What Is A Baby's Average Weight By Month?
Babies come in different shapes and sizes and grow at their own pace. However, growth charts can indicate the average weight a baby should reach at various stages of their development. Weight is one way to measure a baby's physical growth.
It is important to remember that average weight is not necessarily "normal" weight for babies. Babies come in all shapes and sizes, and a baby's weight in the lower percentile does not necessarily mean a problem with their development. Using a weight chart can be a helpful tool for tracking a baby's growth and development.
It is essential to consult a doctor if the baby's weight drops or stays in the 10th or 9th percentile for two or more weeks. Babies in the 10th or 9th percentile for two or more weeks may be underweight and need additional nutrition or monitoring.
This article looks at the typical weight of a newborn as it grows month to month, as well as what can cause variations in a baby’s weight.
Average Newborn Weight (WHO Guidelines)
The World Health Organisation (WHO) states that the typical birth weight of a full-term male baby is 7 pounds 6 ounces (3.3 kilograms). The average birth weight of full-term females is 7 pounds 2 ounces (3.2 kilograms).
Babies between 37 and 40 weeks of gestation typically weigh 2.5 to 4 kilograms, equivalent to 5 pounds 8 ounces and 8 pounds 13 ounces, respectively.
According to medical professionals, an infant's weight is considered low at birth if it is less than 5 pounds and 8 ounces (2.5 kilograms).
Newborns often experience a weight loss of around 10% shortly after birth, which is attributed to fluid loss and is typically not a cause for concern. This weight is generally regained within seven days.
Baby Weight Chart by Month (Boys vs Girls)
This information can be used to determine the baby's overall health. If a baby is underweight, it may indicate that they are not getting the right amount of nutrients. If a baby is overweight, it may indicate they are eating too many calories.
This indicates that a baby's weight may not be considered too much or too little, but rather within a range on a spectrum.
The chart below shows the average weight of babies at the 50th percentile. Generally, male babies weigh slightly more than female babies, so the data is divided by gender.
Average Baby Weight by Month (50th Percentile)
| Age | Girls (kg/lb) | Boys (kg/lb) |
|---|---|---|
| Birth | 3.2 kg / 7 lb 2 oz | 3.3 kg / 7 lb 6 oz |
| 1 month | 4.2 kg / 9 lb 4 oz | 4.5 kg / 9 lb 14 oz |
| 3 months | 5.8 kg / 12 lb 14 oz | 6.4 kg / 14 lb 1 oz |
| 6 months | 7.3 kg / 16 lb 1 oz | 7.9 kg / 17 lb 8 oz |
| 9 months | 8.2 kg / 18 lb 2 oz | 8.9 kg / 19 lb 10 oz |
| 12 months | 8.9 kg / 19 lb 12 oz | 9.6 kg / 21 lb 4 oz |
Baby Growth Patterns: What Parents Can Expect
During the initial 6 months of a baby's life, they tend to grow and gain weight at a rapid rate. Depending on the baby, this can range from 4 to 7 ounces or 113 to 200 grams (g) weekly.
Weight gain slows slightly, with an average increase of around 3–5 oz (about 85–140 g) per month from 6 to 18 months. On average, babies have tripled their birth weight by the time they reach their first birthday.
Growth patterns need to follow a precise schedule, however.
Some babies gain a steady weight and remain in the same percentile for long periods. Others gain weight rapidly, signalling an increase in weight that can happen over time. This may result in a baby moving into a new weight category.
Factors That Influence Baby Weight and Growth
Rather than relying solely on weight, parents should also pay attention to other indicators of physical development in their baby, such as length and head circumference.
Considering a baby's weight, length, and head circumference enables doctors to compare their growth with that of other infants of the same age and gender.
It is crucial to have an understanding of a child's developmental milestones.
Several factors can affect the weight of a baby, such as
Sex
Male babies tend to have a higher birth weight than female babies and usually gain weight more quickly during the early stages of development.
Nutrition
A baby's weight and growth progress can be affected by whether they are breastfed or fed formula.
Breastfed infants gain more weight than formula-fed babies during the first six months.
Medical Conditions
Underlying health conditions, such as congenital heart defects, can affect infants' weight gain rates. Babies with such requirements may experience slower weight gain than those without this condition.
Conditions that interfere with the absorption or digestion of nutrients, like celiac disease, can cause a person to lose weight slowly.
Prematurity
Infants born before their due date often develop more slowly in terms of size and weight initially. However, they tend to be on the same growth trajectory as full-term babies by their first birthday.
Summary
The typical weight of male babies born at full-term is 7 lb 6 oz, or 3.3 kg. Conversely, the typical birth weight for female babies born at full-term is 7 lb 2 oz, or 3.2 kilograms.
Healthcare professionals use baby weight charts to compare a baby's weight to the average weight of babies of the same age and sex, tracking the baby's physical development.
A doctor typically evaluates a baby's physical development based on consistent growth rather than a specific percentile. Furthermore, a baby's weight percentile does not determine their size as an adult, just as a baby's length does not determine their height as an adult.
While tracking the average weight of babies by month can help monitor their physical development, doctors also consider other key factors, such as length and head circumference, to assess their overall growth and development.
Healthcare practitioners consider whether a baby is achieving other developmental milestones in a timely manner. They also conduct a thorough medical history to rule out potential medical or nutritional issues that could impact a baby's weight gain.
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