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BMI Calculator
Body Mass Index with WHO classification and healthy weight range.
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Body Fat Calculator
Estimate body fat % using Navy method or BMI method. No signup — your inputs stay in your browser.
Step By Step
How to Use This Calculator
4 steps
- Choose Navy Method (tape) for the most accurate estimate — or BMI Method if you only have weight and height.
- Select your sex. For females on the Navy method, a Hip field will appear.
- Enter height in cm or ft+in, weight in kg or lbs. Waist, neck, and hip can each be entered in cm or inches.
- Waist: measure at the navel. Neck: just below the larynx. Hip (women): at the widest point.
Worked Example
Example: Male, Navy method — height 175 cm, waist 85 cm, neck 38 cm
Use this sample to sanity-check your inputs and understand what the final result represents.
- 186.010 × log₁₀(85 − 38) = 86.010 × 1.672 = 143.8
- 270.041 × log₁₀(175) = 70.041 × 2.243 = 157.1
- 3BF% = 143.8 − 157.1 + 36.76 = 23.5%
Final Result
23.5% → Acceptable range (ACE male classification)
Methodology
US Navy Tape Method (Hodgdon & Beckett, 1984)
This section explains the calculation logic, assumptions, and source material used to make the result more trustworthy and easier to verify.
Male: 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76. Female: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387. All values in cm. Inches are converted automatically (1 in = 2.54 cm). BMI method uses Deurenberg et al. (1991): Male (1.20 × BMI) + (0.23 × age) − 16.2.
Frequently Asked Questions
What is the Navy tape method and how accurate is it?+
The US Navy tape method estimates body fat from circumference measurements — waist, neck, and hip (women only). It was developed by Hodgdon and Beckett in 1984 for field use where body composition equipment wasn't available. Studies show it has a standard error of about 3–4% body fat compared to underwater weighing, which is reasonable for a tape-only measurement. It tends to be less accurate at very high or very low body fat levels.
Why does the female formula include hip measurement?+
Women naturally store more fat around the hips and thighs than men of equivalent overall body fat percentage — a pattern called gynoid fat distribution. Leaving hip out of the female formula would significantly underestimate body fat. The male formula omits it because men store proportionally far less fat in that region.
Where exactly do I measure waist, neck, and hip?+
Waist: at the navel (belly button level), not the narrowest point. Neck: just below the larynx (Adam's apple), with the tape sloping slightly downward from front to back. Hip (women): at the widest point across the buttocks. Keep the tape horizontal, snug but not compressing the skin, and measure after exhaling normally.
What is the BMI method and when should I use it?+
The BMI method (Deurenberg formula, 1991) estimates body fat from BMI, age, and sex. It requires no tape measurement, just weight and height. It's less accurate than the tape method — particularly for athletes — but useful when you can't take circumference measurements. Expect results to be rougher, especially if you have high muscle mass.
What are ACE body fat categories?+
The American Council on Exercise (ACE) divides body fat into five categories: Essential fat (the bare minimum for body function), Athletes, Fitness, Acceptable, and Obese. These are reference ranges based on health outcomes research, not absolute cutoffs. Two people with the same body fat percentage can have very different health profiles depending on where fat is stored.
Is body fat percentage better than BMI?+
For body composition specifically, yes — body fat percentage actually measures what BMI tries to approximate. BMI can't distinguish muscle from fat, so a muscular person reads as 'overweight' on BMI but may have perfectly healthy body fat. That said, body fat from a tape measure still has error, and neither replaces a full health assessment.