Body Fat Calculator (Tape Measure Only, No Scale Needed)
A free body fat calculator. Enter your height, weight and age along with your neck and waist measurements taken with a tape measure, and it estimates your body fat percentage using the US Navy method. Results from the BMI-based Deurenberg and CUN-BAE formulas are shown alongside it, so you can see how much the estimates vary. Fat mass and lean body mass are calculated at the same time.
How to take each measurement
| Area | How to measure |
|---|---|
| Neck | Place the tape just below the larynx, sloping very slightly downwards at the back, and bring it right around. Keep your chin level and your shoulders relaxed. |
| Waist | Men measure at navel height; women measure at the narrowest part of the waist. Keep the tape parallel to the floor, breathe out, and pull only firmly enough that the tape does not dent the skin. |
| Hips | Measure around the widest part of the buttocks, keeping the tape parallel to the floor. This is only used in the female version of the US Navy formula. |
| Height and weight | Measuring under consistent conditions, such as after waking or before bathing, makes day-to-day comparison easier. Weight swings by 1–2 kg with food and fluids, so keep to the same time of day. |
Body fat percentage guide (adults)
| Rating | Men | Women |
|---|---|---|
| Low | Up to 9.9% | Up to 19.9% |
| Healthy (lower) | 10.0–14.9% | 20.0–24.9% |
| Healthy (upper) | 15.0–19.9% | 25.0–29.9% |
| Mildly overweight | 20.0–24.9% | 30.0–34.9% |
| Obese | 25.0% and up | 35.0% and up |
These bands are widely used for adults in Japan. Women need a certain amount of body fat to maintain reproductive function, so the healthy range sits roughly 10 points higher than for men. Appropriate levels vary with age and athletic background, so please treat these figures as a rough guide.
How the three formulas differ
| Formula | Inputs required | Characteristics |
|---|---|---|
| US Navy method | Height, neck, waist (plus hips for women) | Estimates from measured circumferences, so it picks up differences in body shape. It is used in the US military fitness standards and needs nothing more than a tape measure. |
| Deurenberg formula | Sex, age, height, weight | A BMI-based formula published in 1991. No tape measure is needed, but it tends to read high for people carrying a lot of muscle. |
| CUN-BAE formula | Sex, age, height, weight | Published by the University of Navarra in Spain in 2012. It includes a squared BMI term, which improves the fit in the obese range. |
What body fat percentage tells you
Body fat percentage is the share of your body weight made up of fat. Weight and BMI make no distinction between muscle and fat, so two people at the same weight can have completely different body composition. Knowing your body fat percentage lets you tell whether a diet is going to plan or whether you are losing muscle along with the fat.
You do not need a body composition scale to estimate it. This tool leads with the US Navy method, used in the US military fitness standards, and shows the BMI-based Deurenberg and CUN-BAE results next to it. Seeing how far the three figures spread stops you reading too much into any single number. Everything is calculated inside your browser, and the body measurements you enter are never sent to a server.
How to calculate your body fat percentage
- Enter sex, age, height and weight The formulas use different coefficients for men and women, so selecting your sex is required. This alone is enough to show a BMI-based estimate.
- Measure your neck and waist Run a soft tape measure around, keeping it parallel to the floor. Women should also measure the hips. Pull it snug but not tight enough to dent the skin.
- Enter the measurements The estimate switches automatically to the US Navy method, which reflects your actual proportions far better than a BMI-based figure.
- Check the rating and breakdown Along with the rating band you get your fat mass and lean body mass (LBM). When setting a weight target, aim to keep the lean body mass unchanged.
Tips for getting more out of it
- Watch the trend rather than the absolute value. Different formulas give results a few percent apart, but as long as you stick to one formula the direction of change is reliable. Measuring once a week, on the same day and at the same time, works well.
- Use a non-stretch fabric tape. A stretchy tape can vary by several centimetres depending on how hard you pull, and that alone shifts the result by 1–2%.
- For men the US Navy formula assumes the waist is measured at navel height, not at the narrowest point. Measuring at the slimmest spot will make your body fat look lower than it is.
- If you carry a lot of muscle, the BMI-based formulas (Deurenberg and CUN-BAE) will read high. Anyone who trains regularly should give more weight to the US Navy figure.
- You can feed the resulting percentage straight into our lean body mass calculator or TDEE and calorie target calculator to work out a realistic goal weight.
When a body fat calculator helps
Checking progress on a diet
If your weight drops but your body fat percentage does not move, you may be losing muscle too. Tracking fat mass in kilograms shows whether it is really only fat coming off.
Managing a bulking phase
Confirm that body fat is not climbing sharply while you gain weight. If lean body mass is rising, the extra weight is going where you intended.
Comparing against a health check
Read your body fat percentage alongside the waist and BMI figures from a medical check-up, and the areas worth working on become far more concrete.
Sanity-checking a smart scale
Impedance scales swing by several percent with hydration. Comparing against a tape-measure estimate gives you a second opinion when a reading looks odd.
Body composition terms
- Body fat percentage
- The proportion of your total body weight that is fat. It describes the balance of your body composition, which weight or appearance alone cannot show.
- US Navy method
- A way of estimating body fat from height and circumferences (neck, waist and, for women, hips). It is used in US military fitness standards and needs only a tape measure.
- BMI
- Body mass index, calculated as weight (kg) divided by height (m) squared. It is easy to work out, but because it cannot separate muscle from fat it is a poor guide to body composition.
- Lean body mass (LBM)
- Body weight minus fat mass, which is the combined weight of muscle, bone, organs and water. Preserving it is the aim during weight loss.
- Essential fat
- The minimum body fat needed to stay healthy, around 3% for men and 12% for women. Dropping below this level risks damaging your health.
- Bioelectrical impedance
- A method that passes a weak current through the body and estimates fat from the resistance. Most home body composition scales use it, but readings are affected by hydration.
- DEXA scan
- A scan using two X-ray energies to measure body composition. It is one of the most accurate methods available and is used in research and clinical settings.
Frequently asked questions
Side Note — why the US Navy built a body fat formula
The US Navy method comes from a 1984 paper by Dr Hodgdon and colleagues at the Naval Health Research Center. The motivation behind the research was far more practical than health promotion. The Navy needed to manage fitness standards across its personnel, but hydrostatic weighing, the most accurate method available at the time, required substantial equipment and could never be applied to hundreds of thousands of people.
What was needed instead was a method that any officer could carry out in a few minutes with a single tape measure, and get the same answer as the next person. The apparently odd pairing of neck and waist comes straight from that constraint. The waist stands in for the areas where fat accumulates, while the neck acts as a proxy for overall frame size. Taking the difference separates being overweight from simply being a large person.
What is striking is that four decades on, the formula has not been fully replaced by anything newer. On accuracy alone it is nowhere near a DEXA scan, but very few methods manage to be equipment-free, consistent between different people taking the measurements, and calculable on the spot, all at once. Even in an age of household smart scales, it remains worth consulting as an independent estimate that hydration cannot skew.
Body fat percentage itself is a relatively recent idea, only becoming a common measure in the second half of the twentieth century. Before that, obesity was discussed purely in terms of height and weight. The ancestor of BMI was devised in the 1830s by the Belgian statistician Adolphe Quetelet, who created it not to assess an individual but to describe how physique was distributed across a population. It took more than a century for it to find its way into personal health checks.