Body Fat Percentage Calculator
Estimate body fat percentage from tape measurements using UK-friendly metric or imperial units, with clear limits on what the result can and cannot tell you.
Calculate estimated body fat percentage
Choose a formula estimate, enter your tape measurements, and get an approximate body fat result.
What body fat percentage means
Body fat percentage estimates how much of your body weight is made up of fat mass rather than lean mass such as muscle, bone, organs and water.
It can be more informative than BMI for some people because two people with the same weight and height can have different body composition. Even so, a tape-measure calculator is still only an estimate.
How to take the measurements
- Height: stand upright and use your height without shoes.
- Waist: measure around your waist with the tape level and snug, not pulled tight.
- Neck: measure around the neck at a consistent point each time.
- Hips: for the female estimate, measure around the widest part of the hips.
Consistency matters more than chasing a perfect single reading. If you are tracking change, repeat the same method each time.
Body fat percentage formula
The calculator uses a circumference-based formula. Metric measurements are converted internally before the equation is applied.
Male estimate:
body fat % = 86.010 × log10(waist − neck)
− 70.041 × log10(height)
+ 36.76
Female estimate:
body fat % = 163.205 × log10(waist + hips − neck)
− 97.684 × log10(height)
− 78.387The result should be treated as a broad estimate. It can be useful for tracking trends, but it is not a medical diagnosis or a complete health assessment.
When this estimate can be misleading
The formula can be affected by measurement technique, body shape, water retention, muscle mass, age, sex and where you hold body fat. It also cannot tell you about blood pressure, cholesterol, fitness, diet quality or overall health.
For a broader picture, compare this with the BMI Calculator, Ideal Weight Calculator and your own health context.
Worked examples
What to do with the result
Use the number as a tracking estimate, not a judgement. If your goal is weight management, you may also want to estimate your daily calories, protein needs and a sensible training or activity plan.
FAQs
Is body fat percentage better than BMI?
It can add useful context because it estimates body composition, while BMI only compares weight with height. But a tape-measure body fat estimate is still rough, so neither number should be used alone.
Do I need a hip measurement?
The female circumference estimate uses a hip measurement. The male estimate uses height, waist and neck only.
Why did my result change after a small measurement difference?
The formula is sensitive to tape measurements. A slightly different waist, neck or hip reading can change the percentage, which is why consistent measuring matters.
Can this calculator tell me if I am healthy?
No. It estimates body fat percentage only. Health depends on many factors, including medical history, activity, diet, sleep, blood pressure and other measurements.
Related glossary terms
Sources and assumptions
This calculator uses a common circumference-based body fat estimate and converts metric inputs internally. Results are rounded and should be treated as approximate.
For medical concerns, eating-disorder concerns, pregnancy, growth, illness or major weight change, use professional advice rather than a web calculator result.
Compare this with other health calculators
Body fat percentage is only one estimate. Compare it with BMI, calories, protein and ideal weight for a broader picture.
Calculatorz results are estimates only and are not medical advice.