Weight is one indicator of a baby’s physical development. Children develop at different paces, but growth charts can provide a guide to how much a baby should weigh, on average.
First, it is worth noting that average weight is not “normal” weight. Just like adults, babies come in all shapes and sizes. If a baby’s weight is in a lower percentile, this does not necessarily signal a problem with their growth or physical development. With this in mind, using a weight chart can help a person generally track their baby’s growth.
This article describes the average weight of a baby month by month from birth. It also explores what can affect a baby’s weight.
The average weight of a baby born at 37–40 weeks ranges from 5 lb 8 oz to 8 lb 13 oz. This is 2.5 to 4 kg.
It is common for babies to lose around 10% of their weight shortly after birth. This decrease is mostly due to fluid loss and usually nothing to worry about. Most babies gain back this weight within 1 week.
Weight charts can help a person tell what percentile their baby’s weight falls into. For example, if their weight is in the 60th percentile, it means that 40% of babies of the same age and sex weigh more, and 60% of these babies weigh less.
This does not necessarily mean that any baby weighs too much or too little. It can simply indicate where a baby’s weight falls on a spectrum.
The chart below shows baby weights in the 50th percentile. This is the average weight. Male babies tend to weigh a little more than female babies, so the chart is divided by sex.
|Birth||7 lb 2 oz (3.2 kg)||7 lb 6 oz (3.3 kg)|
|1 month||9 lb 4 oz (4.2 kg)||9 lb 14 oz (4.5 kg)|
|2 months||11 lb 5 oz (5.1 kg)||12 lb 4 oz (5.6 kg)|
|3 months||12 lb 14 oz (5.8 kg)||14 lb 1 oz (6.4 kg)|
|4 months||14 lb 3 oz (6.4 kg)||15 lb 7 oz (7.0 kg)|
|5 months||15 lb 3 oz (6.9 kg)||16 lb 9 oz (7.5 kg)|
|6 months||16 lb 1 oz (7.3 kg)||17 lb 8 oz (7.9 kg)|
|7 months||16 lb 14 oz (7.6 kg)||18 lb 5 oz (8.3 kg)|
|8 months||17 lb 8 oz (7.9 kg)||18 lb 15 oz (8.6 kg)|
|9 months||18 lb 2 oz (8.2 kg)||19 lb 10 oz (8.9 kg)|
|10 months||18 lb 11 oz (8.5 kg)||20 lb 3 oz (9.2 kg)|
|11 months||19 lb 4 oz (8.7 kg)||20 lb 12 oz (9.4 kg)|
|12 months||19 lb 12 oz (8.9 kg)||21 lb 4 oz (9.6 kg)|
Babies grow and gain weight the fastest within the first 6 months of life. Although this can vary, babies tend to gain around 4–7 oz, or 113–200 grams (g), per week in the first 4–6 months.
Weight gain then slows slightly, with an average gain of around 3–5 oz (about 85–140 g) per week when the baby is 6–18 months. On average, babies triple their birth weight by their first birthday.
Growth patterns do not follow a clear schedule, however.
Some babies gain weight steadily and stay in the same percentile, or close to it, for several months. Others gain weight rapidly, signalling a growth spurt, which can happen at any time. This may move a baby into a new weight percentile.
It is important not to focus on weight as the only indicator of physical development. Other measurements of this development include the baby’s length and head circumference.
Considering all three measurements gives doctors an idea about how the baby is growing, compared with other babies of the same age and sex.
Meanwhile, it is also important to keep other developmental milestones in mind. Various checklists of milestones by age are available, including one from Pathways.org, which is endorsed by organizations such as the American Academy of Pediatrics and the National Association of Pediatric Nurse Practitioners.
For anyone looking for more information about what influences the weight of a baby, several factors can be involved, including:
Male newborns tend to be bigger than female newborns, and they typically gain weight a little faster during infancy.
Weight gain and growth rates can also depend on whether the baby consumes breast milk or formula.
The American Academy of Pediatrics notes that breastfed babies gain weight and grow faster than formula-fed babies during the first 6 months.
However, that rate can shift during the next 6 months. Breastfed babies may gain weight and grow more slowly than formula-fed babies when they are aged 6 months to 1 year.
Health issues that affect nutrient absorption or digestion, such as celiac disease, may also lead to slow weight gain.
Babies born prematurely may grow and gain weight more slowly during their first year than babies born at full term.
However, many babies born prematurely gain weight rapidly and “catch up” by about their first birthday.
The average birth weight for full-term male babies is
Baby weight charts can help a healthcare team track a baby’s physical development by comparing the baby’s weight with the weights of others of the same age and sex.
Still, a doctor usually looks for steady growth, rather than a target percentile, when assessing a baby’s physical development. And even if a baby’s weight is in a lower percentile, they will not necessarily be a small adult — just as longer babies do not necessarily become tall adults.
Knowing about average weights by month can help people gauge their babies’ physical development, but doctors also look for other important indicators, such as length and head circumference.
Healthcare professionals also take into account whether a baby is generally hitting other milestones on time. And by taking a detailed medical history, they can rule out any medical conditions or nutritional considerations that may be preventing a baby from gaining weight appropriately.