BMI & Body Fat Calculator – Check Your Body Composition
Enter your height, weight, and a few measurements below to estimate your BMI and body fat percentage in seconds.
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Calculate Your BMI & Body Fat %
Enter your details to estimate your body mass index and body fat percentage.
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Fill in the form and select Calculate My Results to see your BMI and body fat percentage.
Your Body Composition Estimate
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Body Mass Index — an estimate of whether your weight is in a typical range for your height.
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Estimated body fat percentage (U.S. Navy circumference method).
These figures are estimates from standard formulas, not a medical diagnosis or individualized advice. See the health disclaimer below.
What Is BMI?
BMI (Body Mass Index) is a simple calculation that estimates whether your weight is in a typical range for your height. It's calculated by dividing your weight in kilograms by the square of your height in meters.
BMI = weight (kg) ÷ height (m)²
BMI does not distinguish between muscle and fat, and can be less accurate for very muscular people, older adults, and some other groups. It's a useful starting screening tool, not a diagnostic measurement.
BMI Categories
Adult BMI is generally grouped into four categories, based on the World Health Organization's standard ranges.
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
These ranges are general population guidelines and may not apply the same way to athletes, older adults, or people with high muscle mass.
What Is Body Fat Percentage?
Body fat percentage is the proportion of your total body weight that is made up of fat, as opposed to muscle, bone, organs, and other lean tissue. Unlike BMI, it directly estimates body composition rather than just weight relative to height.
This calculator estimates body fat percentage using the U.S. Navy circumference method, which uses your neck, waist, and (for women) hip measurements along with your height.
Body Fat Percentage Categories
Typical body fat ranges differ by sex, based on commonly used fitness-industry classifications (ACE).
| Category | Men |
|---|---|
| Essential Fat | 2 – 5% |
| Athletes | 6 – 13% |
| Fitness | 14 – 17% |
| Average | 18 – 24% |
| Obese | 25% and above |
| Category | Women |
|---|---|
| Essential Fat | 10 – 13% |
| Athletes | 14 – 20% |
| Fitness | 21 – 24% |
| Average | 25 – 31% |
| Obese | 32% and above |
How Is Body Fat Percentage Calculated?
This calculator uses the U.S. Navy circumference method, which estimates body fat from a small number of tape-measurements rather than requiring specialized equipment.
Men
%BF = 495 / (1.0324
− 0.19077 × log10(waist − neck)
+ 0.15456 × log10(height)) − 450
Women
%BF = 495 / (1.29579
− 0.35004 × log10(waist + hip − neck)
+ 0.22100 × log10(height)) − 450
All measurements are in centimeters. This method is a field estimate — it is less accurate than clinical methods like DEXA scans or hydrostatic weighing, and is sensitive to measurement technique.
How to Measure Your Neck, Waist, and Hip Correctly
Accurate measurements make a real difference to the result — a loose or crooked tape can shift the estimate by several percentage points.
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Neck
Measure just below the larynx (Adam's apple), with the tape sloping slightly downward toward the front.
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Waist
Measure at the narrowest point of your torso, usually just above the belly button, without pulling the tape tight.
-
Hip (for women)
Measure around the widest part of your hips and buttocks, keeping the tape level and parallel to the floor.
Take each measurement two or three times and use the average for a more consistent result.
BMI vs Body Fat Percentage: What's the Difference?
BMI looks only at weight relative to height, while body fat percentage estimates what proportion of that weight is actually fat.
| Metric | BMI | Body Fat % |
|---|---|---|
| Meaning | Weight relative to height | Proportion of body weight that is fat |
| Accounts for muscle? | No | Yes, indirectly |
| Inputs needed | Height and weight | Height plus neck/waist/hip measurements |
| Best for | Quick population-level screening | A closer look at body composition |
What Affects Body Fat Percentage?
Genetics
Where and how easily your body stores fat is partly inherited.
Age
Body composition tends to shift toward more fat and less muscle with age.
Sex
Essential fat levels differ between men and women.
Diet
Long-term calorie balance strongly influences body fat levels.
Exercise Type
Resistance training and cardio affect muscle and fat differently.
Hormones
Hormonal changes can shift fat storage and distribution.
Muscle Mass
More muscle generally means a lower body fat percentage at the same weight.
Sleep
Poor sleep is associated with changes in appetite and fat storage.
Stress
Chronic stress can influence eating patterns and fat distribution.
Hydration
Short-term hydration changes can slightly affect measurement-based estimates.
BMI & Body Fat Questions, Answered
What does BMI stand for?
BMI stands for Body Mass Index, a measure of weight relative to height.
What is a healthy BMI?
A BMI between 18.5 and 24.9 is generally classified as a normal weight range, though this can vary for athletes and other groups.
How do I calculate my BMI?
Divide your weight in kilograms by your height in meters squared, or use the calculator above.
Is BMI accurate for everyone?
No. BMI doesn't distinguish muscle from fat, so it can misclassify very muscular people or underestimate body fat in others.
What is a good body fat percentage?
This depends on sex and goals — typical "fitness" ranges are roughly 14–17% for men and 21–24% for women.
How is body fat percentage measured?
Methods range from simple circumference-based formulas (like this calculator) to skinfold calipers, bioelectrical impedance scales, and clinical methods like DEXA scans.
Is the U.S. Navy method accurate?
It's a reasonable field estimate for most people, but less precise than clinical methods, and sensitive to measurement technique.
Can BMI and body fat percentage disagree?
Yes. A muscular person can have a high BMI but a low body fat percentage, and vice versa.
Does body fat percentage change with weight loss?
Yes, though the relationship depends on whether the weight lost is mostly fat or includes muscle.
Should I track BMI or body fat percentage?
Many people find body fat percentage more informative for body composition goals, while BMI remains a quick general screening number.
Frequently Asked Questions
It estimates your BMI and your body fat percentage using the U.S. Navy circumference method, from a few basic measurements.
Height and weight for BMI, plus neck and waist measurements for body fat (and hip measurement for women).
Typical fat distribution differs between men and women, so the U.S. Navy method uses different measurements and coefficients for each.
It provides a reasonable estimate for most people, but is less precise than clinical methods and depends heavily on accurate measurements.
BMI doesn't separate muscle from fat, so muscular or athletic people can show a higher BMI despite low body fat.
No. This calculator is designed for adults. Children and teens need age- and sex-specific growth charts, and should be assessed by a pediatric professional.
Yes, tracking trends over weeks or months is generally more useful than any single measurement.
No. This tool provides general estimates for informational purposes only and does not replace individualized advice from a qualified healthcare professional.
Our Methodology
- BMI calculation method
- Standard Quetelet Index (weight ÷ height²)
- Body fat calculation method
- U.S. Navy circumference method
- Reviewed by
- [Qualified Reviewer Name — Replace Before Publishing]
- Written by
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- Last reviewed
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Sources
- Peer-reviewed research on BMI and body composition [Add citation]
- U.S. Navy circumference method validation studies [Add citation]
- Government or professional health organization guidance [Add citation]
Replace the source placeholders above with the references used to establish this calculator's methodology before publishing.
Health Disclaimer
This calculator provides estimated BMI and body fat percentage values for general informational purposes. It is not a medical diagnosis and does not replace individualized advice from a qualified healthcare professional. It is not intended for children, teenagers, or pregnant individuals.
If you have concerns about your weight, body composition, or overall health, please consult a qualified healthcare or nutrition professional.