OunceChartOunces, sizes and milestones for the exact week or month.

Is 12.0 lb normal for a 13-month-old boy?

12 lb at 13 months
below the 1st percentile
for a boy on the CDC weight-for-age chart — below the 3rd percentile on the CDC chart
12 lb at 13 months19.8 lb5th percentile12 lbThis baby23.7 lbMedian28.4 lb95th percentile
PercentileBelow the 3rd percentile · CDC weight-for-agebelow the 1st
Weight5.44 kg — the unit the chart is built in12 lb
Z-scorestandard deviations from the median-6.57
Median for this age10.73 kg — the 50th percentile23.7 lb
5th percentile weight19.8 lb
95th percentile weight28.4 lb
Median length at this age77.3 cm30.4 in
Median head circumference46.8 cm18.4 in

Notes

  • The percentile is not a score, and the middle is not a target. By definition 5% of perfectly healthy children sit below the 5th percentile and 5% above the 95th, because the chart describes a population rather than prescribing a weight. A child at the 10th percentile who has been at the 10th percentile since birth is growing normally; the same child arriving there from the 60th over three months is the situation that gets attention. Clinicians watch the curve, not the point.
  • CDC recommends the WHO charts for children under 24 months, not this one. The WHO standard was built from exclusively breastfed infants under ideal conditions and describes how children should grow; the CDC chart describes how a mixed US sample did grow. In practice a breastfed baby often plots one or two bands lower on the CDC chart than on the WHO chart during the first year, which is a frequent and avoidable cause of worry. If your paediatrician's chart disagrees with this page in the first two years, that difference is very likely the reason.
  • Weight only means something next to length. A baby at the 15th percentile for weight and the 15th for length is proportionate; one at the 15th for weight and the 75th for length is a different picture entirely. Weight-for-length, plotted on its own chart, is what separates them, and it is the figure a check-up actually uses.
  • Corrected age matters if the baby was premature. Growth charts run from the due date, not the birth date, so for a baby born eight weeks early you plot at 13 months minus two. Doing otherwise makes a normally growing premature baby look as if it is falling behind, and correction is standard until about two years of age.
  • Measuring a baby accurately is harder than it sounds. Weigh naked or in a dry nappy of known weight, on the same scale, at roughly the same time of day; a feed and a nappy together can account for half a pound. Length needs two people and a firm surface — a tape measure along a wriggling baby is routinely out by an inch, which is enough to move the percentile by twenty points.

Where 12 lb sits for a 13-month-old boy

A weight of 12 lb (5.44 kg) at 13 months puts a boy at the below the 1st percentile on the CDC weight-for-age chart — below the 3rd percentile on the CDC chart.

The median for this age is 23.7 lb. The 5th percentile is 19.8 lb and the 95th is 28.4 lb, so the middle nine children in ten weigh somewhere between those two.

What a percentile is, and what it is not

A percentile compares one child to a reference population of children the same age and sex. The below the 1st percentile means roughly that share of children weigh less. It is a position on a distribution, not a mark out of a hundred, and there is no percentile that is the right one to be at.

The number that carries information is the direction of travel. A child who has tracked the same band since birth is growing the way that child grows. A child who crosses two bands downward over a few months is the one a check-up will want to look at, even if the new band is still comfortably inside the normal range.

Nearby sizes

Read more