acalculator

What is my child’s height percentile?

Enter your child’s sex, age and height to see their height-for-age percentile on the WHO growth standards (under 2, measured lying down) or the CDC growth charts (2 to 20).

Your numbers

Units
Sex
Based on
Height percentile
56.1

At 4 years, a height of 40.5 in is at percentile 56.1 on the CDC stature-for-age (2 to 20 years) chart.

Z-score
0.15
Median height at this age
40.2 in
5th percentile height
37.5 in
95th percentile height
43 in
Screening range
Between the 5th and 95th percentiles
Age
4 years
Growth chart
CDC stature-for-age (2 to 20 years)

Answer for the example date Wednesday, September 30, 2026. It changes to today's date when the page loads.

Height percentile: 56.1. At 4 years, a height of 40.5 in is at percentile 56.1 on the CDC stature-for-age (2 to 20 years) chart.

Where does this height sit among children of the same age?

This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use

How to calculate

Finds a child’s height-for-age (or length-for-age) percentile and z-score from birth to 20 years, on the WHO growth standards under 24 months and the CDC growth charts from 2 years.

Example with the default inputs (Sex Boy, Based on Age, Years 4, Months 0, Height 40.5 in) on the example date Wednesday, September 30, 2026: At 4 years, a height of 40.5 in is at percentile 56.1 on the CDC stature-for-age (2 to 20 years) chart.

Method: z = ((height ÷ M)^L − 1) ÷ (L × S), height in cm; percentile = Φ(z) × 100, with L, M and S for the sex and age from the WHO length table under 24 months and the CDC stature table from 24 months, read on a straight line between table ages.

  • Under 24 months the page uses the WHO 2006 length-for-age standard (measured lying down); from 24 months to 20 years, the CDC 2000 stature-for-age chart (measured standing), as the CDC advises for US children.
  • Age in months is 12 × years + months, or the days from birth to the measurement ÷ 30.4375.
  • The percentile is rounded half up to one decimal place and shown between 0.1 and 99.9.
  • A percentile compares a child with a reference group. It is not a diagnosis; a doctor looks at growth over time.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Sex Girl, Based on Age, Years 1, Months 0, Height 31.17 in gives Height percentile 97.7, Z-score 2, Median height at this age 29.1 in, 5th percentile height 27.5 in, 95th percentile height 30.8 in, Screening range Between the 2.3rd and 97.7th percentiles, Growth chart WHO length-for-age (birth to 24 months).Source: WHO length-for-age, girls, month 12 (CDC copy of the WHO table): L 1, M 74.015, S 0.03479
  2. Sex Boy, Based on Age, Years 12, Months 6.5, Height 58.08 in gives Height percentile 25, Z-score -0.67449, Median height at this age 60.1 in, 5th percentile height 55.2 in, 95th percentile height 65.2 in, Growth chart CDC stature-for-age (2 to 20 years).Source: CDC statage.csv, boys, 150.5 months: L 0.531951655, M 152.6623878, S 0.050273285, P25 147.5268957 cm
  3. Sex Girl, Based on Age, Years 12, Months 0, Height 60 in gives Height percentile 56.5, Z-score 0.164269, Age 12 years.Source: CDC statage.csv, girls, 144 months (between the 143.5 and 144.5 rows): a 5 ft (152.4 cm) girl

How it works

1. Age in months. Enter the age as years and months (months may have decimals), or as a birth date and a measurement date:

  • age in months = 12 × years + months, or
  • age in months = (measurement date − birth date, in days) ÷ 30.4375.

No answer if the measurement date is before the birth date, or if the age is over 240 months (20 years).

2. The chart. Under 24 months the calculator uses the WHO length-for-age standard (measured lying down); from 24 months to 240 months, the CDC 2000 stature-for-age chart (measured standing). Both tables are used exactly as published, in centimetres:

  • WHO: one row per whole month, 0 to 24, with L, M and S for boys and for girls (L is 1 in every row).
  • CDC: rows at 24 months, then at 24.5, 25.5, 26.5 and so on up to 239.5, then at 240 months.

3. L, M and S at the age. At a table age the row is used as it is. Between two table ages a₀ < a < a₁, each of L, M and S is read on a straight line: L = L₀ + (a − a₀) ÷ (a₁ − a₀) × (L₁ − L₀), and the same for M and S.

4. The z-score and percentile, with the height x in centimetres:

  • z = ((x ÷ M)^L − 1) ÷ (L × S), or z = ln(x ÷ M) ÷ S if L is 0;
  • percentile = Φ(z) × 100, where Φ is the standard normal cumulative distribution.

The percentile is rounded half up to one decimal place (the decimal value decides) and then kept between 0.1 and 99.9. The z-score is shown to two decimal places.

5. Other rows.

  • Median height at this age = M.
  • 5th and 95th percentile heights = M × (1 + L × S × z)^(1/L) with z = −z₉₅ and +z₉₅, where z₉₅ = Φ⁻¹(0.95), the exact inverse normal value 1.6448536269514727… (the engine uses the nearest double, 1.6448536269514729).
  • Screening range, read from the shown percentile p: on the WHO chart, "Below the 2.3rd percentile" if p < 2.3, "Above the 97.7th percentile" if p > 97.7, otherwise "Between the 2.3rd and 97.7th percentiles"; on the CDC chart, the same with 5 and 95 ("5th", "95th").
  • Age: the age in months rounded half up to one decimal place, written as years and months.
  • Growth chart: "WHO length-for-age (birth to 24 months)" or "CDC stature-for-age (2 to 20 years)".

The chart on the page shows the standard normal curve with the area to the left of the child’s z-score shaded: that area is the percentile.

Rounding. Every “rounded half up” on this page reads the decimal value: a result within 1e-9 (relative) of a half counts as the half. For example, 80 ÷ 1.6², which a computer stores as 31.249999999999993, rounds to 31.3.

Assumptions

  • Φ is computed with Marsaglia’s series (J Stat Softw 2004), which matches the exact value to within 5e-15; percentiles beyond z = ±8 show as 0.1 or 99.9.
  • The WHO standard describes healthy breastfed babies; the CDC chart describes US children measured from 1963 to 1994. The CDC advises the WHO standard under 2 years and its own chart from 2.
  • One measurement is a snapshot. Doctors look at the pattern over several visits.
  • This calculator gives general information. It is not medical advice or a diagnosis; talk to your child’s doctor about their growth.

Worked examples by hand

A girl of 1 year (12 months) who is 79.1649637 cm (31.2 in) long. The WHO girls’ row for month 12 is L = 1, M = 74.015, S = 0.03479. With L = 1, z = (79.1649637 ÷ 74.015 − 1) ÷ 0.03479 = 0.069580 ÷ 0.03479 = 2.00, so the percentile is Φ(2) × 100 = 97.72, shown as 97.7: between the 2.3rd and 97.7th percentiles (97.7 is not above 97.7). The median is 74.015 cm; the 5th and 95th percentile lengths are 74.015 × (1 ∓ z₉₅ × 0.03479) = 69.78 and 78.25 cm.

A boy of 12 years 6.5 months (150.5 months) who is 147.5268957 cm (58.1 in) tall. The CDC boys’ row for 150.5 months is L = 0.531951655, M = 152.6623878, S = 0.050273285. (147.5268957 ÷ 152.6623878)^0.531951655 = 0.981962; minus 1 = −0.018038; ÷ (0.531951655 × 0.050273285 = 0.026743) gives z = −0.6745, the 25th percentile: 25.0. The 5th and 95th percentile heights are 140.28 and 165.53 cm.

A girl of exactly 12 years (144 months) who is 5 ft (152.4 cm) tall. 144 months is halfway between the CDC girls’ rows for 143.5 and 144.5 months, so each of L, M and S is the average of the two rows: L = 1.288525, M = 151.190105, S = 0.048772. z = ((152.4 ÷ 151.190105)^1.288525 − 1) ÷ (1.288525 × 0.048772) = 0.1643, and the percentile is 56.5. The age reads "12 years".

Other questions people ask

What does a height percentile mean?

It is the share of children of the same sex and age in the reference group who are shorter. A girl at the 40th percentile is taller than 40 of every 100 girls her age on the chart.

Why is a baby’s length used instead of height?

Under 2 years, children are measured lying down (length), and the WHO length-for-age standard uses those measurements. From 2 years, the CDC stature-for-age chart uses standing height. A child is usually about 0.7 cm (0.3 in) shorter standing than lying down, so the switch at 24 months can move the percentile a little.

What is a normal height percentile?

Children of healthy height can be at any percentile. What matters most is a steady pattern over time. For screening, the CDC suggests the 2.3rd and 97.7th percentiles on the WHO charts and the 5th and 95th on the CDC charts. A doctor may look more closely at a child outside those, or one who crosses percentile lines.

Can I use this for adults?

No. The charts end at 20 years. Adult heights are compared with national survey data, not with growth charts.

How accurate is the percentile?

The maths follows the published WHO and CDC tables exactly. The measurement is the weak point: an error of 1 cm can move a percentile by several points. Measure without shoes, heels together, looking straight ahead.

Does a tall child grow into a tall adult?

Often, but not always. Timing of puberty moves children up and down the chart in their early teens. For a rough adult height from the parents’ heights, see the height calculator.