What's the best way to measure body fat? (2024)

Excess body fat could put your health at risk. Senior Dietitian Tracy Parker explains four key ways you can measure it.

Living with obesitycan increase your risk of heart problems. But it’s not just the number on the scales that counts.

Where the fat is in your body is important too. For example, fat around the belly (abdomen) is linked to higher risks of heart and circulatory diseasesand type 2 diabetes.

Having a lot of fat compared to the amount of muscle and bone you have in your body can also have a negative effect on your health.

There are many methods you can use to find out how much body fat you have and where it's located.

Some of these are simple and cheap to do, like weighing yourself on the bathroom scales or measuring your waist.

Others involve lab tests, which offer detailed results but can be expensive.

Here's our guide to your options.

1. Using your total body weight

Weighing yourself is one of the first steps you can take to check if you’re a healthy weight.

But how does knowing your total body weight help with knowing how much fat you have?

Let's take a closer look at two of the most common methods.

Weighing scales

What they measure:

Stepping on the scales is one of the simplest ways to see if you're carrying excess weight.

They measure your total body weight that includes your bones, muscle, blood, organs and fat.

They cannot tell you:

• how much of your weight is made up of fat and how much is bone or muscle
• where fat is located.

So, while scales can help you track your weight over time, they do not give you the full story.

For example, your overall weight may not go down even though you’re losing fat, because you may also be gaining muscle as you make healthy lifestyle changes.

• Read more on how yourweight affects your health.

How to use them:

• Make sure to use reliable scales for accurate results.
• If you’re tracking your weight over time, try to weigh yourself at the same time of day, under the same conditions and on the same set of scales. This could be in the morning, after emptying your bladder.

Body Mass Index (BMI)

What it measures:

Your BMI uses your total body weight and your height to work out if you’re a healthy weight.

However, your BMI cannot tell you where fat is located in your body.It also cannot tell the difference between muscle and fat.

This means it may be misleading for people who are elderly, have a lot of muscle or are pregnant.

How to work it out:

1. Use reliable weighing scales to measure your weight in kilograms.
2. Use a tape measure to work out your height in metres.
3. Divide your weight by your height multiplied by itself (squared) to work out your BMI.

Or you can work out out your BMI with ourfree BMI calculator tool.

What it means:

For most adults, the higher the BMI figure, the more excess weight you’re carrying, and the greater the health risks.

If you’re from a Black African, African Caribbean, South Asian, Chinese, Middle Eastern or mixed family origin, you may have a higher risk of health problems at a lower BMI than people from white populations.

There are four BMI categories (kg/m2):

• Healthy weight: 18.5 to 24.9 (white population) and 18.5 to 22.9 (other ethnicities).
• Overweight: 25 to 29.9 (white population) and 23 to 27.4 (other ethnicities).
• Obesity: 30 and above (white population) and 27.5 and above (other ethnicities).
• Underweight: Less than 18.5.

2. Measuring fat around the belly

You can have a healthy BMI and still have excess fat around the belly (abdomen). This means that you're still at risk of heart and circulatory diseases and type 2 diabetes.

Here are a few ways you can measure fat around your waist.

Waist to height ratio

What it measures:

This compares the difference between the size of your waist (the circumference) and your height to see if you’re carrying too much fat around your belly.

A smaller difference means you’re carrying more fat around your waist.

How to do it:

1. Wrap a tape measure around your waist between the bottom of your ribs and top of your hips. For most people this is just above the belly button.
2. Breathe out naturally, then take a note of the number where the tape measure reaches all the way round. This can be in centimetres or inches.
3. Measure your height in centimetres or inches. Use the same tape measure you used to measure your waist.
4. Divide your waist measurement by your height to find your waist to height ‘ratio’.

For example, 38 inches divided by 67 inches would equal a waist to height ratio of 0.57.

What it means:

The smaller the difference between your waist and height, the higher the ratio.

A waist to height ratio over 0.5 to 0.59 suggests you have an increased risk of health problems. If your ratio is 0.6 or above, your risk is even higher.

The 'string challenge':

The ‘string challenge’ is another way to compare the size of your waist to your height.

1. Measure your height with a piece of string.
2. Cut or mark the string so it's the same length as your height.
3. Fold the length of string that matches your height in half.
4. Wrap the folded string around your waist and check if it fits all the way around.

If the folded string is not long enough to wrap around your waist, this is a sign that you have excess fat around your belly.

• Read more about risk factors for heart disease.

Waist to hip ratio

What it measures:

Did you know that the shape of your body could help tell you how much abdominal fat you have?

• 'Apple' shape – this is when your waist is nearly as wide or wider than your hips and suggests you have a lot of fat stored around your waist.
• 'Pear' shape – this is when your hips are wider than your waist and suggests you have a lot of fat stored around your hips or buttocks, and less around the belly.

An 'apple' shape, with more fat around the belly, can come with a higher risk of health issues. By working out the difference between the size of your waist (waist circumference) and the size of your hips (hip circumference), you can find your waist to hip ratio.

If the size of your waist is nearly the same or larger than your hips, the ‘ratio’ will be higher, which suggests that more fat is stored around the belly.

How to work it out:

1. Measure the circumference of your hips by wrapping a tape measure around the widest point of your buttocks.
2. Then measure your waist at the midpoint between the bottom of your ribs and the top of your hips.
3. You can use either inches or centimetres, but make sure to use the same for both.
4. Then, divide the measurement around your waist by the measurement around your hips to find out the ratio.

What it means:

A higher ratio could increase your risk of heart and circulatory diseases and type 2 diabetes.

• High risk for men: Above 0.90
• High risk for women: Above 0.85

3. Calculating your body fat percentage

Your body fat percentage is the amount of your total body weight that's made up of fat. A higher percentage of body fat can increase your chance of heart and circulatory diseases.

So, while you may have a healthy BMI, if more of your weight is made up of fat, you may still be at risk of health problems.

If you're interested in finding out the percentage of your weight made up of fat, there are a few tools you can use.

Skinfold calipers

What they measure:

Skinfold calipers measure fat underneath the skin (subcutaneous fat) at certain places on your body. These are known as 'skinfold measurements' and you can use them to estimate your percentage of body fat.

A set of calipers can cost from as little as £4 to £10 online, so it's a relatively cheap way to measure body fat.

How to use them:

1. Use the calipers to pinch the skin and pull the fat away from the muscle. You can measure yourself or ask someone else to do it for you.
2. The calipers measure the thickness of this fold of skin, usually in inches or millimetres. A higher number can be a sign of excess body fat.
3. You can measure the skin on your thigh, just above your hip bone, back of your arm (tricep), belly, just below your shoulder blade, chest and armpit.
4. Check each spot at least twice in the same session, and always use them on the same side of your body.

What it means:

The measurements can be used to track body fat over time. If your skinfold thickness is going down, then you’re probably losing fat.

However, calipers may not always be reliable, and can be tricky to use with some sets more accurate than others.

Smart scales

What they measure:

Often found at the gym, you can use smart scales to work out how much of your weight is made up of body fat.

They look like normal scales with foot plates and may have additional hand plates. They use a process known as bio impedance that sends tiny electrical impulses through the body and measures how quickly they return.

This works because the electrical current flows more easily through parts of the body mostly made up of water, such as muscle and blood, compared to fat or bone.

How to use them:

• Simply stand on the scales, and hold the hand plates if there are some, to get an estimate of your body fat percentage instantly.
• If you're tracking your progress over time, measure yourself at the same time of day in similar conditions for more reliable results.
• Make sure you drink plenty of water before you use them, as they can overestimate the amount of body fat if you're dehydrated.

While some smart scales can be pricey, you can buy cheaper models from around £25, or check to see if your local gym has some you can use. You can also find a range for sale on the British Heart Foundation online shop.

However, if you have a pacemaker, smart scales are not suitable for you.

• Learn more about devices you should avoid if you have a pacemaker.

4. Testing in a lab

If you're looking for a highly accurate way to measure your body fat, there are a few options available.

However, these methods are usually expensive and harder to access.

DEXA scan

What it measures:

DEXA (Dual Energy X-ray Absorptiometry) is more commonly used to assess bone density, but it can also be used to measure body fat.

It can tell you how much fat you’re carrying and how it’s distributed around your body.

How it works:

1. You lie still on a table while a machine passes over your entire body and emits a high- and a low-energy X-ray beam.
2. The scan usually takes around four minutes.
3. By measuring how each beam is absorbed into parts of the body, the scan can work out how much bone, muscle and fat your body is made up of.

You can access a DEXA scan at private clinics around the UK. However, one scan usually costs at least £100.

Underwater weighing

What it measures:

Underwater weighing, also known as hydrostatic weighing, measures your body density, which is then used to estimate how much fat you have.

Fat is less dense than bone and muscle, so someone with a higher percentage of fat will weigh less under water, and float more easily.

How it works:

1. First, you sit on an underwater mounted chair with weighing scales.
2. Once you have exhaled all the air from your lungs, you’ll be lowered into a tank of water until you're fully underwater and remain still while your weight is measured.
3. You need to be fully submerged for five to seven seconds, two to three times, so it’s not suitable for elderly people or children.

While it offers highly accurate results, most tanks are located at universities or research institutions, so they are hard to access and can cost hundreds of pounds.

Air displacement

What it measures:

A scan called ‘BOD POD’ uses technology known as Air Displacement Plethysmography to measure body density.

It’s like underwater weighing but with air instead of water.

How it works:

1. You sit in a small ‘pod’ machine, which measures how much you weigh (mass) with weighing scales.
2. The machine also measures how much space your body takes up (volume) by working out how much air is pushed out when you get in the pod.
3. These measurements are used to calculate your body density, which can then be used to work out your body fat percentage.

The scan is accurate, quick and works outside your body.

However, this technology is mainly found in research institutions, so it's hard to access.

And while it's cheaper than underwater weighing, it can be costly, with prices starting at £40 per scan.

• Read our 10 tips for weight loss.

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Updated 21 May 2024