Body composition calculators
Height, weight, a tape measure, and a set of calipers cover almost everything on this page. Each of these 14 calculators answers a different question about the same body, and none of them is the whole picture alone.
Body composition is the split between the mass on you that is fat and the mass that is not. Scale weight blends the two together, which is why two people at the same weight can look and move completely differently. The 14 calculators here pull that one number apart from several angles.
They sit together because they share inputs. Once you have your height, your weight, and a tape measure, most of them take about thirty seconds, and what you type into one carries across to the next so you are not re-entering your waist measurement five times in a row.
Every formula on these pages is a published one, and each result names the formula it used so you can go and read the source. None of these is a body scan. They are estimates fitted to large groups of people, which makes them far more useful watched over months than read once.
Where most people should begin
If you have never measured any of this before, these three in this order will tell you most of what the rest of the page refines.
- 01
BMI Calculator
The fastest one. Height and weight, nothing else, and it puts your weight in a band. It cannot tell muscle from fat, which is exactly why the rest of this page exists.
Open the calculator - 02
Body Fat Estimator
A tape measure and three minutes. The Navy method is the one most people can genuinely repeat at home, and repeatability beats precision when you are tracking a change.
Open the calculator - 03
Lean Body Mass
The number worth protecting while you diet. It splits your scale weight into fat mass and everything else.
Open the calculator
Every body composition calculator
All of them are free, none of them needs an account, and what you enter in one carries across to the next.
14 in this category
What these numbers are good for
A direction, not a verdict
The useful output is which way the number is moving and how fast. A single reading on a single morning is the least informative way to use any of these.
Something you can repeat
Same tape, same spot, same time of day, ideally before you eat. A method you repeat the same way every month will show you a real change long before a more accurate method used once ever could.
Inputs for the rest of the site
Lean mass feeds the protein target. Body fat feeds FFMI and the recomp planner. Getting these first makes every nutrition and training number downstream better.
What they cannot do
Every calculator here is a general fitness estimate rather than medical advice, and the things below are worth knowing before you act on one.
They are estimates
A tape measure and a formula will not match a DEXA scan. Two methods on the same body on the same day can differ by several percent, which is fine as long as you keep using the same one.
They are not a health assessment
These are general fitness numbers. They do not diagnose anything, and no result here should be read as a verdict on your health. If a number worries you, someone who has your history in front of them is the right next stop, not another calculator.
Muscle and frame break the simple ones
BMI and the weight tables treat every pound the same. If you carry a lot of muscle they will read high, and if you carry very little they can read reassuringly low. That is a known limit of the formula, not a fault in you.
Answered here, not behind a signup
- Which body fat calculator is the most accurate?
- Of the methods here, caliper skin folds done properly beat the tape measure methods, and the Navy tape method beats anything based on height and weight alone. The bigger factor is consistency. Pick one, use it the same way every time, and read the trend rather than the single figure.
- Is BMI useless if I lift weights?
- Not useless, but it is the wrong tool for you. BMI has no way to tell muscle from fat, so a lifter often lands a band or two higher than their body composition suggests. Use the body fat estimator and FFMI instead, and keep BMI as the thirty second version you check once a year.
- How often should I remeasure?
- Once a month is plenty for body composition. These methods carry enough noise that a weekly measurement mostly shows you hydration and measurement error rather than a real change in your body.
- What is a good FFMI?
- FFMI expresses your lean mass relative to your height, so it does not punish being tall or short the way raw lean mass does. The calculator shows where your figure sits against published ranges and explains what the bands mean. It is a way to track your own progress, not a score to compare with someone else.
The other categories
- Nutrition calculators23Maintenance calories, macro splits, protein targets, and the intake numbers that sit on top of them.
- Training calculators28One rep max, splits, RPE, progression, warm ups, and the cardio zones, plus a plain English glossary.
- Wellness and recovery calculators12Sleep timing, stress and recovery checks, hydration, steps, and the unit converter everything else needs.
Not sure which number you need?
The full index has every calculator on the site with a search box, and the guided flows walk you through a set of them in order when one number on its own is not the answer.