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How Much Should a Child Weigh? Healthy Weight by Age & Sex

How much should your child weigh? Enter age and sex to get the healthy weight range (15th–85th percentile) from official WHO growth standards, plus a full weight-by-age chart for boys and girls.

🗓️ Updated June 2026 Reviewed by Martín Rodríguez

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Reviewed by: Martín Rodríguez (editorial policy ) · Last reviewed: Jun 20, 2026

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Wondering how much your child should weigh? There is no single number—there is a healthy range that depends on age and sex. Enter your child's age and sex below and this calculator returns the healthy weight band (15th to 85th percentile) and the median (50th percentile) straight from the official WHO Child Growth Standards for ages 0–10. Below the calculator you'll find the full weight-by-age chart for boys and girls so you can read the exact numbers yourself.

When to use this calculator

You want to know if your child weighs what they should for their age.
Your pediatrician mentioned a percentile and you want to understand the range.
You want to compare your child against the official WHO weight-for-age chart.
You're worried your child looks too thin or too heavy.
You want a clear reference of expected weight at each age for boys and girls.

WHO Healthy Weight by Age — Boys and Girls (kg)

Age	Boys P15	Boys P50 (median)	Boys P85	Girls P15	Girls P50 (median)	Girls P85
Birth	2.9	3.3	3.9	2.8	3.2	3.7
6 months	6.7	7.9	9.2	6.2	7.3	8.6
1 year	8.6	9.6	10.8	7.9	8.9	10.1
2 years	10.8	12.2	13.6	10.2	11.5	13.0
3 years	12.7	14.3	16.2	12.2	13.9	15.9
4 years	14.4	16.3	18.6	14.0	16.1	18.5
5 years	16.0	18.3	21.0	15.8	18.2	21.2
6 years	17.8	20.5	23.5	17.5	20.2	23.5
7 years	19.9	22.9	26.4	19.5	22.4	26.3
8 years	22.0	25.4	29.7	21.7	25.0	29.7
9 years	24.3	28.1	33.3	24.3	28.2	33.7
10 years	26.7	31.2	37.5	27.0	31.9	38.5

Fuente: WHO Child Growth Standards (ages 0–5, 2006) and WHO Growth Reference for School-Age Children (ages 6–10, 2007). P15–P85 is the healthy range; values outside require pediatric evaluation of the full growth trajectory, not a single measurement.

How it works

There is no single 'ideal' weight for a child—there is a healthy range that shifts with age and sex. The WHO defines that range using percentiles: the 50th percentile (P50) is the median (a typical, average child), while the band between the 15th (P15) and 85th (P85) percentiles covers the great majority of healthy children. A child below P15 isn't automatically underweight, and one above P85 isn't automatically overweight—what matters is that they track their own curve consistently over time.

How It's Calculated

This calculator doesn't use a height-based formula—it reads directly from the WHO weight-for-age tables. You enter the child's age and sex, and it returns the P50 (average) and the P15–P85 healthy band for that exact age and sex. WHO standards cover 0–5 years (2006 Child Growth Standards) and the 6–10 year reference comes from the WHO 2007 school-age growth reference.

Healthy Weight by Age — Boys (kg)

Age	P15 (low)	P50 (median)	P85 (high)
Birth	2.9	3.3	3.9
6 months	6.7	7.9	9.2
1 year	8.6	9.6	10.8
2 years	10.8	12.2	13.6
3 years	12.7	14.3	16.2
4 years	14.4	16.3	18.6
5 years	16.0	18.3	21.0
6 years	17.8	20.5	23.5
7 years	19.9	22.9	26.4
8 years	22.0	25.4	29.7
9 years	24.3	28.1	33.3
10 years	26.7	31.2	37.5

Healthy Weight by Age — Girls (kg)

Age	P15 (low)	P50 (median)	P85 (high)
Birth	2.8	3.2	3.7
6 months	6.2	7.3	8.6
1 year	7.9	8.9	10.1
2 years	10.2	11.5	13.0
3 years	12.2	13.9	15.9
4 years	14.0	16.1	18.5
5 years	15.8	18.2	21.2
6 years	17.5	20.2	23.5
7 years	19.5	22.4	26.3
8 years	21.7	25.0	29.7
9 years	24.3	28.2	33.7
10 years	27.0	31.9	38.5

How to Read the Percentiles

At P50, the child weighs the same as a typical child their age—half weigh more, half weigh less.

Between P15 and P85, the weight is in the healthy range. This is where most children fall.

Below P15 or above P85, it's worth a conversation with the pediatrician—but a single reading rarely tells the whole story. A child who has always sat at P10 and grows steadily is usually fine; one who suddenly drops or jumps two percentile bands deserves a closer look.

Final Note

These figures are a reference, not a diagnosis. Genetics, nutrition, activity, sleep, and overall health all shape a child's weight. For any concern about growth, the pediatrician's longitudinal growth chart—your child's own trajectory over time—is the real measure.

Example: 5-year-old boy

Age: 5 years. Sex: boy.

Average weight (50th percentile): 18.3 kg.

Healthy range (15th–85th percentile): 16.0–21.0 kg.

A 5-year-old boy weighs an average of 18.3 kg. The healthy range is 16.0 to 21.0 kg (15th to 85th percentile). Anything inside that band is considered normal.

Disclaimer: Los resultados son orientativos y no reemplazan la consulta médica profesional. Antes de tomar decisiones con impacto, consultá con un médico, nutricionista o profesional de la salud matriculado.

Frequently asked questions

How much should a 5-year-old weigh?

Per WHO standards, a 5-year-old weighs an average of 18.3 kg (boys) or 18.2 kg (girls). The healthy range is roughly 16 to 21 kg (15th to 85th percentile).

How much should a 3-year-old weigh?

The average (50th percentile) weight for a 3-year-old is 14.3 kg for boys and 13.9 kg for girls. A healthy range is about 12.5 to 16 kg.

How much should a 1-year-old weigh?

At 12 months the average weight is 9.6 kg for boys and 8.9 kg for girls. The healthy range runs from about 7.9 to 10.8 kg depending on sex.

How do I know if my child is overweight?

If your child is above the 85th percentile on the weight-for-height or BMI-for-age chart, they're at risk of overweight; above the 97th percentile is obesity. Weight-for-age alone isn't enough—pediatricians use BMI-for-age. Talk to your doctor.

My child seems underweight—should I worry?

If they're below the 15th percentile but have always been there and are growing steadily, it's often constitutional and normal. If they've dropped across percentile bands or stopped gaining, see your doctor to rule out nutritional or health issues.

Is being below the 50th percentile bad?

No. The 50th percentile is just the median—by definition half of all healthy children weigh less than it. Sitting at the 25th or 30th percentile is perfectly normal as long as the child follows their own curve consistently.

Are WHO growth charts used worldwide?

Yes. WHO growth charts are international standards based on healthy children from six countries. They are the official reference for ages 0–5 in the US, the UK, Argentina, and most countries; the CDC charts are an alternative often used in the US for ages 2+.

Does a child's weight depend only on diet?

No. It depends on genetics (parents' build and height), nutrition, physical activity, overall health, and sleep. An active, well-fed child usually settles into a healthy weight on their own.

How often should I weigh my child?

At regular pediatric checkups: roughly monthly in the first year, every 3–6 months until age 3, then annually. Frequent weighing at home isn't necessary and can cause needless worry.

Why does growth sometimes look uneven?

Growth isn't linear. There are rapid-growth spurts where a child can look thin, and periods of more weight gain just before a height spurt. The dip and rebound around ages 5–6 (called the adiposity rebound) is normal.

Sources & references

Methodology & trust

Editorial

Calculadora de salud revisada por el equipo editorial de Hacé Cuentas, contrastada con WHO — Child Growth Standards (weight-for-age), según nuestra política editorial y metodología.

Updates

Última revisión: June 20, 2026. Los parámetros se verifican periódicamente con las fuentes citadas.

Privacy

Calculations run 100% in your browser. We do not store or transmit your data.

Limitations

Indicative results. For critical decisions, consult a professional.

📌 How to cite this calculator

Rodríguez, M. (2026). How Much Should a Child Weigh? Healthy Weight by Age & Sex. Hacé Cuentas. https://hacecuentas.com/peso-ideal-ninos

Contenido bajo licencia CC-BY 4.0 — reutilizable citando la fuente con enlace a Hacé Cuentas.

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