Body Fat Calculator
Estimate your body fat percentage using the US Navy method.
What Is Body Fat Percentage?
Body fat percentage is the proportion of fat mass to total body weight. Unlike BMI, which only considers height and weight, body fat percentage directly measures how much of your body is composed of fat versus lean tissue (muscle, bone, organs, and water). It is a more accurate indicator of fitness and metabolic health.
US Navy Method Formula
The US Navy method estimates body fat using circumference measurements. All measurements should be taken at the narrowest/most consistent point and logged in the same unit (cm or inches).
Males:
BF% = 495 ÷ (1.0324 − 0.19077 × log₁₀(waist − neck) + 0.15456 × log₁₀(height)) − 450
Females:
BF% = 495 ÷ (1.29579 − 0.35004 × log₁₀(waist + hip − neck) + 0.22100 × log₁₀(height)) − 450
Body Fat Category Chart
Category ranges differ by gender. The American Council on Exercise (ACE) provides these widely-referenced guidelines:
| Category | Male | Female |
|---|---|---|
| Essential Fat | 2–5% | 10–13% |
| Athletes | 6–13% | 14–20% |
| Fitness | 14–17% | 21–24% |
| Average | 18–24% | 25–31% |
| Obese | ≥25% | ≥32% |
How to Measure
- Neck: Measure just below the larynx (Adam's apple), keeping the tape horizontal.
- Waist: For men, measure at the navel. For women, measure at the narrowest point of the natural waist.
- Hip (women only): Measure at the widest point of the hips/buttocks.
- Height: Stand straight against a wall without shoes.
For best results, take measurements in the morning before eating and repeat 2–3 times, using the average.
Example: Calculating Body Fat Percentage
Consider a 30-year-old man who is 175 cm (68.9 inches) tall, with a neck circumference of 38 cm (15 inches) and a waist of 85 cm (33.5 inches). Using the US Navy formula for males: BF% = 495 ÷ (1.0324 − 0.19077 × log₁₀(33.5 − 15) + 0.15456 × log₁₀(68.9)) − 450. Working through the log terms, this produces a body fat percentage of approximately 15–16%, which falls in the "Fitness" category. If he weighed 75 kg, his body fat mass would be roughly 11.6 kg and his lean body mass about 63.4 kg. Use this calculator to enter your own measurements and see where you fall on the category chart.
Body Fat Percentage vs. BMI: Which Is Better?
BMI (Body Mass Index) is a quick screening tool that uses only height and weight, but it cannot distinguish between muscle and fat. This creates well-known limitations: a muscular athlete may register as "overweight" by BMI despite having low body fat, while someone with normal weight but high fat mass (sometimes called "skinny fat") may appear healthy by BMI alone. Body fat percentage avoids this problem by directly estimating fat mass. For fitness tracking and body recomposition goals, body fat percentage is the more meaningful metric. However, BMI remains useful for population-level health screening because it is fast, free, and requires no measurements beyond height and weight.
How to Lower Your Body Fat Percentage
Reducing body fat requires a sustained calorie deficit — consuming fewer calories than you burn. Strength training is critical because it preserves or builds muscle while you lose fat, ensuring that weight lost comes from fat rather than lean tissue. Aim for 2–4 strength sessions per week targeting all major muscle groups. Combine this with adequate protein intake (roughly 0.7–1 gram per pound of body weight) to support muscle maintenance. Cardio can increase your calorie burn, but diet typically drives the deficit. Avoid crash diets, which can cause muscle loss and slow your metabolism. A moderate deficit of 300–500 calories per day supports steady fat loss of 0.5–1 pound per week while preserving muscle.
Factors That Affect Accuracy
The US Navy method is sensitive to measurement precision. Small changes in waist or neck circumference can shift your result by 1–2%. To improve reliability:
- Use a flexible, non-stretch measuring tape rather than a ruler or string.
- Measure at the same time of day, ideally in the morning before eating or drinking.
- Have a second person help you to ensure the tape stays horizontal and snug but not compressing the skin.
- Take each measurement 2–3 times and use the average to reduce random error.
- Avoid measuring immediately after a large meal or workout, which can temporarily alter circumference.
Even with careful technique, expect your result to fluctuate by 1–3% between measurements. Track the trend over weeks rather than fixating on any single number.
Healthy Ranges and Essential Fat
Body fat is not inherently bad — your body requires a minimum amount of fat to regulate hormones, protect organs, and store vitamins. This "essential fat" is roughly 2–5% for men and 10–13% for women. Dropping below these levels can impair hormone production, immune function, and overall health. For most people, a sustainable and healthy range is 10–20% for men and 18–28% for women. Athletes may sit lower for performance reasons, but maintaining very low body fat long-term is difficult and not necessarily healthier. Use the category chart above as a general guide, and consult a healthcare provider for personalized targets.
Frequently Asked Questions
The US Navy method is reasonably accurate (typically within 3–4% of DEXA scans) when measurements are taken carefully. It is a convenient and free alternative to clinical methods like hydrostatic weighing or DEXA. For the best results, measure consistently at the same time of day and have someone help you with the tape.
BMI uses only height and weight to estimate whether your weight is in a healthy range, but it cannot distinguish between muscle and fat. Body fat percentage directly measures fat mass. Two people with the same BMI can have very different body fat percentages — for example, a muscular athlete may have a high BMI but low body fat.
For men, a body fat percentage of 10–20% is generally considered healthy, while for women 18–28% is healthy. Women naturally carry more essential fat. Going below essential fat levels (under 5% for men or under 13% for women) can be dangerous and may impair hormone function and overall health.
The US Navy formula itself only needs height and circumference measurements. Your weight is used to calculate the secondary outputs: body fat mass (your total weight × body fat percentage) and lean body mass (your weight minus body fat mass). These help you understand your body composition in absolute terms.