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Accurate measurement of patient height is required for the assessment of body mass index which is an important part of routine nutrition screening of patients
This practical procedure, the second of a two-part series, explains the rationale for measuring patients’ height, outlines the procedure and explains how weight and height are used to calculate body mass index. Part 1 focused on weighing patients.
Citation: Best C, Shepherd E (2020) Accurate measurement of weight and height 2: calculating height and BMI. Nursing Times [online]; 116: 5, 42-44.
Author: Carolyn Best is nutrition nurse specialist, Hampshire Hospitals NHS Foundation Trust; Eileen Shepherd is clinical editor, Nursing Times.
Malnutrition is a common problem found in all care settings. As part of nutrition screening, height and body weight should be recorded:
- On admission to hospital or pre-assessment clinics;
- At outpatient appointments;
- On admission to care homes;
- In GP surgeries (National Institute for Health and Care Excellence, 2006).
The procedure for measuring a patient’s height is required to accurately calculate their body mass index (BMI), which should form part of a comprehensive nutrition screening tool, such as the Malnutrition Universal Screening Tool (MUST) (Malnutrition Action Group, 2011). This procedure is often delegated to junior staff but it is important that all staff have received training and understand the rationale for carrying it out.
Before attempting the procedure, you should check the patient is able to stand upright (Dougherty and Lister, 2015). If this is not possible, their height can be estimated using their ulna length or knee height and converting the measurement using a standardised chart (Tables 1 and 2) or online calculator (for example, Bit.ly/MUSTCalculators).
Patients may be able to tell you their height but it is important to remember that older people lose height as part of the ageing process, so this may be inaccurate (Knight et al, 2017). A metric–imperial conversion chart is useful, as patients often report or want to know their height in imperial measurements.
Height is measured using a metric stadiometer; this is usually attached to a wall (Fig 1) but may be freestanding. The stadiometer should be calibrated according to local policy. A tape measure – in centimetres – is required to measure ulna length or knee height. It should be disposable or suitable for cleaning between patients, following local policy.
Infection prevention precautions
Measuring equipment that is used on several patients presents an infection risk and should be cleaned after use, according to local policy. Patients who have an infection may still require their height to be measured; local infection prevention teams can offer advice on specific precautions in these circumstances.
Non-sterile gloves are not required routinely for this procedure. Nurses need to assess individual patients for the risk of exposure to blood and body fluids (Royal College of Nursing, 2018) and be aware of local policies for glove use.
- Review the patients notes and identify the rationale for measuring their height – this will help you to interpret the results.
- Discuss the procedure with the patient and gain verbal informed consent.
- Assess the patient’s mobility and ability to stand unassisted then select the appropriate method for measuring or estimating height.
- Screen the bed to maintain patient privacy and dignity, and ask them to remove heavy outdoor clothing so you can visualise their position.
- Check the equipment has been cleaned and decontaminate your hands according to local policy. An apron should be worn if the patient needs physical assistance to get out of their bed or chair.
- Ask the patient to remove their shoes.
- Position the patient with their back to the measuring rod on the stadiometer, ensuring their feet are together and facing forward and their heels are touching the heel plate or wall (Dougherty and Lister, 2015) (Fig 1). The patient’s knees should be straight, and their shoulders, buttocks and head should touch the stadiometer.
- Ask the patient to look straight ahead and adjust the head plate until it touches the top of their head. You may need to press down gently on the patient’s hair (Fig 1).
- Record the patient’s height to the nearest centimetre in the relevant documentation.
If a patient is unable to stand, height can be estimated using the ulna length or knee height (MAG, 2011).
- Ask the patient to remove any watches or jewellery from the left wrist. Remove clothing from the shoulder to the wrist so you can clearly identify measurement ‘landmarks’.
- Position the patient’s left arm across their chest with palm flat and the hand pointing to the right shoulder (Fig 2). The left arm is used as the MUST equations were validated for use on the left side; if it is not possible to use the left arm, use the right arm and note this in the patient’s records; (MAG, 2011).
- Measure the length from the olecranon process of the elbow to the midpoint of the styloid process of the wrist (Fig 2).
- Record this measurement to the nearest 0.5cm and use a conversion chart to estimate height (Table 1 and Box 1).
- Measure the left leg if possible; the MUST equations were validated for use on the left side (MAG, 2011).
- Help the patient to remove any footwear and adjust clothing so their leg is exposed below the knee.
- Help the patient to sit in a chair with their knee at a right angle.
- Hold a tape measure between your third and fourth fingers and place your hand flat across the thigh and about 4cm behind the front of the knee (MAG, 2011) (Fig 3).
- Position the tape measure down the side of the leg, in line with the lateral malleolus (ankle bone), to the base of the heel (MAG, 2011) (Fig 3).
- Record this measurement to the nearest 0.5cm and use a conversion chart to calculate the height (Table 2 and Box 2).
- Record in the relevant medical records the patient’s estimated height and the method used to obtain this measurement.
- Explain your finding to the patient and any action you plan to take.
- Dispose of, or clean, the equipment according to local policy.
- Decontaminate your hands.
Calculating body mass index
Body mass index (BMI) is a measure of body fat derived using a patient’s weight and height. BMI classifications are:
- <18.5 – underweight;
- 18.5-24.99 – normal;
- 25-29.99 – overweight;
- >30 – obese.
The formula to calculate BMI is given in Box 3. Alternatively, a BMI calculator (such as that at) can be used but is important to ensure it is accurate and approved for use by your employing organisation.
Accuracy of BMI
There are certain patients whose bone structure and muscle mass will result in a high weight (for example weightlifters), which will cause them to have a high BMI that classifies them as obese; in contrast, some athletes may have a very low BMI. It is, therefore, important that any measurements taken are not viewed in isolation; it is imperative that they form part of a comprehensive nutritional assessment, such as MUST (MAG, 2011).
When it is not possible to measure weight and height to calculate a patient’s BMI, the mid-arm circumference measure can be taken, although this is not commonly used in practice. MAG (2011) states that this measurement provides a general indication of BMI, not an actual score. For further information on this measurement, see MAG (2011).
Dougherty L, Lister S (2015) The Royal Marsden Hospital Manual of Clinical Nursing Procedures. Wiley-Blackwell.
Knight J et al (2017) Anatomy and physiology of ageing 10: the musculoskeletal system. Nursing Times; 113: 11, 60-63.
Malnutrition Action Group (2011) The ‘MUST’ Explanatory Booklet: A Guide to the ‘Malnutrition Universal Screening Tool’ (‘MUST’) for Adults. BAPEN.
National Institute for Health and Care Excellence (2006) Nutrition Support for Adults: Oral Nutrition Support, Enteral Tube Feeding and Parenteral Nutrition. NICE.
Royal College of Nursing (2018) Tools of the Trade: Guidance for Health Care Staff on Glove Use and the Prevention of Contact Dermatitis. RCN.