Mealiv
Body Fat Calculator
Estimate what proportion of your weight is fat — plus your fat mass and lean mass — using nothing more than a tape measure.
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Body fat percentage tells you something weight and BMI cannot: how much of you is fat and how much is everything else. It is particularly useful when the scales are not moving but your body is changing.
This calculator uses the US Navy circumference method, which needs your height and two or three tape measurements. It is an estimate — the sections below explain how to measure properly, and how much confidence the number deserves.
Your estimated body composition
What is body fat percentage?
Your body fat percentage is the share of your total weight made up of fat. If you weigh 80kg at 20% body fat, roughly 16kg is fat and 64kg is fat-free mass — muscle, bone, organs, water and connective tissue.
Fat is not the enemy of that equation. Your body needs a certain amount to store energy, produce and regulate hormones, insulate itself, protect organs, support cell function and absorb the fat-soluble vitamins A, D, E and K.
The aim is not the lowest possible number. It is a level that supports your health and whatever you are actually training for.
How the calculator works
It uses the US Navy circumference method, which estimates body fat from the relationship between your height and the places fat is commonly stored.
For men it uses height, neck and waist. For women it adds hip circumference, because fat distribution differs and the equation was derived separately for each.
The advantage is obvious: it needs a tape measure and nothing else. The limitation is equally real — it infers composition from shape, so it cannot see what is under the tape.
How to measure properly
Placement matters more than anything else here. A couple of centimetres in the wrong spot moves the result by several percentage points, which is enough to invent progress that has not happened or hide progress that has.
Use a flexible, non-stretch tape and the same technique every time.
Neck
Around the neck just below the larynx. Keep the tape level and let it rest on the skin without pulling.
Waist
At the level of the navel, against bare skin. Stand naturally, breathe out normally, and do not hold your stomach in. Keep the tape horizontal all the way round.
Hips
Around the widest part of the hips and buttocks, feet together, tape level.
Every time
- Measure against skin, or the lightest possible clothing
- Stand relaxed rather than braced or flexed
- Keep the tape horizontal and snug without compressing
- Take each measurement two or three times and use the average
- Measure at the same time of day, ideally morning before eating
Body fat percentage vs BMI
| Measure | What it uses | What it tells you |
|---|---|---|
| BMI | Height and weight | Weight relative to height |
| Body fat % | Measurements or composition testing | How much of your weight is fat |
| Waist circumference | Waist | Abdominal size, a proxy for visceral fat |
| Lean body mass | Weight and body fat % | Weight of everything that is not fat |
BMI is a useful screening measure but cannot distinguish fat from muscle, which is why a heavily muscled person can register as overweight with low body fat. Body fat percentage addresses that specific blind spot — while introducing measurement error of its own. Neither is a diagnosis, and the two are most useful read together.
Why bother tracking it?
Because body weight cannot tell you what changed. A stable weight can hide fat loss and muscle gain happening at the same time, and that is a good outcome reported as no outcome.
It is most useful when you are reducing body fat, running a strength programme, trying to hold muscle during weight loss, or comparing trends over months rather than days.
This is also the answer to the most demoralising situation in weight loss: the scales stuck for three weeks while the waist measurement quietly drops. One of those numbers is telling you the truth.
What is a healthy body fat percentage?
There is no single right answer. Typical levels vary with sex, age, genetics, hormonal status, muscle mass, training history and the measurement method itself.
Women carry more body fat than men at equivalent fitness, for physiological and reproductive reasons. That is normal biology, not a gap to close.
Illustrative ranges for men
| Body fat | Description |
|---|---|
| Below 6% | Exceptionally low |
| 6–13% | Athletic range |
| 14–17% | Lean / fitness range |
| 18–24% | Typical general range |
| 25% and above | Higher body-fat range |
Illustrative ranges for women
| Body fat | Description |
|---|---|
| Below 14% | Exceptionally low |
| 14–20% | Athletic range |
| 21–24% | Lean / fitness range |
| 25–31% | Typical general range |
| 32% and above | Higher body-fat range |
These are broad fitness reference ranges, not clinical thresholds. Being outside one does not mean you are unhealthy; being inside one does not mean you are well.
Can body fat be too low?
Yes, and this deserves as much attention as the other direction.
Essential body fat supports normal physiology. Very low levels are associated with low energy, poor recovery, hormonal disruption, menstrual changes including loss of periods, weakened immune function, difficulty staying warm and reduced bone density.
The extremely lean physiques visible in competitive sport are usually held briefly, for a specific event, under supervision — and not maintained year-round.
Please do not treat this calculator as encouragement to chase the lowest number you can reach. If you are experiencing persistent fatigue, missed periods, frequent injury, dizziness, or find that food, exercise or body composition occupies more of your thinking than you would like, that is worth talking to a GP about. In the UK, Beat runs a free confidential helpline.
Can body fat be too high?
Carrying a lot of body fat, particularly around the abdomen, is associated with higher risk of type 2 diabetes, cardiovascular disease, high blood pressure, fatty liver disease, sleep apnoea and some cancers.
Where fat sits matters as much as how much there is. Visceral fat around the organs is more strongly linked to metabolic risk than total body fat, which is why waist circumference adds information that a percentage does not.
Read a body fat estimate alongside your waist measurement, blood pressure, blood glucose, cholesterol and fitness — not on its own.
Fat mass and lean body mass
Fat mass
The estimated weight of fat you carry.
fat mass = body weight × body fat %
At 75kg and 24% body fat, that is 18kg of fat mass.
Lean body mass
Everything else — muscle, bone, organs, water, connective tissue.
lean body mass = body weight − fat mass
The same person would have roughly 57kg of lean mass. Note that this is not muscle mass: it includes a great deal besides. Lean mass is the number worth protecting during weight loss, and it is protected by eating enough protein and lifting something heavy twice a week.
How accurate is this?
Approximate. Circumference formulas typically land within a few percentage points of a laboratory method, and can be further out for body shapes unlike those the equation was derived from.
Accuracy depends on tape placement, consistency between sessions, your body shape, where you personally store fat, muscle distribution, and whether the formula suits you at all.
The practical consequence: treat the absolute number with suspicion and the direction with interest. A move from 28% to 24% across three months, measured the same way each time, is meaningful even if neither figure is exactly right.
Other ways to measure body fat
Smart scales
Bioelectrical impedance passes a small current through the body and infers composition from resistance. Convenient, and heavily affected by hydration, recent food, exercise and skin temperature — which is why the reading can move several percent between morning and evening.
Skinfold callipers
Measure the thickness of skinfolds at several sites. Can be good, but accuracy depends almost entirely on the skill of whoever is holding them.
DXA scan
Separates fat, lean tissue and bone mineral, region by region. The usual reference standard in research, and the most informative option generally available to the public.
Hydrostatic weighing and Bod Pod
Estimate composition from body density, via underwater weighing or air displacement. Accurate but rarely convenient.
No everyday method is free of error, including the expensive ones.
Why methods disagree
A tape measure, a smart scale and a DXA scan will give three different numbers on the same morning. That is expected: each estimates a different thing by a different route. Circumference formulas read shape, scales read electrical resistance, callipers read subcutaneous fat, DXA reads tissue attenuation.
So do not compare across methods. Pick one, use the same equipment, sites, time of day and conditions each time, and read the trend. Consistency beats accuracy for anything you intend to track.
Why the number moves day to day
Your actual body fat does not change meaningfully in a day. The estimate can, because of hydration, food and drink, bloating, recent training, tape placement, muscle tension, menstrual cycle phase and ordinary measurement error.
Measure under similar conditions, and look across several weeks. Reacting to a single reading is how people abandon plans that are working.
How to reduce body fat
Fat loss requires a sustained calorie deficit. What makes it fat loss rather than weight loss is everything around it.
A moderate deficit
Aggressive deficits cost lean tissue and are harder to sustain. The calorie deficit calculator sets a sensible starting target, and the TDEE calculator works out what you are subtracting from.
Enough protein
The single biggest lever for keeping muscle while losing fat. Work out your target with the protein calculator.
Resistance training
Gives the body a reason to keep the muscle it has rather than break it down for energy.
Daily movement
Walking and general activity contribute more to total expenditure than most people expect — often more than the training sessions.
Sleep and a balanced diet
Short sleep makes appetite and decisions harder. Meals built around protein, fibre, fruit and vegetables make the same calorie target considerably easier to live with.
Can you lose fat without losing weight?
Yes — body recomposition. Fat falls while muscle rises, so the scales barely move while your waist shrinks, your clothes fit differently, your strength improves and your estimated body fat drops.
It is most likely if you are new to resistance training, returning after a break, or carrying enough stored energy to fuel the process. It is also the clearest single argument for not judging progress by body weight alone.
Can you target fat loss from one area?
No. You can strengthen a specific muscle, but you cannot instruct your body to take fat from the area around it. Sit-ups build abdominal muscle; they do not preferentially remove abdominal fat.
Where you lose from first is governed by genetics, sex, age and hormones. Reducing total body fat will eventually reduce it everywhere — just not in the order you would choose.
Common measurement mistakes
- Pulling the tape tight. It should touch without compressing.
- Moving the site. Even a couple of centimetres changes the answer; use the same landmarks every time.
- Holding your stomach in. Breathe out normally and stand relaxed.
- Measuring over clothing. Skin, or the thinnest layer possible.
- Comparing methods. A scale and a tape will disagree; that is not an error, it is two different estimates.
- Reacting to one reading. Trends over weeks, not single mornings.
- Chasing the lowest number. Lower is not automatically healthier.
Turning the number into a plan
A body fat estimate is a starting point, not an outcome. What changes it is what you eat and how you train, repeated for months.
Mealiv sets a calorie target, builds meal plans around it, tracks protein and the rest of your nutrition as you log, turns plans into shopping lists, and shows the trend over months rather than mornings — which is the timescale body composition actually works on.
How this is calculated
Body fat percentage is estimated with the US Navy circumference method, a logarithmic equation derived from height and tape measurements. For men it uses neck and waist; for women it adds hip circumference. Fat mass is body weight multiplied by the estimated percentage, and lean body mass is the remainder. Category labels are broad fitness reference ranges rather than clinical thresholds. Circumference methods are approximations and typically differ from laboratory measurement by several percentage points.
men: 495 ÷ (1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height)) − 450
women: 495 ÷ (1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height)) − 450
Sources
Frequently asked questions
What is body fat percentage?
The proportion of your total weight made up of fat. The remainder — muscle, bone, organs, water and connective tissue — is fat-free mass.
Is body fat percentage more accurate than BMI?
It measures something different rather than something better. BMI compares weight with height; body fat percentage estimates how much of that weight is fat. Tape estimates carry their own error, so neither should be used alone.
Can I calculate body fat without weighing myself?
Yes. The percentage comes from height and circumference alone. Your weight is only needed to convert it into fat mass and lean mass.
Is body fat the same as visceral fat?
No. This estimates total fat. Visceral fat sits around the organs and is more closely linked to metabolic risk; no tape calculator measures it directly, though waist circumference is a reasonable proxy.
Why does it ask for my neck measurement?
The equation uses the relationship between neck, waist, hips and height. The neck is relatively unaffected by stored fat, so it helps the formula separate fat from frame size.
Why is hip circumference only used for women?
The female equation was derived with it, because women more commonly store a greater share of fat around the hips and thighs. The male equation does not use it, so the field is hidden rather than ignored.
Can a body fat calculator measure muscle?
No. It estimates fat percentage and, with your weight, fat-free mass — which includes muscle but also bone, organs and water.
How often should I measure?
Every two to four weeks. Daily measurement mostly captures noise.
Does muscle affect the result?
Yes. Muscle distribution and body shape affect how well a circumference equation fits, so very muscular people tend to get less reliable estimates.
Should children use this calculator?
No. Adult equations and categories are not designed for children or adolescents, whose composition changes throughout growth.
Change the number, not just measure it
Set a calorie target, plan meals that protect lean mass, and track the trend over months with Mealiv.
Start planning freeImportant information
This calculator provides a general estimate for adults and is not a medical assessment. It is not suitable for children or adolescents, during pregnancy, for people with conditions affecting fluid balance, or for diagnosing obesity or any other condition. Speak with a GP, registered dietitian or other qualified healthcare professional if you have concerns about your weight, body composition, or your relationship with food and exercise.