21-month-old baby weight, length and head size
On the WHO growth charts, the median weight at 21 months is 11.5 kg (25.5 lb) for boys and 10.9 kg (23.9 lb) for girls. Most children of this age, between the 3rd and 97th percentiles, weigh 9.3–14.3 kg (20.6–31.5 lb) if they are boys or 8.7–13.8 kg (19.1–30.4 lb) if they are girls.
The median length at 21 months is 85.1 cm (33.5 in) for boys and 83.7 cm (32.9 in) for girls; between the 3rd and 97th percentiles it ranges over 79.7–90.5 cm (31.4–35.6 in) for boys and 77.9–89.4 cm (30.7–35.2 in) for girls. The median head circumference is 47.8 cm (18.8 in) for boys and 46.7 cm (18.4 in) for girls.
Since the age of 20 months, the median boy has gained about 0.2 kg (0.4 lb) and grown 0.9 cm (0.4 in), and the median girl about 0.2 kg (0.5 lb) and 1.0 cm (0.4 in).
WHO percentiles at 21 months
| P3 | P15 | P50 | P85 | P97 | |
|---|---|---|---|---|---|
| Weight (kg) Boys | 9.3 | 10.3 | 11.5 | 13.0 | 14.3 |
| Weight (kg) Girls | 8.7 | 9.6 | 10.9 | 12.4 | 13.8 |
| Length (cm) Boys | 79.7 | 82.2 | 85.1 | 88.1 | 90.5 |
| Length (cm) Girls | 77.9 | 80.5 | 83.7 | 86.8 | 89.4 |
| Head circumference (cm) Boys | 45.3 | 46.4 | 47.8 | 49.2 | 50.4 |
| Head circumference (cm) Girls | 44.1 | 45.3 | 46.7 | 48.2 | 49.4 |
These are WHO reference values, not targets: a healthy child can sit anywhere on the chart, and growth over time matters more than one measurement. Values outside the 2nd and 98th percentile lines are worth discussing with a doctor.
Work out your child's exact percentile
Frequently asked questions
How much should a 21-month-old weigh?
On the WHO charts, the median weight at 21 months is 11.5 kg (25.5 lb) for boys and 10.9 kg (23.9 lb) for girls; the 3rd to 97th percentiles span 9.3–14.3 kg (20.6–31.5 lb) for boys and 8.7–13.8 kg (19.1–30.4 lb) for girls.
How long should a 21-month-old be?
The median length at 21 months is 85.1 cm (33.5 in) for boys and 83.7 cm (32.9 in) for girls; the 3rd to 97th percentiles span 79.7–90.5 cm (31.4–35.6 in) for boys and 77.9–89.4 cm (30.7–35.2 in) for girls.
What head circumference is normal at 21 months?
The WHO median head circumference at 21 months is 47.8 cm (18.8 in) for boys and 46.7 cm (18.4 in) for girls, with 3rd to 97th percentiles of 45.3–50.4 cm (17.8–19.8 in) and 44.1–49.4 cm (17.4–19.4 in).
Other ages
- Newborn
- 1 month
- 2 months
- 3 months
- 4 months
- 5 months
- 6 months
- 7 months
- 8 months
- 9 months
- 10 months
- 11 months
- 12 months
- 13 months
- 14 months
- 15 months
- 16 months
- 17 months
- 18 months
- 19 months
- 20 months
- 21 months
- 22 months
- 23 months
- 24 months
- 3 years
- 4 years
- 5 years
Sources
- WHO: Child growth standards (weight-for-age, length/height-for-age, head circumference-for-age)
- Grummer-Strawn LM, Reinold C, Krebs NF. Use of World Health Organization and CDC growth charts for children aged 0–59 months in the United States. MMWR Recomm Rep 2010;59(RR-9)
- NHS: Your baby's weight and height