Body Fat Percentage Calculator

What this body fat percentage calculator does

This calculator estimates your body fat percentage using the U.S. Navy Method. It also uses your age, sex, weight, height, and activity level to estimate your lean body mass and approximate daily maintenance calories. The tool is designed for general fitness and education, not for medical diagnosis.

Unlike BMI (Body Mass Index), which considers only height and weight, the Navy Method includes body measurements such as waist, neck, and hips (for women). That makes it more informative about body composition, especially for people who have above‑average muscle mass or who are actively training.

What is body fat percentage?

Body fat percentage is the proportion of your total body weight that is made up of fat tissue. For example, if you weigh 80 kg and 16 kg of that weight is fat, your body fat percentage is 20%. The remaining 80% is called lean body mass and includes muscle, organs, bones, water, and other non‑fat tissues.

Body fat percentage is often a better indicator of health and fitness than weight or BMI alone. Two people can have the same weight and height (and therefore the same BMI), but one may carry more muscle and less fat than the other. Measuring body fat helps you understand whether changes on the scale are mostly fat loss, muscle gain, or a mix of both.

How the U.S. Navy Method formula works

The U.S. Navy Method is a circumference‑based estimate of body fat. It was developed so that body composition could be assessed with simple tools (a measuring tape) instead of expensive equipment. The method uses logarithms of specific body measurements to approximate body density and then converts density to body fat percentage.

In simple terms:

• For men, the difference between waist and neck circumference, together with height, is used.
• For women, the sum of waist and hip circumferences minus neck circumference, together with height, is used.
• These measurements are plugged into formulas that estimate body density.
• Body density is then converted to body fat percentage using a standard equation.

A simplified representation of the male Navy body fat equation in MathML looks like this (logarithms are base 10):

The female equation is similar, but uses the sum of waist and hip minus neck instead of just waist minus neck. The calculator applies the appropriate version based on the sex you select and automatically handles units (centimeters or inches) internally.

How the calculator uses your inputs

Measurements

For the most consistent results, take measurements under similar conditions each time:

• Height: Stand straight against a wall without shoes. Measure from the floor to the top of your head.
• Neck circumference: Measure just below the Adam’s apple, keeping the tape horizontal and snug but not tight.
• Waist circumference: For men and women, measure at the narrowest point of your abdomen, roughly in line with the navel. Relax your abdomen and do not suck in your stomach.
• Hip circumference (women only): Measure at the widest part of the hips and buttocks, keeping the tape level around the body.
• Weight: Use a reliable scale. Weigh yourself under similar conditions (for example, in the morning before eating, with light clothing).

Age, sex, and activity level

Age and sex are used to pick the correct formulas and to interpret how typical or atypical your body fat result may be. Activity level is used along with your estimated Basal Metabolic Rate (BMR) to estimate daily maintenance calories.

• Sedentary: Mostly sitting, little to no structured exercise.
• Lightly active: Light exercise 1–3 days per week.
• Moderately active: Moderate exercise 3–5 days per week.
• Very active: Hard exercise 6–7 days per week.
• Extra active: Very hard daily training or physically demanding job.

From body fat to lean mass and calories

Once the calculator has estimated your body fat percentage, it can break your body weight into two parts:

• Fat mass = total body weight × (body fat percentage ÷ 100)
• Lean body mass = total body weight − fat mass

For calorie estimates, the calculator uses a standard BMR equation (such as Mifflin‑St Jeor or a similar method) based on your age, sex, height, and weight. BMR is then multiplied by your selected activity factor to estimate your total daily energy expenditure (sometimes called maintenance calories).

In plain language:

• BMR is how many calories your body would burn in 24 hours if you rested all day.
• Maintenance calories is an estimate of how many calories you burn in a typical day including movement, work, and exercise.

You can use these values to guide your goals:

• To maintain weight, many people aim to eat close to maintenance calories.
• To lose weight, a modest calorie deficit (for example, 250–500 kcal below maintenance) is often used under professional guidance.
• To gain weight, a small calorie surplus is usually chosen, especially when combined with resistance training.

These are general guidelines only. Individual needs vary, so discuss specific calorie targets with a qualified health professional or registered dietitian.

Interpreting your body fat percentage

The ranges below are based on commonly cited guidelines such as those from the American Council on Exercise (ACE). Exact cut‑offs may differ slightly between organizations and sources.

• Essential fat
  Men: about 2–5%
  Women: about 10–13%
  This level supports basic physiological functions. It is not usually a target range except for specific medical or elite athletic contexts.
• Athletes
  Men: about 6–13%
  Women: about 14–20%
  Common in competitive sports where low body fat is advantageous and closely supervised.
• Fitness
  Men: about 14–17%
  Women: about 21–24%
  Typical for active individuals with visible but not extreme muscular definition.
• Acceptable
  Men: about 18–24%
  Women: about 25–31%
  Common among the general population. Many people maintain good health within this range, depending on lifestyle, genetics, and other factors.
• Obesity
  Men: roughly 25% and above
  Women: roughly 32% and above
  Higher body fat levels are associated with increased risk of cardiometabolic conditions, but risk also depends on where fat is stored, family history, and other health markers.

If your result falls outside the ranges you expected, avoid making drastic changes immediately. Instead, use it as one data point, along with how you feel, your performance, medical history, and feedback from health professionals.

Worked example

The numbers below are for illustration only and are not a recommendation.

Imagine a 30‑year‑old man with the following measurements:

• Height: 178 cm
• Neck: 38 cm
• Waist: 86 cm
• Weight: 80 kg
• Activity level: Moderately active

The calculator would:

1. Convert measurements to the correct units for the Navy formula if needed.
2. Apply the male Navy equation using waist, neck, and height.
3. Estimate body fat percentage (for example, around the mid‑teens to low‑20s, depending on exact measurements).
4. Compute fat mass (body weight × body fat percentage).
5. Compute lean body mass (body weight minus fat mass).
6. Use age, weight, height, and sex to calculate BMR.
7. Multiply BMR by an activity factor corresponding to “Moderately active” to estimate maintenance calories.

You can then compare the resulting body fat percentage to the interpretation ranges above and decide, ideally with professional support, whether to focus on fat loss, muscle gain, or weight maintenance.

Comparison of body fat measurement methods

The Navy Method is one of several ways to estimate body fat. Each method has its own trade‑offs between cost, convenience, and accuracy.

For most people, the Navy Method offers a practical compromise between convenience and information. If you need a clinical assessment of body composition, discuss more advanced methods with your healthcare provider.

Limitations, assumptions, and safety notes

This calculator provides estimates, not definitive measurements. Several assumptions are built into the Navy Method and the calorie equations:

• The formulas are based on data from generally healthy adults. Accuracy may be lower in children, adolescents, older adults, and people with certain medical conditions.
• Very muscular individuals (for example, strength athletes and bodybuilders) may receive higher estimated body fat percentages than they actually have.
• People with unusual fat distribution (such as very narrow or very wide waists relative to height) may also see less accurate results.
• The method is not validated for pregnancy. Pregnant people should not rely on this calculator to track body fat and should follow medical advice instead.
• Small changes in how and where you place the tape can shift the estimate by several percentage points. Always measure in a consistent way.
• BMR and maintenance calorie estimates are averages. Real‑world energy needs can differ based on genetics, health status, hormone levels, medications, and day‑to‑day activity patterns.

Because body fat and calorie intake relate to health outcomes, keep the following safety points in mind:

• Do not use this tool to self‑diagnose any disease or to replace medical tests or advice.
• Avoid extreme low‑calorie diets, rapid weight loss programs, or overtraining in response to a single body fat estimate.
• If you have a history of eating disorders, body image concerns, or significant medical conditions, discuss your goals and tracking methods with a qualified professional before acting on these numbers.
• If your result is very high or very low and you are worried about your health, consult a doctor or registered dietitian for an individualized assessment.

By using this calculator, you accept that results are approximate and for informational and educational purposes only.

How to use your results constructively

Treat your body fat percentage as one metric among many, alongside strength, stamina, energy levels, sleep quality, and lab results where appropriate. Useful next steps might include:

• Tracking measurements and estimates over time (for example, every 4–8 weeks) rather than focusing on a single reading.
• Combining body fat tracking with simple performance tests, such as walking or running pace, lifting strength, or flexibility.
• Discussing goals (such as fat loss, muscle gain, or performance) with a coach, trainer, or healthcare professional who can help design a safe plan.
• Exploring related tools such as BMI, BMR, or total daily energy expenditure (TDEE) calculators to see how different metrics fit together.

Sustainable changes in body composition usually come from a combination of regular physical activity, adequate sleep, stress management, and a balanced diet that you can maintain long term, not from quick fixes or extreme restrictions.