How to measure your baby for a growth chart

Start with the date and the unit

Write down when each measurement was taken and whether it is in pounds and ounces, kilograms, inches, or centimeters. In our calculator, the measurement date should be the day the number was taken. Do not use today’s date for a number from an earlier checkup.

You can enter weight, length, or head circumference on its own. You do not need all three. If you enter more than one, use measurements taken on the same date.

The calculator uses your baby’s birth date and measurement date to find their age in days. The CDC says accurate measurements and correct age are important when using growth charts.

Weight: use a baby scale

A recent weight from your pediatrician’s office is a useful place to start. Health workers use a scale and a consistent method. Cambridge University Hospitals gives parents advice about home weighing.

If you weigh your baby at home, use a scale made for babies and follow its instructions. Record the number and unit shown. In our calculator, choose U.S. to enter pounds and extra ounces, or Metric to enter kilograms. Do not round a number from memory if you have the exact reading.

If your home reading looks very different from a checkup reading, check the date and units first. Ask your pediatrician which measurement to use if you are unsure.

Length: measure while your baby lies down

For babies younger than 2, the growth chart uses lying-down length. This is different from standing height. The CDC explains which measurement belongs on the chart, and Cambridge University Hospitals offers parent instructions for measuring length at home.

Length can be hard to measure while a baby moves. If you do not have a careful lying-down measurement, leave length blank and use another measurement you know. You can ask your pediatrician’s office for the length from your baby’s latest visit.

Head size: measure around the widest part

Head circumference is the distance around your baby’s head. The CDC shows how a non-stretch tape is placed: above the eyebrows and ears, and around the most prominent part at the back of the head.

Use a head measurement from your pediatrician’s office if you are not sure where to place the tape. Do not use a hat size as a substitute.

Before you calculate

Check these four details:

1. Is the birth date correct?
2. Is the measurement date the day the number was taken?
3. Did you choose the right unit for each number?
4. If you entered several measurements, were they taken on the same day?

If a result surprises you, check those details before calculating again. A single number cannot show your baby’s growth pattern. The AAP explains that pediatricians look at measurements over time.

Our calculator is for babies younger than 2 who were born at 37 weeks or later. If your baby was born earlier, ask your pediatrician which chart and age to use. You can read more in How this calculator works.