Body Fat Percentage Calculator
Estimate body fat and lean mass without guessing every week
Body fat percentage, categories and lean mass FAQ
What does this body fat calculator actually estimate?
It estimates your body fat percentage from either circumference measurements (waist, neck, hips) or a sum of three skinfolds. It then shows your estimated lean body mass and which broad category band your % falls into for your sex.
Which method should I pick: tape or calipers?
Choose the method you can perform most consistently. Tape is easier to repeat at home if you measure in the same spots each time. Calipers can be more sensitive to changes if you’re comfortable using them and have some practice with skinfold technique.
How accurate are these body fat formulas?
Even with careful technique, circumference and skinfold equations can be off by several percentage points for an individual. They’re best for following trends over time rather than chasing an exact number. Lab methods like DEXA or underwater weighing are more precise but harder to access.
What do the category labels (athlete, fitness, average, obese) mean?
Those labels come from population-based charts that try to group typical ranges for men and women. They’re a rough guide to relative adiposity, not a measure of your worth, health or ability. Blood pressure, blood sugar, performance, sleep and mental health often matter more than a single body fat %.
Can high muscle mass make these numbers misleading?
Yes. Very muscular people can have circumference or skinfold readings that do not line up perfectly with imaging results. In those cases, trends in performance, strength, waist size, and DEXA or other scans (if available) give a clearer picture than any one home equation.
Is lower body fat always better?
Not necessarily. Very low body fat can disrupt hormones, recovery and mood, especially in women. For many people, a moderate, sustainable range with good fitness, sleep and lab markers is healthier than pushing to the leanest look possible.
Who should be especially cautious with body fat goals?
Anyone with a history of disordered eating, RED-S/relative energy deficiency, chronic illness, pregnancy, or complex endocrine issues should focus on medical advice first. In those cases, body-fat numbers can be more triggering than helpful without clinical support.
How often should I re-check my body fat?
Many people track every few weeks or once a month. Checking daily can add noise and stress. Use the same method, same tape or calipers, and similar conditions (time of day, hydration) so you’re really comparing like with like.
How to use this body fat calculator for clearer tracking
This tool is built to turn your regular measurements into an estimated body fat percentage, a simple category label and an approximate lean mass. That way you can see whether changes on the scale are more likely fat, muscle, or a mix, instead of guessing every time weight moves.
1. Pick units, sex and method
Start by choosing US or metric units, then select your sex. Decide whether you’ll track with tape (circumference) or calipers (skinfolds). Try to stick to the same method long term so your numbers are comparable.
2. Enter current height and weight
Use your current height and morning weight, not a target weight. Height can change slightly with age or spinal issues, so if it’s been years since you measured, it’s worth re-checking. These values are used to interpret the body fat % and calculate lean mass.
3. Add tape or caliper readings
For tape:
- Measure waist at the belly button.
- Measure neck just below the Adam’s apple.
- Women also measure hips around the widest part.
For calipers, enter the sum of three skinfolds in millimetres. Pick a standard trio (for example chest, abdomen, thigh for men; triceps, thigh, suprailiac for women) and be consistent about sites.
4. Read the percentage, band and lean mass
Tap Estimate body fat and lean mass to see:
- Your estimated body fat % to one decimal place.
- A category band such as essential, athlete, fitness, average or obesity for your sex.
- Approximate lean body mass and fat mass based on your weight.
You can use Copy summary to save this in a note, training log or check-in form.
5. Focus on trends, not single readings
Day-to-day numbers can bounce around from hydration, sodium and measurement error. Look at longer trends: Is waist shrinking? Is strength stable or improving? Are you feeling better in day-to-day life? Use the calculator as one reference point alongside those bigger signals.
If you are planning big body composition changes or have health concerns, pair these estimates with regular check-ins from your healthcare team rather than making large diet or training shifts alone.
How the body fat and lean mass math works
Under the hood, the calculator uses two common approaches: a circumference-based US Navy-style equation for tape inputs and a 3-site Jackson–Pollock formula for caliper sums, then converts the result into lean and fat mass.
1. Convert units where needed
In US mode, you enter height and girths in inches and weight in pounds. In metric mode, centimetres and kilograms are converted to inches and pounds or to metric-only forms before applying the formulas, so the equations still work as intended.
2. Tape method (US Navy-style circumference)
A typical male equation (in inches) is similar to:
% body fat ≈ 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
For women, hips are included and constants differ. These equations estimate body fat from ratios of girths to height using base-10 logarithms.
3. Caliper method (Jackson–Pollock 3-site)
With calipers, the tool takes the sum of three skinfolds in millimetres and your age. For men, one common 3-site equation is:
Body density = 1.10938 − 0.0008267 × sum + 0.0000016 × sum² − 0.0002574 × age
For women, coefficients differ but follow the same pattern. Body fat % is then estimated from body density using a standard conversion:
% body fat ≈ 495 ÷ density − 450
4. From body fat % to lean mass
Once body fat % is estimated, lean body mass is calculated simply as:
Lean mass = body weight × (1 − body fat % ÷ 100)
Fat mass is the difference between total weight and lean mass. These values are rounded for readability so you can compare check-ins without a spreadsheet.
Because all of these steps rely on equations and measurements with built-in noise, treat the output as a rough guide. If you need a more precise or clinically relevant picture, ask your healthcare team which testing method they recommend for you.
References and further reading on body fat estimation
These sources explain the tape and caliper methods and show where the category bands come from:
- LibreTexts — The U.S. Navy body fat estimation formula — describes a circumference-based method for estimating adult body fat % from neck, waist, hips and height.
- Topend Sports — Jackson–Pollock skinfold formulas — shows 3-, 4- and 7-site equations and how body density is converted to body fat % for men and women.
- ACE Body Composition Percentage Chart — lists common body fat % category bands (essential, athlete, fitness, average, obese) for men and women.
Use these as background reading and combine them with individual advice if you’re making health or performance decisions based on body composition.