How to Use a Body Fat Percentage Calculator

·6-min read
Photo credit: Westend61 - Getty Images
Photo credit: Westend61 - Getty Images

Whether you're trying to trim down or training for gains, tracking your metrics is the simplest way to fast-track your goals. While keeping score of your sets, reps, miles and macros – and whatever else your FitBit is diligently monitoring – is the easiest way to tweak your approach in the gym (and the kitchen), the data drawn from a body fat percentage calculator will help you make sense of what you see in the mirror.

This is especially useful when you're trying to tighten your belt and fill out your sleeves at the same time. Your body can't build muscle out of thin air, after all. To pack on size, you need a calorie surplus. Go too big on the 'surplus', however, and you'll add a layer of blubber along with your newfound gains. By adopting a more nuanced approach, you'll be able to discern between muscle and fat as the digits on your bathroom scales start to rise.

You don't need to gun for a shrink-wrapped physique to benefit from a body fat percentage calculator – the metric is also a solid measure of your fitness. "When done accurately, body fat percentages can be really useful and good to track because it can help [you] evaluate your general health," says personal trainer Duncan Murray, co-owner of F45 Kensington Olympia and F45 Battersea Park. Before we chew the fat, let's get the basics covered...

What Is Body Fat?

While often used as a sweeping term for your spare type, body fat is more than the layer of skin concealing your abs. There are three different types of fat cells in the body – white, brown and beige – and they can be stored as essential, subcutaneous, or visceral fat. Not all body fat is inherently unhealthy. Brown fat, for example, breaks down sugar and fat molecules in your bloodstream to maintain your body temperature when you get too cold.

When tracking your stats with a body fat percentage calculator, you're measuring white fat – your body's way of stockpiling energy for later use. These large cells are stored under the skin (known as subcutaneous fat) and around the organs (known as visceral fat). Aside from shrouding your six-pack, excess white fat increases your risk of developing health conditions like type 2 diabetes, cancer, and coronary artery disease.

Your body needs a certain amount of fat to function, known as essential fat. Train your body fat percentage too low, and you risk brittle bones, tanked T-levels, and – terrifyingly – cardiac arrhythmias. Brain fog, irritability and constant hunger are frequent side effects. "When your body fat percentage is too low, your immune system can be affected and you can have low energy," Murray adds. "So it's not always about getting as low as possible."

What Is a Body Fat Percentage Calculator?

A body fat percentage calculator is a mathematical formula that deciphers what percentage of your body weight is made up of fatty tissue. A variety of methods are available, but they vary in terms of accessibility (some are only available to university medical teams) accuracy, and wallet-friendliness. The most reliable methods involve specialist teams and expensive kit like air-pressurised chambers, infrared sensors and x-ray scanners.

You needn't fork out at a dedicated facility, because we've got a body fat percentage calculator formula you can use at home. While the calculation might not be as accurate as clinical methods, it costs nothing but a few minutes of your day. It's far more effective to deploy one method frequently – using the figures as a reference point to track your progress over time – than splash out on a pricier option once every six months or so.

Photo credit: Corey Jenkins - Getty Images
Photo credit: Corey Jenkins - Getty Images

How to Calculate Body Fat Percentage

To figure out the composition of your physique using our body fat percentage calculator, below, you'll need a soft tape measure and a set of scales – ideally digital scales, if you have them. For the most accurate results, take the measurements first thing in the morning, before you've had anything to eat or drink (and prior to your workout).

After weighing yourself, whip the tape measure around your waist and measure the largest part of your belly – usually, this is around your belly button. Tempting as it might be, don't hold your breath or suck in your stomach or you'll skew the results. Once you've got those two key pieces of data, input them into the body fat percentage calculator formula:

First, you'll need to calculate your lean body weight in pounds: (1.082 x your total weight in pounds) - (4.15 x your waist measurement) + 94.42 = [x] pounds

Then, you'll convert your lean body mass to your body fat percentage: (your body weight - your lean body mass) / (your body weight in pounds) x 100 = [x] %

Looking for a simpler calculation? You can also use your body mass index (BMI) – your weight in kilograms divided by the square of height in metres – to determine your body fat percentage, but the formula will be slightly less accurate.

1.20 × your BMI + 0.23 × your age - 16.2 = [x] %

While the formulas above are, admittedly, not the most accurate body fat percentage calculator tools, they'll arm you with a rough figure that you can confirm using other methods if you choose. Alternatively, you can disregard the exact numbers and simply use the ballpark number to gauge whether your stats are going north or south over time.

What Is Ideal Body Fat Percentage?

Now you've pinned down your vital stats, it's time to see how your body fat percentage stacks up. The good news? You don't have to be shredded to be healthy. For men aged 20-39, between 8 and 20 per cent is the ideal body fat percentage range for general health; those aged 40 to 59 should aim for between 11 and 22 per cent; while men aged 60 to 79 should fall between 13 and 25 per cent.

If you're in the process of honing a washboard stomach and want a better idea of the body fat percentage that'll makes your abs pop, the American Council on Exercise (ACE) has broken down the various categories as follows:

  • Essential: 2-5%

  • Athletes: 6-13%

  • Fitness: 14-17%

  • Acceptable: 18-24%

  • Obese: >25%

It's important to recognise that whittling your number down to single (or low double) digits doesn't happen by chance. Leaving little room for a large latte – let alone a takeaway – it requires tactical planning, a disciplined approach to training and nutrition, and a diligent calorie deficit that forces your body to use stored fat for energy. It's hard work.

And while a body fat percentage calculator can be useful in quantifying your gym progress, it's not the final word for your wellbeing. If you're consistently skipping sleep to squeeze in a mammoth workout and have eaten little other than chicken and broccoli for weeks, you'll be burned out by the time you reach your coveted goal.

Use it as a tool, not a rule.

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