乳幼児発育曲線・成長パーセンタイル計算機（0〜5歳） - 無料オンライン計算ツール

WHO成長基準に基づき、0〜5歳の乳幼児の身長・体重パーセンタイルを判定。健やかな発育を見守るツール。

よく検索されるキーワード：What percentile is my 2-year-old in weight?WHO weight for age percentiles calculation How to calculate child growth z-score

What is a percentile, and why do parents check it? A percentile shows where your child stands among 100 children of the same age and sex. At the 25th percentile, about 25 kids weigh less and about 75 weigh more. Doctors track weight and length over several visits to see whether a child is growing along their own curve.

Educational child growth reference based on WHO Child Growth Standards (2006). Any diagnosis or clinical treatment belongs to your pediatrician.

What is a percentile, and why do parents check it?

A percentile shows where your child stands among 100 children of the same age and sex. At the 25th percentile, about 25 kids weigh less and about 75 weigh more. Doctors track weight and length over several visits to see whether a child is growing along their own curve.

The key point: a percentile is not a score or a grade. The 50th is not 'good' and the 10th is not 'bad'. The 50th is simply the middle (the median). This page gives you a rough comparison with the WHO median. Any diagnosis or treatment decision belongs to your pediatrician.

How to Use This Calculator

What to enter

1Gender

Select boy or girl.

2Age

Slide in months (0 to 60 months).

3Weight

Enter current weight in kg.

4Height / length

Enter height/length in cm.

Outputs:You will see: an approximate weight percentile, an approximate height percentile, the WHO median weight and height, and a 'Your child vs WHO 50th' visual comparison chart.

Height or length?

Children under 2 years (24 months) are measured lying down (recumbent length), and after that standing up (standing height). Standing height is about 0.7 cm less than lying length, so use the same measurement method your doctor used.

About the chart

Height is shown divided by 5 (cm ÷ 5) on the visual bar chart so weight and height fit comfortably on a single scale. This is purely a display choice.

Practical Proof

Worked Calculation Examples (Based on Widget Logic)

Widget logic: Divides child's weight/height by its approximate median formula and assigns a percentile bin based on the ratio.

Weight Ratio RulesWeight ratio: >1.2 → ~90th | >1.1 → ~75th | >0.95 → ~50th | >0.85 → ~25th | otherwise → ~10th

Height Ratio RulesHeight ratio: >1.05 → ~85th | >1.02 → ~65th | >0.98 → ~50th | >0.94 → ~25th | otherwise → ~10th

Example 1: Boy, 24 months, 12.2 kg, 87.5 cm (Widget Default)

Widget median: Weight 12.2 kg, Height 87.7 cm

Ratios: Weight 12.2 ÷ 12.2 = 1.00 → ~50th | Height 87.5 ÷ 87.7 = 0.998 → ~50th

Meaning: Both measurements are very close to the WHO median.

Example 2: Girl, 36 months, 13.0 kg, 93 cm

Widget median: Weight 13.7 kg, Height 94.1 cm

Ratios: Weight 13.0 ÷ 13.7 = 0.95 → ~25th | Height 93 ÷ 94.1 = 0.99 → ~50th

Meaning: Weight is a little below the median, height is near it. A single measurement says little; doctors look at the growth trend over several visits.

Example 3: Why does the result show '~'?

The percentile comes in rounded step bins (10/25/50/75/90), hence the '~'. A child at the 4th percentile and one at the 20th can both show '~10th'. For finer clinical detail, refer to your pediatrician's official plotted WHO growth curve.

Reference Tables

Official WHO 2006 reference medians and calculator formula comparisons:

Table A - WHO 2006 Median (50th Percentile) Approximate Values

Age	Boy Weight	Girl Weight	Boy Length/Height	Girl Length/Height
Birth	3.3 kg	3.2 kg	49.9 cm	49.1 cm
6 Mos	7.9 kg	7.3 kg	67.6 cm	65.7 cm
12 Mos	9.6 kg	8.9 kg	75.7 cm	74.0 cm
18 Mos	10.9 kg	10.2 kg	82.3 cm	80.7 cm
24 Mos	12.2 kg	11.5 kg	87.1 cm (height) / 87.8 cm (length)	85.7 cm (height) / 86.4 cm (length)
36 Mos	14.3 kg	13.9 kg	96.1 cm	95.1 cm
48 Mos	16.3 kg	16.0 kg	103.3 cm	102.7 cm
60 Mos	18.3 kg	18.2 kg	110.0 cm	109.4 cm

Note: Recumbent length is measured up to 24 months, standing height thereafter (~0.7 cm difference). These are approximate WHO reference medians.

Table B - How This Widget Estimates Median (Linear Formulas)

Age	Boy Weight	Girl Weight	Boy Height	Girl Height
12 Mos	9.6 kg	8.9 kg	75.7 cm	74.0 cm
24 Mos	12.2 kg	11.5 kg	87.7 cm (length) / 87.1 cm (height)	86.4 cm (length) / 85.7 cm (height)
36 Mos	14.2 kg	13.7 kg	95.1 cm	94.1 cm
48 Mos	16.3 kg	16.0 kg	102.6 cm	101.8 cm
60 Mos	18.3 kg	18.2 kg	110.0 cm	109.4 cm

Note: For infants 0 to 12 months, the widget uses the official WHO 2006 monthly median lookup table, and closely tracks WHO reference medians from 12 to 60 months. Values across 0 to 60 months directly align with official WHO reference medians.

Table C - Common Percentile Ranges & What They Mean

Percentile	Everyday Plain-Language Meaning
Below 3rd	Warrants pediatrician evaluation (fewer than 3 in 100 children are lighter/shorter)
3rd – 15th	Below average, but frequently within healthy individual genetic variation
15th – 85th	Broad typical middle range where the majority of healthy children grow
85th – 97th	Above average, but frequently within healthy individual genetic variation
Above 97th	Warrants pediatrician evaluation (fewer than 3 in 100 children are heavier/taller)

Note: Clinical boundaries are evaluated individually by pediatricians. This tool groups into bins and does not distinguish <3rd or >97th outliers (lowest step is ~10th, highest is ~90th).

Table D - Quick Clarifications on Common Growth Questions

Common Question / Myth	Accurate Medical Fact
Is 50th percentile the 'ideal' weight?	No, it is simply the middle number (median), not a goal or grade.
Is 10th percentile 'too low'?	Not by itself. Steady growth along a child's own percentile line is what matters.
Why is length different from height?	Length is measured lying down (<24 mo); standing height is ~0.7 cm shorter.
Do WHO charts apply internationally?	Yes, WHO standards reflect optimal growth worldwide across diverse ethnicities.

How accurate is this calculator, and why trust the WHO charts at all?

The WHO Child Growth Standards (2006) are based on the Multicentre Growth Reference Study (MGRS) of healthy, breastfed children raised in optimal conditions across six diverse countries. That is why they are called a 'standard': an international reference for how children can grow under healthy nutrition and healthcare.

This online tool, however, is not the full clinical WHO LMS chart. The full clinical WHO percentile is calculated using Box-Cox power exponential LMS parameters (L, M, S) for each specific age to derive an exact continuous z-score. This calculator instead estimates the median using simplified piecewise linear formulas, then bins your child into approximate percentile steps.

Three practical consequences follow from this implementation:

•The result is an approximation, which is why '~' appears in front of all percentile figures.
•For infants 0 to 12 months, the calculator directly references official WHO 2006 monthly median tables, and for older children it closely follows WHO growth curves.
•The lowest step is ~10th and the highest is ~90th, so this tool does not flag extreme outliers below the 3rd or above the 97th percentile. For clinical evaluations, refer to your pediatrician's plotted chart.

One more fundamental clinical principle: a single measurement decides nothing. What matters is the longitudinal trend over multiple pediatric checkups. A child who has tracked the 10th percentile curve since infancy and is active and developing well is usually healthy. Conversely, a sudden drop across two or more major percentile lines or stagnant weight gain warrants professional medical review.

Premature infants (born before 37 weeks) require corrected age adjustments and specialized preterm growth charts (such as Fenton growth curves). This online calculator does not support corrected age adjustments; parents of premature infants should always rely directly on their pediatrician's guidance.

When to See a Pediatrician (Safety & Clinical Flags)

Consult your pediatrician or healthcare provider promptly if:

Your pediatrician's plotted clinical measurement falls below the 3rd or above the 97th percentile.
Your child's growth curve suddenly drops across two or more major percentile curves.
Weight gain has completely stalled or your child has lost weight over several consecutive weeks.
Your child eats very little, appears unusually lethargic or weak, or falls ill frequently.
You feel concerned for any reason. A parent's intuition is always a valid reason to consult a doctor.

⚠️ Please never start unprescribed weight-gain supplements, tonics, or restrictive diets without qualified medical supervision.

Explore Connected Family & Health Calculators

Explore Connected Pediatric & Family Health Calculators

Need to determine your child's exact chronological age in months and days for precise WHO percentile tracking? Use our Age Calculator. Expecting parents or families planning for a new arrival can estimate milestone delivery timelines and gestational weeks using our clinical Pregnancy Due Date Calculator. To monitor recommended maternal nutrition and trimester-by-trimester weight progress, consult our Pregnancy Weight Gain Calculator. For children graduating past 5 years (60 months) and for parent wellness tracking, continue with our comprehensive BMI Calculator to monitor body mass index trends over time.

よくある質問（FAQ）

Frequently Asked Questions (FAQ)

Is the 50th percentile the ideal weight?

No. It is only the middle value (the median). Children growing anywhere between roughly the 3rd and 97th percentiles are typically within healthy ranges. Steady growth along their own curve matters far more than matching the 50th percentile.

Is the 10th percentile bad for a toddler?

Not by itself. If your toddler has followed the 10th percentile line steadily since birth, has good energy, and meets milestones, it is often completely normal. If their curve suddenly drops, consult your pediatrician.

How much should a 2-year-old weigh?

According to WHO medians at 24 months, a boy weighs approximately 12.2 kg (26.9 lbs) and a girl weighs approximately 11.5 kg (25.4 lbs). Normal variation above and below this median is expected.

How much should a 6-month-old weigh?

The official WHO median at 6 months is about 7.9 kg for boys and 7.3 kg for girls. This calculator references the official WHO 2006 monthly medians to accurately reflect these values.

My child's weight is low. What should I do?

First check whether your child is steadily gaining weight along their own growth line. If you have concerns, schedule a visit with your pediatrician. Do not give over-the-counter supplements without medical advice.

Does breastfed vs formula-fed matter for WHO charts?

The WHO standards were built using healthy breastfed children as the biological norm, but the standards are designed to monitor growth for all children regardless of feeding method.

How accurate is this calculator?

It provides a rapid, educational estimate. It differs from the true continuous WHO LMS tables, particularly for infants under 12 months. It does not replace clinical measurements taken by a pediatrician.

Can I show this result to my doctor?

You can mention it as a conversation starter, but your pediatrician will plot measurements on their official calibrated charts and conduct a comprehensive physical exam.