How to Calculate Your Body Fat Percentage – and What it Means

Is there an ideal body fat percentage for women? Here's what the science says – and what lower isn't always better.

Knowing the correct body fat percentage for women might sound a little too heavy on the science for the non-athletes of us out there.

But understanding this can be helpful when it comes to knowing that your physique is in an okay place.

As the late biologist Rose Frisch discovered in her research, evaluating weight alone can be misleading – as muscles are heavy (80% water compared to 5-10% water in fatty tissue), meaning that many athletes she analysed appeared in the ‘normal’ weight range, despite having no periods, as a direct consequence of their body composition aka r excessive leanness.

On the flip side of this, people with a low muscle mass and an unhealthily high body fat percentage open themselves up to health risks, illnesses and ailments. More on this to come.

So. How to know what's a good place to be resting at? Here's the lowdown.

What is body fat?

Body fat is measured by percentage, calculated by how much body fat you have in relation to the rest of your body (like your bones, muscle mass, organs, etc.).

While body fat percentage can be a fairly useful indicator of health – as mentioned, both high and low body fat are associated with certain health risks.

Is your BMI or body fat percentage a better measure of health?

Depends who you ask. The NHS uses BMI (body mass index), which requires no special tools or tech to calculate. Working it out is simple: just divide your weight in kilograms by your height in metres squared.

As you've likely heard, BMI is not a perfect measure – for example, it fails to account for muscle mass, which, of course, body fat percentage does.

However, unless professionally done, body fat percentage measures are pretty inaccurate (sorry, fancy scale at your gym). Overall measures of body fat also usually don't pinpoint where on the body excess fit sits.

'Distribution of fat, which can be more important when assessing risk of disease,' Dr Frankie Jackson-Spence, NHS doctor, says. 'For example fat distributed centrally around your organs is more of a risk factor for metabolic diseases than subcutaneous fat elsewhere.'

How to measure body fat percentage for women

Is there a way to calculate your own body fat percentage? There are several – many of which can be done at home and without eye-watering costs. But (there's always a but, isn't there?) as previously mentioned, you're not going to have an exact figure without the help of medical professionals and a stint in a lab.

Here are some of the options available.

Body fat percentage for women calculation

If you're happy with a rough estimate, then, luckily for you, maths is here to help.

A study published in the British Journal of Nutrition uses the following equations to predict body fat percentages:

For women: (1.20 x BMI) + (0.23 x age) – 5.4

As such, say you were a 5ft, 4-inch 25-year-old woman who weighs 120 pounds – you would have a BMI of 20.5. You could estimate your body fat percentage to be about 25% using this calculation:

(1.2 x 20.5) + (0.23 x 25) - 5.4 = 24.95

Calipers skin-fold test

This rather old-school – and uncomfortable – method of body fat measurement involves using calipers to pinch the fat on certain areas of the body (triceps, chest, quad, waist, etc.) and measuring the skinfold.

The caliper method can be useful in identifying where you may be carrying excess body fat, as a precursor to diagnosing certain conditions. For example, the amount of fat we carry around our waist can increase our risk of serious health ailments such as heart disease, diabetes, strokes and high blood pressure.

Still, you'll need an expert to help you with this one. Even then, there's a risk of human error.

Smart scales

While they're not as cheap as your average bathroom scales, there are plenty of smart scales on the market that provide weight readings, as well as your body fat, muscle mass, water and bone density.

Prices range from about £30 upwards, and while accuracy may vary, it may be helpful to use the readings as a benchmark, if you're looking to increase or decrease body fat.

3D body scanners

Another fairly accessible option is body composition measuring machines, such as DEXA and other 3D scanners. These contraptions work using something called bioelectrical impedance analysis, the rate at which an electrical current can travel through your body. Nifty.

Unlike smart scales, these bulky, costly machines aren't exactly the kind of thing you'll buy for the corner of your bathroom. Luckily, most national gym chains, such as David Lloyd, F45 and Virgin Active will have their own available to members.

Air displacement plethysmography

We've reached the options that lab-level accuracy (and a cost). Air displacement plethysmography is a rather fancy, specialised test, involving a rather well-named machine called the BodPod.

It will require you to hang out in an egg-shaped chamber for a few minutes, where experts will determine how much air your body displaces. Several universities and research facilities in the UK, including the University of Westminster and the British College of Osteopath Medicine, have BodPods and offer assessments to the public, usually for around £40.

Hydrodensitometry

Hydro-what-now? (Try saying that five times fast.) Hydrodensitometry, or underwater weighing, is considered the gold standard in body fat measurement.

It involves being completely submerged in water, and measuring how much of the water is displaced. Some super-simplified science: bone and muscle have a greater density than water, so someone with a larger percentage of fat-free mass will actually weigh more in water. On the other hand, someone with more body fat mass will be lighter in the water.

Unfortunately, this is not something you can do at your local lido – you'll need to go to a special facility for a test like this, and it's less readily available in the UK than air displacement plethysmography.

Why is body fat percentage for women different from that for men?

On average, women have 6-11% more body fat than men. What's up with that? Well, it's probably to do with your body priming you to make babies.

The hormone oestrogen has been shown to reduce your ability to burn energy after eating – which translates to more fat being stored around the body.

What's a good body fat percentage for women?

According to The Royal College of Nursing, a healthy body fat percentage for women aged 20 to 40 is between 15% and 31%. As you get past 40, your ideal body fat percentage might get higher.

'While healthy levels are usually between 15 and 31% for women, this is really individual,' explains Dr Rebecca Robinson, a consultant in sports and exercise medicine. Also, there are more important metrics to consider. 'It's more important to have lower visceral fat (around the organs) and be physically fit, than low numbers on measurements of subcutaneous fat.'

Body fat percentage breakdown

5 to 9%

If your body is only between 5 to 9%, your body fat is dangerously low. Eight per cent is usually the fat essential for your body to work – and may severely compromise your health. If you're here, go and see your GP.

10 to 14%

This is still very low – athletes, for example tend to have this level of fat.

15 to 19%

Women who have 15 to 19% body fat tend to have an athletic build and be super physically fit.

20 to 24%

This is on the lower side, but still healthy.

25 to 31%

This is a good body fat percentage and the average percentage for a woman. Muscles are not so defined, arguably 'softer' but, by medical standards, this is not an issue.

30 to 34%

This percentage is when you're steering away from healthy and obesity. Your body may not be feeling as fit.

35 to 39%

Having a body fat percentage over 35% means you may develop diabetes and other diseases such as heart disease.

What are the dangers of high body fat percentage for women?

A high body fat percentage may put you at risk of a plethora of chronic conditions — many of which are major causes of death and disability – including:

• Heart attacks
• Strokes
• Diabetes
• Osteoarthritis
• Kidney disease

What are the dangers of low body fat percentage for women?

The risks associated with low body fat are similarly serious. Falling on the very low end of the spectrum will put you at risk of:

• Osteoporosis
• Nutritional deficiencies

Can a low body fat percentage for women cause no periods?

'When you’re focused on significantly lowering body fat, whether through following an extreme exercise regime and/or restricting calories, the body perceives you to be in a stressed state and decides this is not the time to reproduce,' says Dr Meggie Smith, a fellow in reproductive endocrinology and infertility at the University of Southern California.

'Signals from the brain to the ovaries, known as the hypothalamic-pituitary-ovarian axis, shut down.'

'The luteinising hormone [which triggers ovulation] isn’t produced and the ovary neither releases an egg nor makes oestrogen and progesterone.'

While being overweight or obese disrupts your reproductive system by producing too much oestrogen, veer towards the other extreme to a low body fat percentage and 'you essentially enter a post-menopausal state', warns Dr Smith.

This low-oestrogen state can have a knock-on effect, Dr Robinson says. 'This can have a very detrimental effect on bone health raising the risk of fracture, and also on your gut, immune system and mental health.'

How to maintain a healthy body fat percentage for women

Think about your calories

'If you’re consuming fewer than 2,000 calories and doing endurance sport, your intake is likely to be inadequate,' says registered nutritional therapist Jo Scott-Dalgleish.

Check your greens

Compare a droopy, day-before-expiry pack of asparagus with a fresh bunch from a local market. The first isn’t offering you much energy.

'It’s not only about a healthy diet, it’s about healthy food,' urges Dooley. 'Your gut microbes are important, so think about the food that your body’s bacteria eats.'

Ditch the carb-o-phobia

Don’t swerve carbs in favour of protein. 'The body’s primary aim is obtaining fuel,' says Scott-Dalgleish. 'If there is a lack of fuel (carbs), then the body will convert protein into it – thus not using protein for repairing or building.'

Scott-Dalgleish suggests consuming more starches and sugars (including fruit and veg) on heavier training days.