Body Fat Percentage Calculator — the United Kingdom
Body fat percentage from a tape measure rather than a scale — the US Navy circumference method — with the category it falls in, the healthy range for your sex, and how much of your weight is fat against lean tissue.
Weight alone cannot tell fat from muscle, which is why a lean, heavy person and an unfit, light one can share a BMI.
| max | 45 |
|---|---|
| min | 0 |
| value | 20.78 |
How the body fat calculator works
Weight alone cannot tell fat from muscle, which is why a lean, heavy person and an unfit, light one can share a BMI. The circumference method gets closer for the price of a tape measure: it reads the difference between waist and neck for men, and waist plus hip less neck for women, against height on a logarithmic scale. The logarithm is the part that matters — the same extra centimetre at the waist means much more on a small frame than a large one, and a linear formula would miss that entirely. Measure at the navel for the waist, below the larynx for the neck, and at the widest point for the hip, with the tape snug and not compressing; a centimetre of sloppiness moves the answer by roughly a point, which is larger than most of the change anyone is trying to measure. It is an estimate and it is meant to be: against a DEXA scan this method sits within about three points for most people and is worse at the extremes, so use it to watch a direction over months rather than to settle a number today.
Formula: men: 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76 · women: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387 (measurements in inches)
UK Body Fat Notes
The US Navy method
This calculator uses the US Navy circumference method, one of the most widely validated non-invasive body fat estimation techniques. It uses neck, waist, hip (women only), and height measurements with a logarithmic formula.
Male formula
BF% = 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Female formula
BF% = 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
How to measure correctly
- Waist: measure at the narrowest point (just above the belly button for most people), standing relaxed — not sucked in
- Neck: measure just below the larynx (Adam's apple), keeping the tape horizontal
- Hip (women): measure at the widest point of the hips and buttocks
- Height: stand barefoot, measure against a wall
Accuracy
The US Navy method has a typical error of ±3–4% compared to DEXA scan. It is most accurate for people with average body composition — less accurate for very muscular individuals or those with BMI over 35.
Body fat categories Body fat categories for men and womenWhat the categories mean and healthy ranges for Britons
Male body fat categories
| Category | Body fat % | Description |
|---|---|---|
| Essential fat | 2%–5% | Minimum for organ function — not sustainable |
| Athletic | 6%–13% | Lean, visible muscle definition |
| Fitness | 14%–17% | Healthy, active lifestyle |
| Average | 18%–25% | Typical UK male adult |
| Obese | 26%+ | Excess fat, increased health risk |
Female body fat categories
| Category | Body fat % | Description |
|---|---|---|
| Essential fat | 10%–13% | Minimum including reproductive fat |
| Athletic | 14%–20% | Lean, visible muscle tone |
| Fitness | 21%–24% | Healthy, active |
| Average | 25%–32% | Typical UK female adult |
| Obese | 33%+ | Excess fat, increased health risk |
Why women have more essential fat
Women naturally carry more body fat due to hormonal factors and the physiological requirements of reproduction. The essential fat threshold for women (10–13%) is much higher than men (2–5%). This is normal and healthy — very low body fat in women can disrupt hormonal function and menstrual cycles.
DEXA, callipers, BIA scales, Navy method — accuracy and cost
| Method | Accuracy | Cost | Access |
|---|---|---|---|
| US Navy (circumference) | ±3–4% | Free | Anyone — measure at home |
| Skinfold callipers (7-site) | ±3–5% | £20–£50 | Requires trained operator |
| BIA scales | ±3–8% | £30–£500 | Affected by hydration, food, time of day |
| Air displacement (Bod Pod) | ±2–3% | £50–£150 | Universities, sports institutes |
| Hydrostatic weighing | ±1–2% | £100–£200 | Specialist facilities |
| DEXA scan | ±1% | £50–£150 | Medical imaging centres |
Best approach for tracking progress
Regardless of which method you use, consistency matters more than absolute accuracy. Using the same method, same time of day, and same conditions each time gives reliable trend data even if the absolute number is slightly off. DEXA is ideal for a baseline reading; the Navy method works well for monthly tracking.
DEXA in the United Kingdom
DEXA scans measure bone density, fat mass, and lean mass throughout the body. Some clinics bulk-bill DEXA when medically indicated; otherwise expect to pay £50–£150 privately. Sports medicine clinics and universities with exercise science programs often have DEXA available at lower cost.
How to reduce body fat while preserving muscle in the United Kingdom
Calorie deficit is necessary
Body fat reduction requires a sustained calorie deficit — consuming less energy than you expend. A deficit of 500–1,000kJ per day leads to approximately 0.5–1kg of fat loss per week. This is sustainable; larger deficits increase muscle loss and metabolic adaptation.
Resistance training preserves muscle
During weight loss, a significant proportion of lost weight is muscle unless resistance training is maintained. Training with weights 2–3 times per week signals the body to preserve muscle mass. This is why a gym-based approach typically produces better body composition outcomes than diet alone.
Protein intake
Higher protein intake (1.6–2.2g per kg of bodyweight per day) during calorie restriction helps preserve lean mass. UK dietary guidelines recommend a minimum of 0.8g/kg, but this is insufficient during active fat loss. Good sources: lean meat, fish, eggs, dairy, legumes, and protein supplements if needed.
Waist circumference as a target
Rather than targeting a specific body fat percentage, reducing waist circumference to under 94cm (men) or 80cm (women) is the primary cardiometabolic health goal. Research consistently shows that reducing waist size, even without large overall weight loss, significantly reduces cardiovascular and diabetes risk.
Frequently asked Frequently asked questions
What is a healthy body fat percentage in the United Kingdom?
For UK adults, the healthy range is generally 14%–25% for men and 21%–32% for women. These ranges align with international guidelines and are associated with lowest all-cause mortality in population studies. Athletes typically fall in the 6–13% range (men) or 14–20% range (women).
Is BMI or body fat percentage more accurate?
Body fat percentage is more informative because it directly measures the proportion of fat versus lean mass. BMI cannot distinguish between fat and muscle — a muscular person may have a "overweight" BMI with healthy body fat. However, BMI is easier to measure and is used as a population screening tool. Using both together gives a fuller picture.
How accurate is the US Navy method?
The US Navy circumference method has a typical error of ±3–4% compared to DEXA scan — the gold standard. It tends to be slightly less accurate for very muscular individuals and people with BMI over 35. For tracking progress, the key is to use the same method consistently rather than comparing results from different methods.
How can I reduce body fat without losing muscle?
Combine a moderate calorie deficit with resistance training 2–3 times per week, and ensure adequate protein intake (1.6–2.2g per kg of bodyweight daily). This approach preserves lean mass while reducing fat mass. Avoid very large calorie deficits — they accelerate muscle loss and slow metabolism.
Where these figures come from
Health thresholds and UK population statistics on this page are drawn from primary authorities — the National Health Service (NHS), the National Institute for Health and Care Excellence (NICE), and the World Health Organization (WHO).
- Adult BMI formula & categories — NHS — BMI healthy weight calculator.
- WHO adult BMI categories — WHO — Obesity and overweight fact sheet.
- UK overweight & obesity statistics — NHS Digital — Statistics on Obesity, Physical Activity and Diet.
- NICE weight-management guidance — NICE — Obesity guidance.
- NHS physical-activity guidelines — NHS — Physical activity guidelines for adults.
Last checked: April 2026. Rates and thresholds are reviewed against the source of record each November, when annual adjustments for the following tax year are published.
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Male: waist 90cm, neck 38cm, height 175cm ~20.8% body fat — Average
Using the US Navy formula for males: BF% = 86.010 × log10((90−38)/2.54) − 70.041 × log10(175/2.54) + 36.76 = ~20.8%. This falls in the Average category for men (18–25%). At 80kg bodyweight: ~16.6kg fat mass, ~63.4kg lean mass.
| Body fat | ~20.8% |
|---|---|
| Category (male) | Average (18%–25%) |
| Fat mass (at 80kg) | ~16.6kg |
| Lean mass (at 80kg) | ~63.4kg |
| Athletic range target | Under 14% |
| Method | US Navy circumference method |
- To reach Fitness range (<18%) Reduce waist by ~4cm or lose ~2.7kg fat
- To reach Athletic range (<14%) Reduce waist by ~9cm
- Accuracy vs DEXA scan +/-3% typical error
- Waist health target (men) Under 94cm
- BMI at 80kg / 175cm BMI 26.1 — overweight (but BF% healthy-ish)
Female: waist 85cm, hip 95cm, neck 32cm, height 165cm ~32.7% body fat — Obese
Using the US Navy formula for females: BF% = 163.205 × log10((85+95−32)/2.54) − 97.684 × log10(165/2.54) − 78.387 = ~32.7%. This falls in the Obese category for women (32%+). At 65kg: ~21.3kg fat, ~43.7kg lean.
| Body fat | ~32.7% |
|---|---|
| Category (female) | Obese (32%+) |
| Fat mass (at 65kg) | ~21.3kg |
| Lean mass (at 65kg) | ~43.7kg |
| Fitness range target | 21%–24% |
| Method | US Navy circumference method |
- To reach Fitness range Reduce combined waist+hip by ~15cm
- Healthy range for women 25%–32% is normal/average
- Accuracy vs DEXA +/-3.5% typical error for women
- Waist health target (women) Under 80cm
- Hip measurement tip Measure at widest point of hips/buttocks
Body fat percentage categories — men and women Essential fat through Obese
Body fat percentage categories differ significantly between men and women due to hormonal differences and reproductive function. Women naturally carry more essential fat.
| Men — Essential fat | 2%–5% |
|---|---|
| Men — Athletic | 6%–13% |
| Men — Fitness | 14%–17% |
| Men — Average | 18%–25% |
| Men — Obese | 26%+ |
| Women — Essential fat | 10%–13% |
- Women — Athletic 14%–20%
- Women — Fitness 21%–24%
- Women — Average 25%–32%
- Women — Obese 33%+
- UK average (men) ~23–25%
- UK average (women) ~29–32%
US Navy method vs DEXA scan vs callipers Navy ±3%, DEXA most accurate
Body fat estimation methods vary significantly in accuracy and accessibility. The US Navy circumference method used here is simple and reasonably accurate for population screening — typical error is ±3–4%. For precise measurement, a DEXA scan is the gold standard.
| US Navy method (this calc) | ±3–4% error, free, no equipment |
|---|---|
| Skinfold callipers | ±3–5% error, trained operator needed |
| Bioelectrical impedance (BIA) | ±3–5% error, affected by hydration |
| Hydrostatic weighing | ±1–2% error, specialist facility |
| DEXA scan | ±1–2% error, gold standard |
| DEXA cost in the United Kingdom | £50–£150, typically at private clinics |
- Best for tracking progress Same method consistently over time
- DEXA locations Sports medicine clinics, some hospitals
- BIA scales accuracy Varies widely — morning fasted best
- Callipers sites 7-site Jackson-Pollock most accurate
- Navy method limitation Less accurate for very muscular/obese
Worked examples
| Inputs | Estimated Body Fat | Note |
|---|---|---|
| A man with a 90 cm waist and a 38 cm neck at 178 cm | 20.3% | the average band for a man |
| The same man five centimetres slimmer at the waist | 16.5% | five centimetres at the waist is worth almost four points |
| A woman with a 75 cm waist, 98 cm hip and 32 cm neck at 165 cm | 29.2% | the average band for a woman starts where a man is already obese |
The sources behind this calculator
- Mifflin MD et al., "A new predictive equation for resting energy expenditure in healthy individuals", Am J Clin Nutr 1990 — the BMR equation used here
- World Health Organization — Waist circumference and waist–hip ratio (2008 expert consultation) — waist-to-hip cut-offs
- Tanaka H, Monahan KD, Seals DR, "Age-predicted maximal heart rate revisited", J Am Coll Cardiol 2001 — 208 − 0.7 × age
- Nathan DM et al., "Translating the A1C assay into estimated average glucose values" (ADAG), Diabetes Care 2008 — eAG = 28.7 × A1c − 46.7
- Mosteller RD, "Simplified calculation of body-surface area", N Engl J Med 1987 — BSA = √(height × weight / 3600)
- NHS — national health guidance
Last checked: September 2026. The equations are fixed by their published papers and do not change with tax years or regulations; the thresholds quoted in verdicts name the body that set them.