[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Clinical exam](https://durgical.com/en/clinical-exam/) › [General exam and vital signs](https://durgical.com/en/clinical-exam/#a-general) › Weight, height, body mass index and waist circumference

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# Weight, height, body mass index and waist circumference

- Exam technique

How to weigh, measure height and work out body mass index, and why waist size matters too.

Updated 2026-11-01

## Key points

- BMI = weight in kilograms divided by height in metres squared.
- Adults (CDC): underweight below 18.5; healthy 18.5 to 24.9; overweight 25 to 29.9; obesity 30 or higher (class 1, 30 to 34.9; class 2, 35 to 39.9; class 3, 40 or higher).
- BMI is a screening tool: it does not separate muscle from fat or show where fat sits.
- Abdominal fat is assessed with waist circumference; cut-offs vary by population and guideline.
- Rapid weight gain over a few days is usually fluid (heart, kidney or liver disease), not fat.

## What it is

Anthropometry measures body size and composition: weight, height, body mass index (BMI) and waist circumference. It screens for undernutrition, overweight and obesity, tracks rapid weight changes from fluid retention and refines cardiometabolic risk. In children it is read on growth charts for age and sex, not with adult cut-offs.

## Landmark anatomy

- Waist: midpoint between the lower costal margin and the iliac crest, in the mid-axillary line.
- Height: from the vertex of the skull to the soles, with the head in the Frankfurt plane.

## Technique, step by step

- Weight: calibrated scale, light clothing, no shoes, ideally at the same time of day and after voiding.
- Height: standing barefoot, heels, buttocks and back against the stadiometer, eyes forward; lower the headpiece to the vertex.
- Calculate BMI and classify it with adult cut-offs or, in children, on the chart for age and sex.
- Waist: standing, abdomen bare, arms relaxed; find the midpoint between the lowest rib and the iliac crest.
- Run the tape horizontally, snug but not compressing, and read at the end of a normal breath out.
- In bedbound patients use a bed scale, or estimate height from knee height or arm span.
- Record units and technique; when tracking fluid, weigh daily under the same conditions.

## Abnormal findings

- Low BMI with unintended weight loss: undernutrition, cancer, tuberculosis, hyperthyroidism, uncontrolled diabetes or depression.
- Central obesity (large waist): higher risk of type 2 diabetes, hypertension and metabolic syndrome.
- Rapid weight gain with edema: fluid retention from heart failure, nephrotic syndrome or cirrhosis.
- In children, crossing down percentile lines: faltering growth or undernutrition (marasmus, kwashiorkor).

## Common errors

- Weighing in clothes, shoes or on different scales each day.
- Using the height the patient reports instead of measuring it.
- Measuring the waist over clothing or with a tilted tape.
- Applying adult cut-offs to children or adolescents.

## Test yourself

Think of the answer, then tap the question to see it.

## How is body mass index calculated?

Weight in kilograms divided by height in metres squared.

## What BMI defines obesity in adults according to the CDC?

A BMI of 30 or higher; 25 to under 30 is overweight.

## Where is waist circumference measured?

At the midpoint between the lowest rib and the iliac crest, with the tape horizontal, at the end of a normal breath out.

## What does a two-kilogram gain over two days suggest in a patient with heart failure?

Fluid retention and possible decompensation, not fat gain; that is why weight is checked daily under the same conditions.

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## Related

- [General inspection: appearance, posture, gait and consciousness](https://durgical.com/en/clinical-exam/general-inspection-appearance-posture-gait-and-consciousness/)
- [Edema: pitting, grading and distribution](https://durgical.com/en/clinical-exam/edema-pitting-grading-and-distribution/)
- [Pediatric history: perinatal, growth, development and vaccines](https://durgical.com/en/clinical-exam/pediatric-history-perinatal-growth-development-and-vaccines/)

## Related conditions

- [Obesity](https://durgical.com/en/conditions/obesity/)
- [Metabolic syndrome](https://durgical.com/en/conditions/metabolic-syndrome/)
- [Marasmus](https://durgical.com/en/conditions/marasmus/)
- [Kwashiorkor](https://durgical.com/en/conditions/kwashiorkor/)

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Educational content on the clinical exam; it is learned and practised under supervision. It does not replace assessment by a health professional and is not for self-diagnosis.

Sources: [Adult BMI Categories | BMI | CDC](https://www.cdc.gov/bmi/adult-calculator/bmi-categories.html) (Centers for Disease Control and Prevention, 2024); [Swelling: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003103.htm) (U.S. National Library of Medicine (MedlinePlus), 2025).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/clinical-exam/weight-height-body-mass-index-and-waist-circumference/