Estimate body fat percentage, fat mass, lean mass, BMI, waist-to-height ratio, and target weight using body measurements.
Tip: Take all tape measurements relaxed, standing upright, and without pulling the tape too tight. Small tape errors can change body fat estimates by several percentage points.
Tip: In the UK, waist-to-height ratio is often used alongside BMI. A waist less than half your height is a simple benchmark worth tracking over time.
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| Target Body Fat | Projected Weight | Change from Current |
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Body Fat Calculator tools help you estimate how much of your body weight is fat mass versus lean mass. This calculator goes beyond a simple percentage by combining a circumference-based body fat estimate with BMI, waist-to-height ratio, lean mass, and target-weight projections so US and UK users can get a more practical picture of body composition.
Unlike a basic scale reading, this tool can show why two people with the same body weight may have very different health or fitness profiles. That matters whether you are tracking a cut, monitoring health risk, or simply trying to understand your measurements better.
The estimates here are based primarily on the U.S. Navy circumference method, which estimates body fat using height together with neck and waist measurements, plus hip circumference for women. The calculator then converts that estimate into fat mass and lean mass. It also calculates BMI using the same core approach used by the CDC and the NHS.
Because body fat percentage does not have a single universal government chart for all civilians, this tool adds context that official public-health bodies do use regularly: BMI and waist-based risk screening. The NHS also highlights waist-to-height ratio and advises that your waist should usually be less than half your height, which is why that metric is included here as well through the NHS waist-to-height guidance.
Important: circumference formulas are estimates, not a lab measurement. Hydration, tape position, muscle mass, and measurement technique can all move the result. For the best trend tracking, measure under the same conditions every time.
Interpreting body fat is broadly similar in the US and UK, but the language around healthy weight often differs. In the United States, people commonly compare body fat with BMI categories used by CDC guidance, where adult BMI under 18.5 is underweight, 18.5 to 24.9 is healthy weight, 25 to 29.9 is overweight, and 30 or more is obesity. In the UK, NHS guidance uses the same adult BMI bands for most adults, but UK health messaging often places stronger everyday emphasis on waist size and waist-to-height ratio as practical screening checks.
Another key difference is units. US users usually think in pounds, feet, inches, and waist measurements in inches. UK users often prefer kilograms and centimetres, but many still use stone and pounds in day-to-day conversation. That is why this calculator supports imperial entry for the US panel and both metric and imperial entry for the UK panel.
For muscular adults in places such as Texas, California, Florida, London, Manchester, Birmingham, Glasgow, or Cardiff, body fat percentage can be more informative than BMI alone. A strength athlete may have a BMI in the βoverweightβ range while still carrying moderate body fat. That is exactly the situation where a body fat estimate can add value.
Results are often interpreted using practical adult fitness ranges rather than one single government civilian chart. A useful reference framework is below. These are broad adult guide ranges and should be interpreted with age, training status, ethnicity, and medical context in mind.
| Category | Men | Women |
|---|---|---|
| Essential fat | 2β5% | 10β13% |
| Athletic | 6β13% | 14β20% |
| Fitness | 14β17% | 21β24% |
| Average | 18β24% | 25β31% |
| High / obesity risk range | 25%+ | 32%+ |
These ranges are not a diagnosis. For public-health screening in both the US and UK, BMI and waist-based measures still matter. If your body fat estimate is moderate but your waist-to-height ratio is high, central fat distribution may still deserve attention.
To use the calculator properly, first choose your country mode. Then enter your sex and adult age. Next, enter body weight and height in the units shown. After that, measure your neck and waist carefully with a flexible tape; women should also enter hip circumference. Finally, choose a target body fat percentage if you want a projected target weight. The results update live as you type, so you can test how different measurements or goals affect the estimate.
For better accuracy, follow a simple routine. First, measure at roughly the same time of day. Second, stay relaxed and do not suck in your stomach. Third, keep the tape level around the body. Fourth, use the same waist location every time. Fifth, look at the trend over several weeks instead of reacting to one reading.
Your body composition usually improves when you focus on preserving lean mass while reducing excess fat. In practice, that means a moderate calorie deficit, high-protein meals, resistance training, daily walking, and enough sleep. Many US users benefit from tracking both scale weight and waist size, especially if they live in high-car lifestyles where daily movement can be low.
In the UK, progress often pairs well with NHS-style healthy-weight guidance: maintain regular activity, use waist-to-height ratio as a simple checkpoint, and avoid chasing scale weight alone. If your waist is more than half your height, improving abdominal fat distribution may matter even before major scale changes appear. Walking, structured resistance training, and consistent food intake are often more useful than crash dieting.
For both countries, the best strategy is usually slow and sustainable. Rapid weight loss can reduce lean mass. If your target body fat is aggressive, aim for a gradual approach and revisit your measurements every two to four weeks.
If you want a fuller body-composition picture, try our BMI Calculator, Calorie Calculator, BMR Calculator, Ideal Weight Calculator, Lean Body Mass Calculator, Waist to Height Ratio Calculator, Healthy Weight Calculator, and Body Surface Area Calculator.
This tool gives a useful estimate, especially for trend tracking, but it is not as precise as DEXA, hydrostatic weighing, or some medical body-composition scans. Tape placement, posture, hydration, and muscularity can all affect the result.
A healthy range depends on sex, age, and activity level. Broadly, men often fall into lower percentage ranges than women because women require more essential fat. Use the result with BMI, waist-to-height ratio, training history, and medical context rather than treating one number as perfect.
BMI measures weight relative to height, not body composition. A muscular person can have a higher BMI with a moderate body fat percentage. That is why this tool shows both values together.
They answer different questions. Body fat percentage estimates overall fatness, while waist-to-height ratio highlights abdominal fat distribution. Many adults should pay attention to both, especially when waist size is rising faster than body weight.
This adult tool is not designed for children or teenagers. Younger people should use age-specific clinical tools and should discuss concerns with a qualified healthcare professional.
Every two to four weeks is usually enough. Day-to-day checking is often too noisy because measurements change with hydration, training, digestion, and tape placement.
This tool is for informational and estimation purposes only. It is not a substitute for professional medical, fitness, nutritional, or diagnostic advice. Body fat percentage formulas, BMI, waist-to-height ratio, and projected goal weights can vary based on body type, age, ethnicity, measurement technique, and individual circumstances. Review official guidance from the NHS or the CDC, and always consult a qualified healthcare professional before making health decisions.
freeusukcalculator.com
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The US Navy body fat formula uses neck, waist, and (for women) hip circumference plus height to estimate body fat percentage within 3β4% of DEXA-scan accuracy. Men: BF% = 86.010 Γ log10(waist β neck) β 70.041 Γ log10(height) + 36.76. Women: BF% = 163.205 Γ log10(waist + hip β neck) β 97.684 Γ log10(height) β 78.387. Used by US military for fitness standards; works for most adults without expensive equipment.
ACE Fitness reference ranges: Essential fat 2β5% men / 10β13% women; Athletes 6β13% men / 14β20% women; Fitness 14β17% men / 21β24% women; Average 18β24% men / 25β31% women; Obese 25%+ men / 32%+ women. Women carry essential fat for reproductive function β sub-10% body fat is unsustainable for women and typically triggers amenorrhea.
BMI uses only height + weight and cannot distinguish muscle from fat. A lean athlete with a BMI of 27 (classified "overweight") may have 12% body fat (excellent health). A sedentary office worker with a BMI of 24 ("healthy") may have 30%+ body fat (skinny-fat). Body fat percentage is consistently more predictive of cardiometabolic risk than BMI for individuals.
Protocol: TDEE β 300 to 500 calorie deficit + 0.8β1g protein per lb body weight + 3β4 resistance training sessions per week. This combination produces ~80% fat loss / 20% muscle loss vs the 50/50 ratio of pure calorie restriction without training. Expect 0.5β1% body fat reduction per month sustainably; faster rates increase muscle loss.
DEXA scan ($75β150): gold standard, Β±1% accuracy. Hydrostatic weighing: clinical-grade, Β±2%. US Navy tape method (free): Β±3β4%. Skinfold calipers (with training): Β±3β5%. Bioelectrical impedance scale ($30): Β±5β8%, hydration-sensitive. The Navy tape method gives the best free at-home accuracy and is what we use in this calculator.
The US Navy formula uses neck, waist (and hip for women) circumference plus height. Accurate within 3β4% of DEXA scans.
Men: 14β17% (fitness), 18β24% (average). Women: 21β24% (fitness), 25β31% (average). Below essential fat (2% men, 10% women) is dangerous.
Body fat percentage is more predictive of cardiometabolic health for individuals. BMI is faster to measure but unreliable for muscular or skinny-fat people.
0.5β1% body fat per month is sustainable with calorie deficit + resistance training + adequate protein. Faster rates lose muscle.
Within 3β4% of DEXA scan accuracy β better than most home scales using bioelectrical impedance.