Baby Height Percentile Calculator

The baby height percentile calculator compares your baby's length with the WHO standards for the same sex and age (birth to 24 months). Enter age and length lying down in centimeters or inches to get the percentile, z-score, median length and the usual 3rd to 97th percentile range.

How to use the Baby Height Percentile Calculator

1. Select your baby's sex.
2. Enter age in months and extra days (adjusted age if born early).
3. Enter length measured lying down and choose centimeters or inches.
4. Press Calculate to see the percentile, z-score and the median length for age.

Formula and method

The WHO publishes three numbers for each sex at each age: L (skewness), M (median) and S (coefficient of variation). The calculator interpolates them to your baby's exact age in months and days and computes z = ((measurement / M)^L − 1) / (L × S), or ln(measurement / M) / S when L is 0. The percentile is the normal distribution function of z times 100. A z-score of 0 is the 50th percentile, −2 is about the 2nd and +2 is about the 98th.

The WHO tables used here are the monthly LMS values from birth to 24 months. Between whole months the calculator interpolates linearly, so results can differ from the WHO daily tables by a small fraction of a percentile point.

Baby length by age (WHO)

How fast do babies grow in length?

Typical monthly growth in length (change in the WHO median from month to month) is fastest in the first months and slows after the first birthday.

Length versus height

Children under 2 are measured lying down on a measuring board and the number is called length. From age 2 children are measured standing and the number is called height. Standing height is about 0.7 cm less than lying length at the same age, so the CDC and WHO use separate charts. This page uses the WHO length-for-age chart. After age 2 use the Height Percentile Calculator.

What is a normal length percentile?

Any percentile from the 3rd to the 97th is within the usual range. Tall parents tend to have longer babies, and babies born small can catch up in the first year, so it is normal for a baby to move percentile lines during the first 6 to 12 months.

Length, genetics and catch-up growth

Birth length reflects the mother's size and the pregnancy, while later length depends more on genes. That is why babies often shift toward the percentile their parents would predict. Babies born prematurely often catch up between the first and second year.

Premature babies and adjusted age

Babies born before 37 weeks are usually plotted by adjusted (corrected) age until about 24 months. Adjusted age is the age since birth minus the number of weeks early. Enter the adjusted age in the age boxes and ask your baby's doctor how they interpret the result, because very preterm babies often follow their own curves. The Adjusted Age Calculator works out the adjusted age for you.

How to measure a baby's length accurately

Lay the baby on a flat surface, with a helper holding the head against a fixed headboard and the legs gently straightened. Mark the heel with a flat board at a right angle. Measure to the nearest 0.1 cm or 1/8 inch. A cloth tape on a squirming baby can be 1 to 2 cm off, so compare clinic readings over time.

Low and high length percentiles

A baby below the 3rd or above the 97th percentile, or one who moves two major lines down, should be reviewed by a doctor. Causes range from normal family size to feeding problems or medical conditions, so a clinician should look at the full picture.

When to call the doctor

Call your baby's doctor or nurse if a measurement is below the 3rd or above the 97th percentile, if a percentile has crossed two major lines (for example from the 50th to the 10th), if your baby is not regaining birth weight by about two weeks, is feeding poorly, has fewer wet diapers than usual, seems unusually sleepy or fussy, or if you are worried for any reason. Do not wait for the next routine visit if something seems wrong.

Frequently asked questions

How long is a newborn baby?

The WHO median at birth is 49.9 cm (19.6 in) for boys and 49.1 cm (19.3 in) for girls.

How tall will my baby be as an adult?

There is no reliable prediction from a baby's length percentile alone. After age 2, the Height Percentile Calculator includes a parent-based estimate.

What if my baby is in the 90th percentile for length?

That is common and healthy. Long babies often have tall parents. Doctors check weight-for-length and growth over time.

Why is my baby's length percentile different from weight percentile?

Length and weight are independent measures. Different percentiles for each are normal; weight-for-length shows if they are in proportion.

Can I measure my baby's length at home?

Yes, but home measurements are less accurate than clinic ones. Use the method above and the same technique each time.

Is length-for-age the same as height-for-age?

Length is measured lying down and is used under age 2. Height is standing and used from age 2.

Sources

• WHO Child Growth Standards
• CDC: WHO Growth Charts for children from birth to 24 months
• CDC: Growth chart percentile data files with LMS values

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• Height Percentile Calculator
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