Weighing and Measuring a Child

To assess whether a child is a healthy weight, the first step is to obtain an accurate height and weight.

Equipment for Weighing and Measuring

The first step is to have the right equipment to obtain an accurate height and weight for the child.
To accurately calculate BMI you will need:

  • measuring equipment (ideally a Stadiometer with millimetre gradations)
  • scales (ideally electronic scales that weigh in kilograms, accurate to at least 0.1kg)
  • a calculator
  • girl and boy BMI charts.

Equipment calibration

When was the last time you heard a parent say, “that’s not what our home scales says he weighs”? It is important that weighing scales at any health or medical centre weigh accurately. It is important to have your weighing equipment calibrated at least annually. Digital scales are more accurate, though may need more frequent calibration.

There is less evidence regarding the frequency of calibration for stadiometers, although best practice would be to have these calibrated annually – at the same time as the weighing scales. Calibration of stadiometers would also be required if there were changes in circumstances, such as adding or removing carpet or moving the position of the stadiometer.

Preparation

Remember when preparing a child for weighing and measuring to ensure that the following items are removed:

  • shoes
  • hair ornaments that may impede measurement
  • hair bands if hair is tied up and likely to impede measurement
  • hats
  • heavy outer garments (coat, jacket, big jumper)
  • heavy articles in pockets

Measuring Weight

Points to remember when weighing a child

  1. Ensure the scales are placed on a hard surface, and not moved around too often.
  2. Press “on” button. Wait until scales show “0.0”.
  3. Ask child to stand:
    • centred on scales
    • feet evenly apart
    • hands by the side, not holding onto anything.
  4. Ask the child to look straight ahead and stand still.
  5. Read and record the measurement to nearest 0.1 kg. Write it immediately in the Child Health Record.
  6. If the display flashes between two weights even when the child is standing perfectly still (eg. 20.5kg and 20.6 kg) record the weight to the nearest 0.05 kg (eg 20.55kg).

If you have balance weighing scales, read the following information for instructions for correct use.

Instructions for using balance scales

  1. Ensure both weights are placed at zero.
  2. Ask child to stand:
    • centred on scales
    • feet evenly apart
    • hands by the side, not holding onto anything.
  3. Ask the child to look straight ahead and stand still.
  4. Slide the large weight slowly across the beam until you find a point at which the scales overweigh, then move the weight back one unit.
  5. Slide the small weight slowly across the beam, until the scales are nearly balanced (often indicated with a central pointer).
  6. Nudge the small weight gently until the scales are balanced. You may need to nudge the weight both backwards and forwards to achieve this.
  7. Combine the total weights and record the weight accurate to 0.1kg (100g). For example if the large weight was on 14kg and the small weight on 600g, the child’s weight would be 14.6kg.
  8. Write the measurement immediately in the Child Health Record.

Implications of inaccurate weighing

These inaccuracies could easily result in a child being wrongly classified. For example, children who are a healthy weight could be classified as being “overweight” and vice versa. Misclassification can cause:

  • unnecessary concern
  • inefficient use of resources, and/or
  • treatment not being provided where it is required.

For more detailed examples related to inaccuracies, see: Calculating and plotting BMI

Measuring Height 

Points to remember when measuring a child

  1. Bring the child over to the stadiometer and explain that you are going to measure their height.
  2. Ask and/or help child to stand:
    • up straight
    • feet and heels together
    • heels back against the upright section of the stadiometer
    • arms relaxed (floppy) by sides.
  3. Ask child to look straight ahead at marker on the wall. Arms should be relaxed by sides, with palms facing inwards. Gently position their head: hold your hand around their jaw, so that the top of their head and the stadiometer form a right angle and their chin is not pointing down towards their chest.
  4. Check that their head is still positioned correctly and their heels are still flat on the floor. Bring the set square down to rest on the child’s head.
  5. Crouch down so your eye is level with where the height is shown and record the measurement to nearest 0.1cm. Make a note of this measurement immediately.
  6. Ask the child to step off and step back onto the stadiometer and record a second measurement (you may be surprised by how much repeated height measures can differ). Take an average of these two measurements and record this in the Child Health Record.

Important note: If the two measurements disagree by 0.5cm or more, take a third measurement and calculate an average from the two closest measurements. Record this average in the Child Health Record.

Implications of inaccurate measuring of height

Inaccuracies in measuring height could easily result in a child being wrongly classified. For example, if an overweight child’s height is recorded as taller than they actually are, they could be classified as normal weight. On the other hand, a healthy weight child could be wrongly measured as shorter than they actually are and classified as overweight, which could then cause unnecessary concern and inefficient use of resources.

For more detailed examples related to inaccuracies, see: Calculating and Plotting BMI

Weighing, Measuring and Calculating BMI in Young Children

Why is weight important?

  • Being a healthy weight helps to optimise health outcomes
  • Overweight and obesity are associated with greater health risks, even in young children
  • The body mass index (BMI) is a measure of weight status that is used for children over 2 years of age.

Weighing

  1. Place the scales on a hard surface, and not moved around too often
  2. Press “on” button. Wait until scales show “0.0”
  3. Ask child to stand:
    • Centred on scales
    • Feet evenly apart
    • Hands by the side, not holding onto anything
    • Looking straight ahead and stand still.
  4. Read and record the measurement to nearest 0.1 kg (or to the nearest 0.05kg if the display flashes between two weights).

Measuring

  1. Explain to the child that you are going to measure their height
  2. Ask and/or help child to stand:
    • up straight
    • feet and heels together
    • heels back against the upright section of the stadiometer
    • arms relaxed (floppy) by sides
    • looking straight ahead at marker on the wall.
  3. Gently position their head so that their line of vision is parallel with the floor
  4. Check that they are in the correct position and bring the set square down to rest on the child’s head
  5. Crouch down so your eye is level with where the height is shown and record the measurement to nearest 0.1cm
  6. Ask the child to step off and step back onto the stadiometer and record a second measurement (you may be surprised by how much repeated height measures can differ)
  7. Take an average of the two measurements.

Important note: If the two measurements disagree by 0.5cm or more, take a third measurement and calculate an average from the two closest measurements. Record this average in the Child Health Record.

For an overview of this section, you can downloadWeighing, Measuring and Calculating BMI in Young Children (pdf - 46.25kb).