How Medical Scales Calculate Body Fat


Weight and body fat percentage are important metrics in terms of measuring the efficacy of your fitness and diet and can also be used to identify potential health issues.

Conventional floor scales can be found in many bathrooms across the UK; however, these are often limited to only measuring an individual’s weight.

Monitoring body fat is important as it can allow you to understand the effectiveness of your diet and fitness regime. In more serious cases, exceeding healthy fat levels can even increase the likelihood of developing health problems such as heart disease and diabetes.

Marsden Body Composition Scale 2

Historically, advanced machinery was required to calculate your body fat percentage, but now, technological advancements have enabled the same measurements to be obtained from compact, affordable scales.

So, how do body fat scales actually work?

The majority of modern body fat scales utilise a technology known as ‘bioelectrical impedance analysis’.

Put simply, this involves the transmission of a weak (and essentially unnoticeable) electric current passing through a person’s body, starting from one foot and ending at the other.

How does this equate to body fat percentage?

Different materials have varying levels of electrical conductivity (how well the movement of electricity can be facilitated) and, in the case of a human body, fat stores are much less conductive than muscle tissue and other areas of the body.

Scales are able to record and analyse any resistance encountered by the electrical current after each session and convert this into a percentage.

The higher the resistance, the more fat in your body.

Why is this important?

As mentioned previously, high levels of body fat can be a harbinger for developing numerous different health problems in the future.

However, it can be hard to ascertain whether or not you should be concerned from simply looking in the mirror or tracking your standard weight measurements.

Having a high body fat percentage is an issue which can affect overweight people as well as those with a normal body mass index (BMI). This is because fat can be stored in many different places in our bodies and can often hide away in other areas than just your stomach.

By obtaining a true measurement of the amount of body fat in your system, informed lifestyle changes can be made which will help to improve your overall health such as eating different (or specific) foods and choosing an optimal exercise strategy.


Potential Limitations

Body fat scales can be a great way to monitor your weight loss endeavours, especially if you are consistent in the equipment used and the time of day you take these measurements.

With that being said, however, there are a few limitations of domestic body fat scales.

As this type of equipment is actually measuring electrical resistance instead of directly calculating body fat percentage, there are a number of common factors which can affect the accuracy of your measurements.

For instance, fluctuating hydration levels, body type (endomorph, mesomorph and ectomorph) and temperature are all unrelated to your body fat percentage, yet can still affect the scales reading by increasing or decreasing electrical resistance.

In addition, most scales only take a reading of resistance found in the lower half of your body as the current does not travel through to the torso, arms or other upper regions. This is an inherent characteristic of body fat scales which can hinder their accuracy.



Body fat scales are excellent tools for identifying trends in your weight and can help to gauge the success of any fitness activities you engage in.

You can maximise their effectiveness and accuracy by ensuring any measurements are taken at the same time of day and by removing as many variables as possible.

However, it is always best to seek attention from your doctor in order to obtain a true reading of your body fat percentage as they will be able to provide you with expert advice in addition to using the most sophisticated weighing technology.

Learn about the Marsden MBF-6020 Body Composition Scale, available now at Solent Scales, by clicking here.