Health & Fitness
Body fat and FFMI
Body fat is the number everyone asks for and the less useful of the two. FFMI is the one worth knowing: how much muscle you carry for your height, and roughly how much of it is still available. A tape measure gets you both, to about the precision a tape measure deserves.
Measurements
Measure first thing, before eating, tape snug but not pulling into the skin. Take each one twice and use the average.
At the navel, relaxed, not sucked in.
Just below the larynx, sloping slightly down at the front.
FFMI, normalised
20.9
Likely 20 to 21.8
Lean mass
67.8kg
Everything that is not fat
Body fat
15.3%
Likely 11.8% to 18.8%
Where that sits
Well trained
Several years of consistent lifting and eating enough. Progress from here is measured in years rather than months.
Your raw FFMI is 20.9, and normalised to a 1.8 m frame it is 20.9. Normalising is what makes the number comparable between people of different heights, and it is the version the research is quoted against. Plenty of calculators skip it and quietly flatter shorter lifters.
Both numbers inherit the error on the body fat estimate, which is why they are shown as bands. Chasing a change of half a point month to month is chasing noise; a change of two points over a year is real.
| Method | Typical error | Worth knowing |
|---|---|---|
| DEXA scan | 1 to 2 points | The reference standard. Worth doing once if you want a real baseline. |
| Tape measure (US Navy) | 3 to 4 points | What this page uses. Free, repeatable, and good enough to track a direction over months. |
| Bathroom scale (bioimpedance) | 5 to 10 points | Moves with how hydrated you are. Useful for trends, close to useless for a single reading. |
Take this to the calorie page
Now that you have a measured body fat figure, the TDEE calculator will switch from Mifflin-St Jeor to Katch-McArdle, which works off lean mass and handles lean or heavily muscled people better. Enter 15.3% there.
If food or your body is taking up too much space
Tracking calories helps some people and hurts others. If counting is making you anxious, if you are eating less than these numbers say, or if you find yourself thinking about food most of the day, that is worth talking to someone about. Beat is the UK's eating disorder charity and their helpline is free and confidential on 0808 801 0677.
Get support from Beat