January 16

The Ideal Body Fat %, and How To Calculate It


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If there was only one number to track which would dictate how good you’ll look naked, it’s your body fat %. An ideal body fat % calculation takes into account your muscle weight, your bone weight, organ weight, fat weight, hydration status and a whole host of other things.

Your total bodyweight is certainly important, but all things being equal, a lower body fat % means you look better, and are healthier (to a certain limit – more on that shortly). Essentially, when testing body fat %, what you’re trying to do is identify lean body mass versus fat mass – that is the amount of weight in kg of your total bodyweight that is fat.

Smelly, stinky, jiggly, useless fat.

There’s a number of ways of doing it – there’s scales you stand on, measuring tape methods around your neck and belly button (that’s the US Navy Method), you can use calipers to pinch different parts of your body, or you can do expensive lab tests where they x-ray you or put you into a hydrostatic weighing chamber (…they submerge you underwater!).

Each method has varying degrees of accuracy. Some are consistent but not acccurate, and others just throw out mad numbers at random.


The weighing scales you stand on are the least accurate because they use a method called bioimpedance analysis and can be skewed plus or minus up to 5% depending on how much water you’ve drank, or whether you’ve been to the bathroom recently. If you’ve used em before – please disregard the number that came out. It’s largely meaningless.


The US Navy Tape method is a solid option that you can perform yourself at home fully clothed. It’s consistent and reliable, and since one of they key measurement is stomach size, it fits the goals of most people. BUT if you’re susceptible to bloated stomachs, it may not be the best option for you.

You can find more info and a calculator on it here: http://fitness.bizcalcs.com/Calculator.asp?Calc=Body-Fat-Navy


Last time I checked, there was about 5 different types of caliper tests personal trainers are using. For simplicity and reliability, we use the Durnin and Womersley method. It requires just 4 sites, your bicep, tricep, under your shoulder blade, and across the top of your hip.

The skin and fat are gently pulled away from the muscle at each of those sites, and a calipers is place on that spot to ascertain the amount of fat in the area. The calipers gives a reading in millimeters. The 4 sites are then combined and put into a calculator to give a bodyfat percentage. You can see a video of the process going down here: https://www.youtube.com/watch?v=VBJuVfiKrbY

It’s a painless process that only takes about 60 seconds. You can see photos of the sites here:

Good bodyfat calipers, in tandem with a good trainer, delivers reliable, consistent measurements that give a great idea of how your progressing on a diet (it’s also very useful to know how much of your weight gain is muscle versus fat, if bulking up is the goal).


The most accurate method of ideal body fat % testing is to get it done in a lab in either a bod pod, or with a DEXA scan. Most universities offer these services, but the cost can be quite high – €65-120+. For most “normal” people it’s completely unnecessary as the difference between a skilled trainer with calipers and lab testing is usually < 1%.

Before I say anything else – I want to clear up something that I see at least once a week, which makes me want to scream – you will never ever ever ever be 0% bodyfat. Unless you’re a decaying corpse. Fat in your body is an essential component of every single cell and nerve structure. Without it, you’d be dead.

The lowest “true” body fat number someone will ever see is approximately 4-5%, and that’s ONLY for male bodybuilders on stage at a show. Even female competitors won’t get lower than 10-12%.

When you see sports people or swimwear models with their kit off and their abs popping, their body fat is in the 6-10% range for guys, and 12-16% range for ladies. Cristiano Ronaldo is about 10% body fat, for example.

For most guys, the ideal body fat % range is 13-15%. 19-21% for ladies. At that level of body fat you’ll really start to look like you train with weights and have a good body. Going lower is of course, ok, but typically requires a bigger sacrifice than getting to the aforementioned ranges.

How long it will take to get there, depends on where you’re at now – a good target is to lose approx. 0.75% body fat per week. Any higher and you’re probably not eating enough to sustain energy levels, which means it’s only going to be regained down the road. Any less and it’s happening slower than it otherwise could be.

I should note – you won’t always see a consistent drop on the scales or calipers. Sometimes it will take 2 or 3 weeks for it to happen, only for it to go “whoosh” overnight as if magic has just happened. 0.75% per week on average, over the course of 6-12 weeks is about right.


We recommend you get your body fat tested with us every 10-14 days. If you’re training with us right now, all you have to do is let us know that you want to get it tested, we’ll grab you for 5 minutes before the start of your next session and do it there and then.

Afterwards, you’ll be emailed a report with your site specific readings, the total amount of muscle versus fat you have, and an accurate timeline as to how long it will take to get down into ideal body fat % range.

Body fat calculation is a simple complicated topic. The general premise is straight forward – let’s track those numbers and get them down. Today, I just wanted you to know what goes on in the background 🙂

Any Qs – holla.

PS – This is just one of the things we cover with you during our 2 week personal training trial at RevFit. You can book your space today and get access to 2 weeks of training with us without making a long term commitment here: https://revolutionfitness.ie/trial/


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