Calorie Calculator
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Body Fat Calculator
A body fat calculator estimates what percentage of your weight is fat. Using the US Navy tape method, a man who is 180 cm tall with a 38 cm neck and 85 cm waist has about 16.1% body fat, which is in the “fitness” range. Women also measure their hips.
How to use this body fat percentage calculator
- Get a flexible tape. Use a soft tailor’s tape and measure on bare skin, first thing in the morning before eating.
- Measure your neck. Just below the larynx, with the tape sloping slightly downward at the front. Do not flare your neck.
- Measure your waist. Men measure horizontally at the navel; women at the narrowest point. Relax and breathe out normally.
- Women: measure hips. Measure around the widest part of the buttocks with feet together.
- Enter and repeat. Take each measurement twice and use the average. Re-measure every 2–4 weeks under the same conditions.
The US Navy method behind this navy body fat calculator
The method was developed by Hodgdon and Beckett at the Naval Health Research Center in 1984 and is still used by the US military for body composition standards. It predicts body fat from height and circumference measurements, because fat around the waist and hips grows faster than the neck as body fat rises.
Metric formulas (all measurements in cm):
- 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
Example: a man of 180 cm with a 38 cm neck and 85 cm waist. log10(47) = 1.672 and log10(180) = 2.255, giving 495 ÷ 1.062 − 450 = 16.1%.
What is a healthy body fat percentage?
The American Council on Exercise (ACE) uses these ranges for adults:
| Category | Men | Women |
|---|---|---|
| Essential fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | 25% or more | 32% or more |
Women carry more essential fat than men because of reproductive and hormonal needs, which is why the ranges differ. Going below the essential range can disrupt hormones, bone health and menstrual cycles.
Examples
| Person | Measurements | Body fat | Category |
|---|---|---|---|
| Man, 180 cm, 80 kg | Neck 38 cm, waist 85 cm | 16.1% | Fitness |
| Man, 180 cm, 88 kg | Neck 38 cm, waist 95 cm | 23.2% | Average |
| Woman, 165 cm, 60 kg | Neck 33, waist 70, hips 94 cm | 23.8% | Fitness |
| Woman, 165 cm, 65 kg | Neck 33, waist 75, hips 98 cm | 28.4% | Average |
Notice how 10 cm on the waist moves the first man’s estimate by about 7 points even though his weight changed by only 8 kg. Waist size is the single most important input.
Fat mass and the lean body mass calculator
Add your weight and the calculator splits it into fat mass and lean body mass (muscle, bone, organs and water). The 80 kg man above carries about 12.9 kg of fat and 67.1 kg of lean mass.
Tracking lean mass helps you judge a diet: if your weight drops but lean mass holds steady, you are losing fat rather than muscle. Lean mass is also used in some nutrition plans to set protein targets.
Waist-to-height ratio: a quick health check
Because you have already measured your waist and height, the calculator also shows your waist-to-height ratio. NICE in the UK advises keeping your waist to less than half your height:
- Under 0.5: healthy range
- 0.5 to 0.59: increased health risk
- 0.6 or more: high health risk
Central fat is linked with type 2 diabetes and heart disease, so this ratio is a useful second opinion alongside body fat percentage.
How accurate is a tape-measure method?
Compared with DEXA scans or underwater weighing, circumference methods are typically a few percentage points out for an individual. Errors are larger for very muscular people, people with a lot of abdominal fat, and when the tape is placed differently from one session to the next. Measure the same way each time and focus on the trend over several weeks.
Body fat calculator FAQs
Is the US Navy method accurate?
It is reasonable for most adults and much better than guessing from the mirror, but it can be a few percentage points out compared with a DEXA scan. It is best for tracking changes over time.
Why does the calculator ask women for hip size?
Women tend to store more fat around the hips and thighs, so the female formula uses waist plus hip minus neck to capture that.
Is body fat percentage better than BMI?
It tells you more about composition, since BMI cannot tell muscle from fat. A muscular person can have a high BMI and low body fat. Using both, plus waist-to-height ratio, gives the fullest picture.
How often should I measure?
Every 2–4 weeks is enough. Measure at the same time of day, before eating, and use the average of two readings.
Can I measure in inches?
Yes. Switch to imperial at the top of the calculator and enter height in feet and inches and measurements in inches.
Sources and methodology
Body fat uses the Hodgdon–Beckett (US Navy) circumference equations in their metric form with base-10 logarithms. Imperial inputs are converted to centimetres first. Categories follow the American Council on Exercise ranges. Fat mass = weight × body fat %. Waist-to-height ratio thresholds follow NICE guidance. All example figures were produced by this calculator.
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