, 5 3/4 ounces at birth.

Eighty percent of full term babies are born within this range. Those born above the 90th percentile are considered to be “larger” babies and those born below the 10th percentile are considered “smaller” babies. Read more above baby weight percentiles to help you understand which percentile your little one is in.

Being on the smaller or larger side at birth is not necessarily a sign of a problem, but your baby’s healthcare provider will watch carefully during the first few days to make sure everything’s OK and that any medical or developmental issues are diagnosed and addressed.

It's worth remembering that babies come in lots of different shapes and sizes, and that each newborn is unique. Your baby’s birth weight may not indicate how big-boned or petite, tall or short, muscular or lean your child will become as an adult. Although you’ll have to wait and see what she will look like as an adult, you may already have some clues: Typically, a child’s build will come to resemble that of the biological parents.

Factors That Can Affect Your Baby’s Birth Weight

Here are just some of the factors that can affect your baby’s birth weight:

  • The length of the pregnancy. Your baby may be bigger if she was born on or after her due date. Babies born earlier than their due dates, particularly if they are born preterm, may be smaller.

  • Genetics. If you or your partner is tall or large-boned, your baby may be a little larger than average at birth. The same goes if you or your partner are short or petite: Your baby may be smaller than average at birth.

  • Birth order. If this is not your first baby, she may be larger at birth than your older child was.

  • Gender. Girls tend to be slightly smaller than boys at birth.

  • Your health. Your baby may have a lower birth weight if you had high blood pressure or heart problems during your pregnancy. If you had diabetes or are obese, your baby may be larger. Smoking cigarettes, consuming alcohol, or taking illegal drugs during pregnancy can also affect birth weight.

  • A poor diet during pregnancy. Gaining a lot of weight over the course of your pregnancy may mean your baby is born bigger. On the other hand, being malnourished during pregnancy may lead to your baby to having a lower birth weight.

  • Your baby's health. Your baby’s size at birth can also be a reflection of any underlying medical conditions, including some birth defects and some infections.

  • Ethnicity. Your ethnicity may also play a role in your baby’s birth weight.

  • If you’re pregnant with multiples. If you have twins or more, your babies may be on the smaller side.

“Larger” Babies at Birth

If your baby is born on the larger side, in some cases he may need extra medical care. For example, if you had gestational diabetes during your pregnancy, your baby may be large and may need an IV drip or extra feedings to help keep his glucose levels stable.

Larger newborns are also more likely to have suffered an injury during delivery, are more susceptible to having jaundice, and are at an increased risk of having feeding difficulties early on.

Your healthcare provider will pay attention to these potential risks and will take the necessary steps to ensure your baby does well.

“Smaller” Babies at Birth

If your baby is born on the smaller side, her temperature, glucose levels, and hemoglobin levels may be closely monitored by her healthcare provider.

Your baby may need a longer stay in the hospital, depending on how small she is. Your child’s healthcare provider will be able to make an assessment about when she’s ready to go home.

Preemies

Preemies spend less time developing in the womb and often have a lower birth weight than full term babies. How much the average preemie weighs depends on how many weeks early he was born.

When it comes to preemies:

  • Low birth weight means your preemie weighs less than 5 pounds, 8 ounces at birth

  • Very low birth weight means your preemie weighs less than 3 pounds, 5 ounces.

If your baby was born prematurely, remember that he will be getting extra attention and expert care, possibly in the Neonatal Intensive Care Unit (NICU), where a healthcare team will be monitoring all aspects of his health and development, including his growth.

Why Your Baby’s Weight Is Important

During your baby’s first year, and beyond, your child’s weight gives his healthcare provider one indication of whether there are any medical or development issues, and whether your little one is getting enough (or too much) to eat.

Although a single weight measurement can offer valuable information, your baby's healthcare provider also wants to see how your baby grows over time. For example, if your baby is growing at a steady, predictable rate during the first six months but then suddenly starts growing at a slower pace, the provider can start to look into why that may be happening.

If there is any issue, your provider will be able to make a diagnosis and recommend a course of action.

Keep in mind that when it comes to weight there is a broad spectrum of what’s healthy and normal. Your baby gaining weight steadily is more important than how much your baby weighs at any given time compared to others. Trust what your healthcare provider tells you about whether your baby is on track.

Newborn Weight Loss

During the first few days after birth, your baby may lose a few ounces (possibly about 7 to 10 percent of her birth weight) as she sheds some excess fluid. Your little one will likely regain this weight within about two weeks.

It's good to know that even healthy babies may have periods later on when they don’t put on weight, or gain very slowly, or even lose a little weight, particularly if they’ve been sick, but generally speaking the trendline should be upward to ensure your baby’s overall health. If you’re in any doubt about your baby’s weight, it’s safest to contact her provider for a checkup.

Growth Spurts

There may also be occasional growth spurts during your little one’s childhood. For example, your newborn might grow rapidly at about 7 to 10 days and again between 3 and 6 weeks. During these growth spurts, you may find your baby is hungrier than usual and may want to be fed more often or for longer stretches at a time. These periods of increased feedings are sometimes called cluster feeding.

Whether your baby is formula-fed or breastfed can also impact the pattern of weight gain as well as when growth spurts occur.

For example, breastfed babies may gain weight more slowly than formula-fed babies, and formula-fed babies may gain weight more quickly after 3 months of age.

Baby Weight Percentiles Explained

When it comes to your baby’s weight, percentile is the term used to describe where your child fits compared to other babies of the same age and gender. As an example, if your baby is in the 50th percentile for weight, 50 percent of babies of the same age and gender weigh less and 50 percent weigh more.

The higher the percentile is, the bigger your baby is compared to others of the same age and gender; the smaller the percentile is, the smaller your child is.

To track what percentile your baby is in, during the first 2 years your baby’s provider will plot your baby’s weight on growth charts like these:

On baby growth charts, percentiles are marked by curved lines that depict a steady and predictable rate of growth over time. There’s no one ideal percentile to be in; rather, the goal is for your child to show a fairly predictable pattern of growth.

Here are the percentiles typically shown as curved lines on growth charts to give you an idea of what they mean:

  • 2nd percentile. Your baby weighs more than 2 percent of babies of the same age and gender, and 98 percent of babies weigh more.

  • 5th percentile. Your baby weighs more than 5 percent of babies of the same age and gender, and 95 percent weigh more.

  • 10th percentile. Your baby weighs more than 10 percent of babies of the same age and gender, and 90 percent weigh more.

  • 25th percentile. Your baby weighs more than 25 percent of babies of the same age and gender, and 75 percent weigh more.

  • 50th percentile. Your baby weighs more than 50 percent of babies of the same age and gender, and 50 percent weigh more.

  • 75th percentile. Your baby weighs more than 75 percent of babies of the same age and gender, and 25 percent weigh more.

  • 90th percentile. Your baby weighs more than 90 percent of babies of the same age and gender, and 10 percent weigh more.

  • 95th percentile. Your baby weighs more than 95 percent of babies of the same age and gender, and 5 percent weigh more.

  • 98th percentile. Your baby weighs more than 98 percent of babies of the same age and gender, and 2 percent weigh more.

Healthy, well-fed babies typically gain weight at a predictable rate, meaning that if they weigh in at the 50th percentile at 2 months old, they will likely still be in the 50th percentile at 6 months old. However, as mentioned above, there are occasions when your child may not grow at the expected, steady rate.

Keep in mind, your baby’s weight will be checked against her age, as well as against her length to check she is growing proportionately.

Average Baby Weight by Month

There’s no single average baby weight in the first 12 months that’s relevant for all babies and all families. As you’ve read above, what's key is that your baby gains weight steadily based on her own growth rate. A baby who’s in the 50th percentile is not necessarily any healthier than a baby in a lower or higher percentile.

As a general guideline: During your little one’s first month, your baby may gain about 1 ounce per day on average. Then, your baby may double her birth weight by 5 or 6 months of age, and triple it by 12 months.

As your baby’s weight changes, you may need to go up a diaper size. Check out this Pampers size and weight chart to make sure you choose the best diaper size for your baby.

When Is Your Baby’s Weight Checked?

Your baby’s first weigh-in will likely happen soon after birth. Then your baby’s pediatrician will be checking your child’s weight and other measurements like length and head circumference at each well-child visit. In the first year, these are the times and ages when the well-child visits are typically scheduled:

You’ll likely be asked to undress your baby for the weigh-in, so make sure your baby is dressed in clothes that are easy to take off and put back on.

What to Do If Your Baby Is Gaining Too Much or Too Little Weight?

A healthy, well-fed baby tends to gain weight (along increasing her length and head circumference) at a steady, predictable rate. Although a different pattern may not always indicate a problem (a growth spurt could be responsible, for example), if your baby falls outside of what’s expected for him, your child’s provider will consider whether a developmental, medical, or feeding issue may be at play.

To get a complete picture, beyond checking your baby’s growth, your provider may also ask you

  • how many feedings your baby has per day

  • how much your baby eats per feeding (for breastfed babies your provider may ask whether your baby seems content after a feeding)

  • how many wet diapers you’re changing a day

  • how many bowel movements your baby has each day and what the consistency of the baby poop is.

Once a diagnosis is made, your child’s healthcare provider can recommend a personalized treatment plan based on what is causing either too little or too much weight to be gained.

FREQUENTLY ASKED QUESTIONS

  • At birth, babies weighing over 8 pounds, 5 3/4 ounces are considered to be bigger babies.

  • At birth, babies weighing over 8 pounds, 5 3/4 ounces are considered to be larger babies.

  • At birth, 80 percent of babies weigh between 5 pounds 11 1/2 ounces and 8 pounds, 5 3/4 ounces.

The Long and Short of It

Your baby’s weight is a significant piece of information for her healthcare provider, as it helps the provider check that she is growing well. Still, try not to fixate on the number or compare your baby’s weight to that of other babies. There’s a broad range of weights that are considered normal. What’s important is that your baby grows steadily based on her own past growth pattern. If there is ever any deviation from this, your baby’s provider will be able to help you get things back on track. Even though your little one may seem so small as a newborn, by the end of the first year you may be shocked at just how big she has become. It’s worth keeping a few mementos from your little one’s newborn period — like a hand print or footprint, or one of her first outfits — as a reminder of how far she’s come in only 12 months.

How We Wrote This Article
The information in this article is based on the expert advice found in trusted medical and government sources, such as the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists. You can find a full list of sources used for this article below. The content on this page should not replace professional medical advice. Always consult medical professionals for full diagnosis and treatment.