What is body fat percentage?

Body fat percentage estimates how much of your body weight is fat mass versus fat-free mass (muscle, bone, water, organs). It’s more informative than BMI because it looks at composition.

How accurate is this Body Fat Calculator?

It uses circumference-based equations (often called the U.S. Navy method) for a good field estimate. It’s not as precise as DEXA or hydrostatic weighing, but it’s consistent for trends.

What measurements do I need?

Height, weight, and tape measurements (waist and neck; women also include hip). Measure level and snug, preferably in the morning for consistency.

Can BMI replace body fat percentage?

No. BMI doesn’t distinguish fat from muscle. Body fat % better reflects composition.

What are healthy body fat ranges?

Men: essential 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, obesity 25%+. Women: essential 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, obesity 32%+.

Do hydration or time of day affect results?

Yes, they can nudge circumferences. Measure at similar times to keep readings comparable.

Is this calculator suitable for children?

It’s designed for adults. Children and teens require different reference ranges.

How do I lower body fat safely?

Use a modest calorie deficit, adequate protein, resistance training, and sleep. Aim for slow, steady change to preserve muscle.

Body Fat Calculator

Estimate body fat using the U.S. Navy method, then view fat mass, lean mass, and an age-adjusted ideal range.

Units

Sex

Age (years)

Height (in)

Weight (lb)

Neck (in)

Waist (in)

Hip (in) — women

Body Fat (U.S. Navy)

—

Category: —

Fat Mass

—

Lean Mass: —

BMI

—

How this body fat calculator works

The U.S. Navy method estimates body fat % from circumference measurements. For men it uses waist, neck, and height. For women it uses waist, hip, neck, and height. Results are estimates and can differ from DEXA or calipers.

Formulas

Male: BF% = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76

Female: BF% = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387

All measurements in inches; the tool converts metric to imperial internally.

Body Fat Percentage: A Practical Guide to Measuring, Interpreting, and Improving

Body fat percentage is a snapshot of how much of your body is composed of fat versus everything else—muscle, bone, water, and organs. It can be a clearer indicator of body composition than weight alone because it separates fat from lean mass. The calculator above uses a proven circumference approach to give you a quick estimate that you can track over time. Below is a practical guide that explains how to take measurements accurately, what your number may mean, how to set realistic goals, and how to use this estimate alongside other tools to make better decisions.

How to take accurate measurements

Small differences in tape placement can shift your result. Take two or three readings at each site and use the average. Measure at the same time of day, under similar conditions (hydration, food, training), and with the same tape measure.

For men (waist, neck, height)

Waist: Horizontal at the level of the navel. Relax the abdomen, don’t suck in.
Neck: Just below the larynx (Adam’s apple), tape slightly angled downward to the front.
Height: Stand tall, heels together, back against a wall if possible.

For women (waist, hip, neck, height)

Waist: Narrowest point between ribs and hips or at the navel—be consistent.
Hip: Widest point around the buttocks, feet together.
Neck: Just below the larynx, same as men.
Height: As above—consistent posture matters.

Use gentle tension—tight enough to remove slack but not compressing soft tissue.
Take two to three readings for each site; if one is a clear outlier, discard it and retake.
Log the exact tape positions you used so you can repeat them later.

Understanding your number in context

Body fat ranges overlap with health and performance outcomes, but there is no perfect percentage for everyone. Genetics, age, training history, and personal preference all matter. Rather than chasing a single number, use your estimate to guide trends and decisions.

Performance: Strength athletes often perform well across a broad range; endurance athletes may prefer lower ranges for power-to-weight.
Appearance: The same percentage can look different depending on muscle mass, height, and fat distribution.
Sustainability: Extremely low levels can be hard to maintain and may reduce energy, mood, or recovery.

Setting a realistic target

Meaningful change happens gradually. A typical sustainable pace for fat loss is about 0.5–1.0% of body weight per weekfor most people, slower for leaner individuals. For muscle gain, the scale may rise while body fat % holds steady or increases slightly, depending on diet and training.

Short-term horizon (4–8 weeks): Focus on consistent habits—nutrition, steps, sleep—while monitoring the trend.
Medium-term (8–16 weeks): Adjust calories or activity based on how your weight and measurements move.
Long-term: Use periodic maintenance phases to consolidate progress and avoid “yo-yo” cycles.

Why circumference methods work

The Navy equations use logarithms of circumferences because the relationship between girth and body fat is non-linear. As waist or hip measurements expand relative to neck and height, the model predicts higher fat mass. While not a direct measure, it’s practical: tapes are inexpensive, portable, and repeatable with a bit of practice.

Strengths and limitations

Strengths

Quick and inexpensive—no special equipment beyond a tape measure.
Useful for tracking direction of change over time.
Works across a wide range of body types with basic guidance.

Limitations

Assumes average fat distribution; unusual patterns can skew results.
Measurement error (tape angle, tension) can add noise.
Hydration, bloating, and posture can shift waist readings day-to-day.

How it compares to other approaches

DEXA: Often used in research and clinics; provides segmental data (arms/legs/torso). Accurate but costlier and not always available.
Skinfold calipers: Good when used by a trained practitioner; sensitive to technique and site selection.
Bioelectrical impedance: Convenient scales or handhelds; influenced by hydration and recent meals.
Hydrostatic or Bod Pod: Specialized equipment estimating body density; accurate but impractical for frequent use.
Visual methods: Photo comparisons can help corroborate trends when done with consistent lighting and poses.

No method is perfect. What matters most is consistency: repeat the same method under similar conditions and evaluate the trend over weeks, not days.

Improving accuracy and consistency

Timing: Measure in the morning after using the restroom and before eating or training.
Hydration: Stay consistent; big swings can change waist readings.
Posture: Stand tall, relax shoulders, and breathe normally—don’t brace or suck in.
Tape placement: Mark measurement spots lightly on the skin if you struggle to repeat them.
Repeat & average: Take two or three measurements per site and average them.

From a number to next steps

Body fat % is just one input. Pair it with a simple weight trend and how your clothes fit to get a fuller picture. If your goal is fat loss and the trend stalls for two to three weeks, gently increase activity (like step count) or adjust average calorie intake. If your goal is muscle gain, a slow upward trend in weight with stable or slightly rising body fat % is common—progress can be evaluated by strength numbers, photos, and how you feel.

Training: Prioritize resistance training two to four days per week to preserve or build lean mass.
Protein: A common target is about 1.6–2.2 g/kg of body weight per day, adjusted to preference and tolerance.
Sleep: Aim for 7–9 hours; poor sleep undermines recovery and appetite regulation.
Steps: Daily movement (e.g., 6–10k steps) helps manage energy balance without exhausting workouts.

Example: reading the output

Suppose a 180 lb (82 kg), 70 in (178 cm) male records 34 in waist and 16 in neck. The calculator estimates around the high-teens to low-twenties for body fat %. If his target is closer to 15%, a practical plan could be:

Set a moderate calorie deficit for a projected 0.5–0.75 lb (0.25–0.35 kg) weekly loss.
Lift weights three days a week and walk most days.
Hit a steady protein target; distribute across meals.
Measure circumferences and weight twice per week; average them.
Assess after three to four weeks; adjust only if the trend isn’t moving.

Common pitfalls (and easy fixes)

Inconsistent tape placement: Fix by marking sites or using landmarks (navel level, widest hip point).
Measuring after large meals: Morning fasted measurements remove this variable.
Over-focusing on single readings: Look at weekly averages and multi-week trends.
Chasing aggressive timelines: Sustainable change beats crash diets for long-term results.

Frequently asked questions

Does training before measuring change the result? It can. Lifting or core work can cause temporary muscle pump or posture changes that affect tape placement. Measure before workouts when possible.

Can I improve the estimate without buying new tools? Yes—be precise with tape technique, use averages, and measure under consistent conditions. Adding progress photos in the same lighting helps corroborate changes.

What if my readings bounce around? Day-to-day noise is normal. Compare weekly averages and look for a direction over two to four weeks rather than reacting to single points.

Should I use multiple methods? If you can, yes. For example, use this calculator weekly and take monthly caliper or DEXA measurements if accessible. The combination can give you confidence in the trend.

This guide is for education only and is not a substitute for personalized medical or nutrition advice.