2026-08-07 10 min

Body Fat Percentage Calculator

Estimate body fat percentage from tape measurements and weight with the US Navy method, plus fat mass, lean mass, BMI, and your age-adjusted ideal target.

Calculator

Gender

Units

Age

yrs

18 to 100; sets the age-adjusted ideal

Height

Barefoot height

Weight

Morning scale weight

Neck

Below the larynx, tape level

Waist

At the navel, end-exhale

Hip

Widest point; female equation

Results update live as you type

Status:Body fat 17.0% (Average)Ideal 12.7%

Body Fat Results

Body Fat %17.0%

CategoryAverage

Fat Mass13.6

Lean Mass66.4

To Reach Ideal3.9

Composition Breakdown

Measure	Value
Body fat	17.0% (Average)
Fat mass	13.6 kg
Lean mass	66.4 kg
BMI	26.1
Ideal (age-adjusted)	12.7%

Recommendations

▸About 3.9 kg of fat loss reaches the age-adjusted ideal of 12.7% if lean mass is preserved
▸Re-measure monthly with the same tape, landmarks, and morning timing

Results

Optimal

Body Fat %

17.0%

Navy estimate (Average)

Visualizations

Composition Breakdown

13.6Fat

66.4Lean

Fat vs Lean Mass

Fat mass17%

Lean mass83%

Body Fat Level

Body fat17%

Formula

The Hodgdon-Beckett Navy equations regress body fat on circumference differences and height. Metric tapes convert to inches before the log terms run.

Male: BF% = 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76

Alternative Form

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

Variables

Symbol	Name	Unit	Description
BF%	Body fat percentage	%	Estimated share of body weight that is fat
W, N, H	Waist, neck, hip	in	Tape circumferences; hip is used in the female equation only
Ht	Height	in	Barefoot standing height
Wgt	Body weight	kg/lbs	Scale weight for the fat and lean split
BMI	Body mass index	kg/m2	Weight over height squared, reported alongside body fat

Explanation

Log differences compress large circumferences the way body fat scales, and height enters negatively so taller builds compute leaner at equal tapes.

Derivation

Convert cm to inches at 2.54. Fat mass = BF% x weight. Lean mass = weight - fat. Ideal comes from Jackson and Pollock age interpolation.

Step-by-Step Calculation

Follow each step to understand how the result is calculated from your inputs.

Step 1

Convert tapes to inches for the Navy equations.

inches = cm / 2.54

Height:175 cm

Waist:85

Neck:38

Intermediate: Metric inputs divide by 2.54

Result: Log domain checks pass

Step 2

Form the log argument from the circumference difference.

Male: log10(waist - neck); Female: log10(waist + hip - neck)

Gender:male

Intermediate: Differences remove frame size from the waist signal

Result: Argument is positive, logs defined

Step 3

Apply the Hodgdon-Beckett equation.

BF% = a x log10(diff) - b x log10(height) + c

Measured:17.0%

Intermediate: Male a=86.010 b=70.041 c=36.76; Female a=163.205 b=97.684 c=-78.387

Result: Body fat = 17.0%

Step 4

Split scale weight into fat and lean compartments.

Fat = BF% x weight; Lean = weight - fat

Weight:80 kg

Intermediate: 0.1701 x weight

Result: Fat 13.6, lean 66.4

Step 5

Compute BMI for context from the same height and weight.

BMI = weight(kg) / height(m)^2

BMI:26.1

Intermediate: BMI screens weight, body fat screens composition

Result: BMI 26.1

Step 6

Look up the age-adjusted ideal and the fat to lose.

Target weight = lean / (1 - ideal)

Ideal:12.7%

Intermediate: Jackson and Pollock interpolation by age and gender

Result: 3.9 to lose at constant lean mass

Final Answer

17.0%

Worked Examples

See how the calculator works with different scenarios.

Scenario

A 30-year-old male, 175 cm, 80 kg, neck 38 cm, waist 85 cm.

Inputs

Gender:male

Height:175 cm

Weight:80 kg

Neck:38 cm

Waist:85 cm

Calculation

Waist - neck = 47 cm = 18.5 in; height = 68.9 in. BF% = 86.010 x log10(18.5) - 70.041 x log10(68.9) + 36.76 = 17.0%. Fat = 17.0% x 80 = 13.6 kg.

Result

17.0% body fat (Average); fat 13.6 kg, lean 66.4 kg, BMI 26.1

Interpretation

An average-band result with an overweight BMI — a classic case where composition beats BMI for the real verdict.

Understanding Your Result

Your Result: Body Fat %: 17.0%

Typical range: Typical tape results run 12-22% for active men and 22-32% for active women. Fitness bands are 14-17% for men and 21-24% for women.

What This Means

The headline percentage is the Navy tape estimate, split into fat mass and lean mass with an ACE category and an age-adjusted ideal target.

Why It Matters

Scale weight cannot tell fat from muscle. The percentage plus the fat and lean split shows whether to cut, hold, or recomp.

Professional Interpretation

Treat within-2-point moves as noise. Trend the monthly average and confirm big decisions with waist, photos, and strength numbers.

Recommendations

•Above ideal: plan roughly 0.5% of body weight loss per week
•At ideal: eat near maintenance with 1.6-2.2 g of protein per kg
•Re-measure monthly with identical technique and timing
•Add waist trend and photos beside the percentage
•Lift 2-4 times weekly to protect lean mass in a deficit

Educational Content

Introduction

This calculator turns a tape measure and a scale into a body fat estimate with the US Navy equations, then splits weight into fat and lean compartments.

Concept Explanation

Circumference differences predict body fat because abdominal fat scales with waist after removing frame size via the neck. Height normalizes tall versus short builds through a negative log term.

Applications

▸First body composition check without calipers or scans

▸Monthly cut or bulk tracking with one consistent method

▸Comparing BMI against actual composition

▸Setting a fat-loss target from the age-adjusted ideal

▸Pre-screening before military or program tape tests

Benefits

•Needs only a tape and a scale — no lab visit
•Splits weight into actionable fat and lean numbers
•Includes an age-adjusted ideal, not just a raw percent
•Works in metric or imperial with automatic conversion
•Instant recalculation supports what-if planning

Limitations

•Field estimate with 3-4 points of error versus DEXA
•Single-day food, water, and pump shift the tapes
•Technician landmark skill dominates accuracy
•Cannot diagnose health conditions alone

Best Practices

•Tape fasted in the morning on bare skin
•Level the tape and read at end-exhale
•Average three pulls per site
•Verify barefoot height; never reuse a stale value
•Track monthly, not daily

Common Misconceptions

Myth: The tape measures fat directly.

Truth: It predicts fat from circumferences with a regression. Only scans partition tissue directly.

Myth: BMI and body fat are the same.

Truth: BMI screens weight for height; body fat screens composition. Muscular builds break BMI but not the tape split.

Myth: A single reading defines you.

Truth: Tape noise is real. The 4-week trend is the result; one morning is a data point.

Practical Tips

•Measure first thing in the morning before food for repeatable numbers
•Use the same tape, scale, and landmarks every time
•Average three tape pulls per site instead of trusting one
•Track the 4-week trend, not day-to-day noise
•Pair the scale with waist and progress photos
•Re-run the numbers after every 3-5 kg of weight change

Common Mistakes

Comparing different methods as if they match

Pick one method and track it. Navy, skinfold, and DEXA can differ by 3-5 points on the same body.

Measuring after meals or training

Food, water, and pump change weight and circumferences. Measure fasted and rested.

Pulling the tape too tight or too loose

Snug without compressing skin, level, at end-exhale. Practice the same tension each time.

Chasing daily fluctuations

Weigh 3-4 times per week and compare weekly averages; fat loss is a trend.

Cutting calories so hard that muscle is lost

Keep protein near 1.6-2.2 g per kg and lift 2-4 times weekly while in a modest deficit.

Assumptions

This calculator makes the following assumptions to provide estimates:

Fat-only change model: Goal math assumes fat is lost while lean mass is preserved through protein and training.

Stable hydration: Readings assume normal hydration; dehydration and glycogen swings shift weight and tapes.

Consistent technique: Tape landmarks, tension, and timing match between measurements.

Adult norms: ACE bands and ideals apply to adults 18 and over, not children or athletes under supervision.

Energy math: One kilogram of body fat is treated as about 7,700 kcal for timeline estimates.

Limitations

Be aware of these limitations when using this calculator:

Estimate, not a scan: Field equations carry 3-4 points of error versus DEXA; treat results as a working estimate.

Single-day variability: Food, sodium, sleep, and training move weight and waist day to day.

No medical diagnosis: This tool screens composition; it does not diagnose obesity or metabolic disease.

Muscle confounds weight math: Very muscular builds read heavier at the same leanness; photos and strength track progress too.

Frequently Asked Questions

Answers to common questions about this calculator.

What is body fat percentage?

Body fat percentage is the share of total body weight made of fat tissue. It describes composition, while scale weight alone cannot tell fat from muscle.

How does the Navy method estimate body fat?

It applies a log regression to neck, waist, hip, and height. The equation was fit against laboratory measurements and works with a tape and scale.

How accurate is this estimate?

Expect about 3 to 4 points of error versus DEXA for most adults. Technique and timing matter more than the arithmetic.

Where do I measure my waist?

At the navel, tape horizontal, at the end of a normal exhale. Do not suck in or compress the skin.

Where do I measure my neck?

Just below the larynx with the tape level and shoulders relaxed. Look straight ahead.

Why do women enter hips?

Women store more fat on hips and thighs, so the female equation adds the hip term to capture that compartment.

What is a healthy body fat percentage?

ACE suggests men 18 to 24% and women 25 to 31% as average, with fitness at 14 to 17% for men and 21 to 24% for women.

What are fat mass and lean mass?

Fat mass is weight times body fat percent. Lean mass is everything else: muscle, bone, water, and organs.

How much should I weigh at my ideal body fat?

Divide current lean mass by one minus the ideal fraction. The calculator shows this as kilograms or pounds to lose if lean mass holds.

Can body fat be too low?

Yes. Below about 5% for men or 10 to 13% for women risks hormones, bone, immunity, and cycle disruption.

Why does height change the result?

Height enters with a negative coefficient, so taller people compute leaner at equal tapes. Enter true barefoot height.

How often should I retest?

Monthly is plenty. Weekly averages of weight plus a monthly tape give a clean trend without noise.

Related Calculators

Explore more calculators related to this topic.

Related Guides

Deepen your understanding with these educational resources.

Body Composition Basics

Fat mass, lean mass, and what healthy ranges look like.

How to Cut Without Losing Muscle

Protein, lifting, and deficit sizing for fat loss.

Tape-Measure Best Practices

Landmarks, tension, and timing for repeatable readings.

Glossary

Technical terms used in mortgage calculations explained in plain language.

Body fat percentage: Share of total body weight made up of fat tissue, expressed as a percent.
Fat mass: Kilograms or pounds of body weight that are fat tissue.
Lean mass: Body weight minus fat mass: muscle, bone, water, and organs.
Essential fat: Minimum fat needed for normal physiology; about 2-5% for men and 10-13% for women.
ACE categories: Athlete, fitness, average, and obese bands published by the American Council on Exercise.
Siri equation: Body fat percent from body density: (495 / density) - 450.
Body density: Body mass divided by body volume; estimated from skinfolds or circumferences.
Calorie deficit: Eating fewer calories than burned, forcing the body to use stored fat.
Recomposition: Losing fat while preserving or gaining lean mass through training and protein.
Plateau: A stall in fat loss, usually from adaptation, tracking drift, or water retention.

Authoritative References

Trusted sources and standards referenced by this calculator.

American Council on Exercise — Body Fat Percentage CDC — Healthy Weight Assessment Jackson & Pollock — Generalized equations for predicting body density Hodgdon & Beckett — Prediction of percent body fat (Navy method) Deurenberg et al. — Body mass index as a measure of body fatness NIH — Clinical Guidelines on Overweight and Obesity WHO — Obesity and overweight fact sheet

Applicable Standards

ACE body fat percentage normsJackson & Pollock age-adjusted idealsWHO healthy weight guidance

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Page Information

Last Updated:

2026-08-07

Version:

2.0.0

References:

License:

Free to use for educational and professional purposes.