Compare your baby's weight and length (0-24 months) against approximate WHO growth medians for their age and gender. A rough estimate, not a clinical percentile.
Enter Your Baby's Details
Enter gender, age, weight, and height to compare against growth medians
This baby weight and height calculator gives parents and caregivers a quick, informal comparison of a baby's current weight and length against approximate WHO (World Health Organization) growth reference medians for babies of the same age (0–24 months) and gender. It's designed as a rough, general-purpose check between well-child visits — a starting point for curiosity, not a replacement for the growth chart and percentile tracking your pediatrician performs at every appointment.
The calculator holds a small built-in table of approximate WHO median weight and height values at 13 common reference ages (0, 1, 2, 3, 4, 5, 6, 9, 12, 15, 18, 21, and 24 months), stored separately for boys and girls. When you enter your baby's exact age, weight, and height, it linearly interpolates between the two nearest reference ages to estimate a median value for that exact age, then expresses your baby's entered weight and height as a percentage of that interpolated median. The result is a rough classification band, not a calibrated percentile score.
This tool is meant for parents, grandparents, and caregivers of babies from birth to 24 months who want a quick, informal sense of how their baby's current weight and length compare to typical growth patterns. It can be useful while preparing for a pediatrician visit or simply satisfying curiosity after a home measurement. It is not designed to replace clinical growth monitoring, and it does not adjust for prematurity, so parents of premature infants should rely on their pediatrician's corrected-age tracking instead.
A quick comparison against typical growth patterns can help you notice if something seems significantly off track between checkups, which can prompt a timely, well-informed conversation with your pediatrician. That said, a single measurement compared against a median is far less informative than tracking a baby's own growth curve over multiple visits — which is exactly what an actual percentile-based growth chart captures. Babies grow in spurts and plateaus, and healthy babies can sit anywhere along a normal growth curve, so context and trend matter more than any one reading.
The exact interpolation and classification logic this calculator runs in your browser
Where age₁ and age₂ are the two nearest stored reference ages (in months) that bracket the age you entered, Median(age₁) and Median(age₂) are the built-in WHO-based median weight or height values at those ages for your baby's gender, and Age is the exact age you entered. Weight and height are each interpolated and classified independently, using their own reference table.
Median weight and height values are stored at 0, 1, 2, 3, 4, 5, 6, 9, 12, 15, 18, 21, and 24 months, separately for boys and girls, based on approximate WHO growth standards.
Growth between reference points isn't perfectly linear in reality, but linear interpolation between nearby ages gives a reasonable, simple estimate for any age you enter, without needing a full growth-curve model.
Under 85% of median: Well Below Average | 85–95%: Below Average | 95–105%: Average | 105–115%: Above Average | Over 115%: Well Above Average.
From entering your baby's details to reading the growth comparison
Choose Boy or Girl so the calculator compares your baby's weight and height to the correct WHO-based reference values for that gender.
Type your baby's current age, from 0 to 24 months in half-month increments, into the age field.
Select Metric (kg/cm) or Imperial (lb/in) depending on which units you have your baby's measurements in.
Type your baby's most recent weight and length/height measurements into the corresponding fields for your chosen units.
The calculator interpolates an age-matched median from its reference table and shows your baby's weight and height classification, the median values, percent-of-median figures, and comparison charts.
Using the calculator's own default scenario — a boy, age 6 months, 7.9 kg and 67.6 cm
Suppose your baby is a boy, 6 months old, weighing 7.9 kg and measuring 67.6 cm long.
Explanation: In this example the default weight and height inputs happen to exactly match the boy reference table's values at 6 months, so both come out at precisely 100% of median — landing in the "Average" band. In practice, most entered measurements won't fall exactly on a stored reference age and will typically land somewhere between two reference points, requiring the interpolation fraction to take a value between 0 and 1 rather than exactly 1.0 as shown here. Either way, this is a single-point comparison — it is not a substitute for the percentile your pediatrician would calculate from a full growth chart.
What each classification band generally suggests
| % of Median | Classification | What This Comparison Suggests |
|---|---|---|
| Under 85% | Well Below Average | Noticeably below the interpolated reference median — worth mentioning at your next pediatrician visit, especially if this is a consistent pattern |
| 85% – 95% | Below Average | Somewhat below the reference median; many healthy babies fall in this range |
| 95% – 105% | Average | Close to the interpolated reference median for age and gender |
| 105% – 115% | Above Average | Somewhat above the reference median; many healthy babies fall in this range |
| Over 115% | Well Above Average | Noticeably above the interpolated reference median — worth mentioning at your next pediatrician visit, especially if this is a consistent pattern |
If your baby's result falls in the Average band: this simply means your baby's current weight or height is close to the interpolated reference median for their age and gender — it is not a guarantee of health, just a proximity comparison.
If your baby's result falls in a Below/Above Average or Well Below/Well Above Average band: this is not, by itself, a health concern. A single below-average or above-average reading is far less informative than a consistent trend tracked over multiple visits — babies grow in spurts and plateaus, and healthy babies can sit anywhere along a normal growth curve. Pediatricians track growth using official WHO/CDC growth charts across many visits, not a single comparison like this one.
This result is for informational purposes only and is not a medical diagnosis. This tool cannot tell you whether your baby's growth pattern is healthy — only your pediatrician, using your baby's full growth history, can make that assessment.
This calculator provides educational estimates only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Results may vary depending on individual health conditions. Always consult a qualified healthcare professional regarding medical concerns.
Where a quick, informal growth comparison is genuinely useful
Get a rough sense of your baby's growth before a well-child visit so you can ask informed questions.
Satisfy curiosity after a home weigh-in without needing to call the pediatrician's office.
Recalculate every few weeks to see whether your baby's growth is trending in a consistent direction.
See how growth compares to the reference median after introducing solid foods.
Understand how WHO gender-specific medians differ at the same age.
Switch between metric and imperial units — useful for international parents, expats, or travelers.
Give grandparents or family members a quick, informal reference point to understand typical growth patterns.
Illustrate how age-matched growth medians and interpolation work in a classroom or training setting.
Provide a non-clinical talking point when discussing a child's development with caregivers.
Turn a vague "is this normal?" worry into specific, concrete numbers to discuss with your doctor.
What this baby growth calculator does well, and where it can't replace professional pediatric care
The exact reference values this calculator interpolates between
| Age (months) | Boy Median Weight | Girl Median Weight | Boy Median Height | Girl Median Height |
|---|---|---|---|---|
| 0 | 3.3 kg | 3.2 kg | 49.9 cm | 49.1 cm |
| 1 | 4.5 kg | 4.2 kg | 54.7 cm | 53.7 cm |
| 2 | 5.6 kg | 5.1 kg | 58.4 cm | 57.1 cm |
| 3 | 6.4 kg | 5.8 kg | 61.4 cm | 59.8 cm |
| 4 | 7.0 kg | 6.4 kg | 63.9 cm | 62.1 cm |
| 5 | 7.5 kg | 6.9 kg | 65.9 cm | 64.0 cm |
| 6 | 7.9 kg | 7.3 kg | 67.6 cm | 65.7 cm |
| 9 | 8.9 kg | 8.2 kg | 72.0 cm | 70.1 cm |
| 12 | 9.6 kg | 8.9 kg | 75.7 cm | 74.0 cm |
| 15 | 10.3 kg | 9.6 kg | 79.1 cm | 77.5 cm |
| 18 | 10.9 kg | 10.2 kg | 82.3 cm | 80.7 cm |
| 21 | 11.5 kg | 10.9 kg | 85.1 cm | 83.7 cm |
| 24 | 12.2 kg | 11.5 kg | 87.8 cm | 86.4 cm |
Summary: This baby weight and height calculator gives you a free, instant comparison of your baby's weight and length to approximate WHO-based growth medians for their age and gender — a useful, informal starting point, not a medical diagnosis or official percentile. Pair it with related tools like the Pregnancy Due Date Calculator and BMI Calculator for a fuller picture across pregnancy, infancy, and beyond.
Common questions about baby growth estimates
Official guidance to complement this calculator — not a substitute for licensed pediatric medical advice
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