At a glance
Taking accurate height and weight measurements is essential for correct body mass index (BMI) and BMI percentile calculations. Follow these steps when measuring children's height and weight.
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How to measure height accurately
Follow these steps to measure a child's height accurately.
- Remove the child's shoes, bulky clothing, hats, and hair ornaments. Undo hairstyles that interfere with getting an accurate height measurement.
- Have the child stand:
- On firm flooring, such as tile or wood rather than carpet.
- Against a flat surface, such as a wall with no molding.
- With their feet flat, together, and against the wall.
- With legs straight, arms at their sides, and shoulders level.
- On firm flooring, such as tile or wood rather than carpet.
- Make sure the child is looking straight ahead.
- Measure while the child stands with their head, shoulders, buttocks, and heels touching the flat surface, usually a wall. Depending on the child's body shape, all points may not touch the wall.
- Use a flat and rigid ruler or book to form a right angle with the wall.
- Lower the ruler or book until it firmly touches the crown (very top) of the child's head.
- Make sure the eyes of the person measuring are at the same level as the ruler or book.
- Lightly mark where the bottom of the ruler or book meets the wall.
- Measure the distance between the base on the floor and the mark on the wall using a metal tape measure.
- Accurately record the height to the nearest 1/8th inch or 0.1 centimeter (for example, 35.2 inches).
How to measure weight accurately
Follow these steps to measure a child's weight accurately.
- Use a digital scale. Avoid using spring-loaded bathroom scales.
- Place the scale on firm flooring (such as tile or wood) rather than on carpet.
- Have the child remove shoes and heavy clothing, such as sweaters.
- Have the child stand with both feet in the center of the scale.
- Record the weight to the nearest decimal fraction (for example, 55.5 pounds or 25.1 kilograms).
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How to calculate BMI and BMI percentile
To calculate BMI and BMI percentile for children and teens 2 through 19, use CDC's BMI Calculator for Child and Teen. The calculator also plots BMI percentile on a CDC growth chart and explains the results. The calculator is not a substitute for professional medical advice.
To calculate BMI for adults 20 or older, use CDC's Adult BMI Calculator.
To calculate BMI by hand, use the formulas below:
- Metric Units: weight (kg) / [height (m)]2
- Metric Units: [weight (kg) / height (cm) / height (cm)] x 10,000
- U.S. Customary Units: weight (pounds) / [height (in)]2 x 703