Ideal Weight for Children by Age and Height — What Parents Need to Know

Assessing a child's weight is more complex than for adults. You can't just use BMI categories directly, and a number on a scale tells you nothing without knowing the child's age and height. A child who weighs 35 kg might be perfectly healthy at age 12 and overweight at age 8.

This article covers how children's healthy weight is actually assessed, what the reference ranges look like by age, and how to interpret growth chart results. For adult ideal weight calculations, the Ideal Weight Calculator uses the standard clinical formulas.

How Children's Weight Is Assessed: Growth Charts, Not Fixed Numbers

For adults, there are fixed BMI thresholds (18.5 for underweight, 25 for overweight, 30 for obese). For children, these thresholds don't apply. Instead, children's weight is assessed using BMI-for-age percentiles, which compare a child's BMI to other children of the same age and sex.

A child's BMI percentile tells you where they fall in the population distribution:

So a child with a BMI at the 70th percentile is healthy — this means 70% of children their age and sex have a lower BMI, and 30% have a higher one. The 70th percentile is firmly in the healthy range.

The key difference from adults: the same BMI of 20 means something different for a 6-year-old, a 10-year-old, and a 14-year-old. In a 10-year-old, BMI 20 is around the 90th percentile — overweight. In a 14-year-old, BMI 20 is around the 50th percentile — solidly normal.

Average Weight and Height Ranges by Age

The following values represent the 50th percentile (median) for US children. About half of healthy children at each age will weigh more than this, and half will weigh less.

Boys

Girls

These are median values. A healthy 10-year-old boy might weigh anywhere from 25 to 45 kg depending on height and body composition.

Why BMI Changes So Much During Childhood

Children's BMI follows a distinctive pattern that's different from what many parents expect. BMI actually decreases from age 1 through about age 5–6 in most children (this is called "adiposity rebound"), then rises again through adolescence.

This means:

• A 5-year-old and a 10-year-old have different healthy BMI ranges, with the 5-year-old typically having a lower healthy BMI
• Comparing a child's BMI to an adult scale or to their older sibling's old BMI numbers is meaningless
• Some weight gain is expected and normal throughout childhood; concern arises when the growth curve shows consistent upward trajectory across percentile lines

The consistent upward trend matters more than any single measurement. A child who gains two percentile categories over 6 months warrants closer attention; a child who stays at the 85th percentile consistently is a different situation from one who was at the 60th and climbed to the 85th.

How to Read Your Child's Growth Chart

Your pediatrician will plot your child's weight, height, and BMI on age-specific growth charts (typically the CDC growth charts for the US, or WHO charts for younger children). Here's how to interpret what you see:

The shape of the curve matters. A child tracking along the 75th percentile consistently is growing normally. A child who was at the 50th and is now trending toward the 85th or 90th may need evaluation, even if the current percentile isn't alarming yet.

Height and weight should track together. A child who is tall for their age will often be heavier, and that's appropriate. A child at the 90th percentile for height and 60th percentile for weight is thin; the same weight at the 30th percentile for height would be overweight.

Short-term fluctuations are normal. Growth doesn't happen in a straight line. Children gain weight in bursts, often before growth spurts in height. A weight measurement that looks high may look completely proportional once height catches up in the next 3–6 months.

When to Talk to a Pediatrician

Growth charts are screening tools, not diagnoses. Bring concerns to your child's doctor if:

• Your child's BMI percentile is above the 95th for their age and sex
• You notice your child's curve has been trending upward across multiple percentile lines over 6–12 months
• Your child has a BMI below the 5th percentile, or has been losing weight unexpectedly
• You notice signs of eating concerns: restricting food, secretive eating, significant body dissatisfaction

The pediatrician will look at the full picture — growth history, family history, physical activity, diet, and development — rather than a single number.

What Adult Ideal Weight Formulas Apply To

The Hamwi, Devine, Robinson, and Miller formulas used in adult ideal weight calculators were designed for adults 18 and older. They aren't applicable to children. If you're looking for an adult reference, the Ideal Weight Calculator calculates the average across these formulas for adult heights.

For children in their late teens (17–18), adult formulas begin to become applicable as growth nears completion, but the standard pediatric growth chart approach remains the better tool until adulthood is fully reached.

Supporting Healthy Weight in Children

The goal for children in a healthy weight range is to support continued healthy growth — not to maintain a specific number. For children who are overweight or obese, the standard recommendation from pediatric organizations is often weight maintenance rather than weight loss while the child grows into their weight over time, unless the excess weight is causing immediate health complications.

Practically, this means:

• Regular physical activity (at least 60 minutes of moderate activity per day for children)
• Reducing sedentary screen time
• Family meals and a varied diet without restricting entire food groups
• Avoiding diet culture messaging that makes children feel bad about their body

Children are not small adults when it comes to weight and nutrition. The approach that applies to adult weight management — calorie counting, specific weight loss targets — is generally not appropriate for children and can cause harm if applied incorrectly.