For children and young people aged between 2 to 18 years old, the BMI calculator takes into account age and gender as well as height and weight. To use the new tape test, measure your weight on a scale, then take a measurement of the circumference of your waist (abdomen) at the level of the belly button. The measurement should be in pounds (lbs) and inches (in).

Waist circumference is a better estimate of ‘visceral fat’. This is the dangerous internal fat that coats your organs.It’s good because it’s easy to understand. Doctors are more likely to use body mass index (BMI), a measure of weight relative to your height – use our BMI calculator. Waist measurement is better for people who carry a lot of muscle and less fat, like bodybuilders, boxers and rugby players. If you want to eat more healthily and lose weight, it’s best to measure how much weight you lose or put on. Losing weight will help your waist measurement too. People carry fat in different parts of their bodies. Some people carry extra body fat around their middle. This is more of a health risk than carrying weight on your hips and thighs. You will need to sit on an underwater mounted chair and scale. Once you have expelled all the air from your lungs, you will be lowered into a tank of water until fully submerged and remain motionless while the underwater weight is measured. The plus side: Keep an ongoing record of your measurements to monitor progress, every two weeks is usually sufficient frequency.

Measuring your waist can help reduce your risk of heart and circulatory diseases, as Professor Naveed Sattar tells Senior Cardiac Nurse Emily McGrath. Why does your waist measurement matter? DEXA is more commonly used to assess bone density, but can also be used to measure body composition. You lie still on a table while a machine arm passes over your entire body, which emits a high- and a low-energy X-ray beam.

The bottom line:

Famed for their reliability, excellent build quality and warranty, BMI is a private German company owned and run by the same family for over six decades. In their own words, the phrase 'made in Germany' means everything to them. Their main aim is to manufacture precision measurement tools that represent everything that phrase suggests... quality, durability, innovation and attention to detail. By measuring the absorption of each beam into parts of the body, technicians can get readings for bone mineral density, lean body mass and fat mass. The plus side: Expensive, in-a-lab methods are the most accurate; calipers probably give the best trade-off between cost, convenience and accuracy. But if you are just looking to monitor your progress, noticing how your clothes fit is as good as anything too.

For many people, reaching a ‘healthy’ weight is unrealistic. A weight loss of 5% (which means losing 5 kg if you currently weigh 100 kg) is more achievable. It will still result in important health improvements. Ideally measure on bare skin without clothing, if this is not possible measure wearing one thin layer of clothing. Measuring visceral fat can give a more accurate predictor of some health conditions. These include:

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For accurate readings you need to know where to place the measuring tape. It is only an estimate of body fat.