Body Fat Calculator
Estimate body fat percentage with the U.S. Navy circumference method. Just a measuring tape — no calipers, scales, or scans needed.
- Runs in your browser
- Private processing
- No uploads
01Why this body fat tool
Composition, without calipers.
Four reasons this page beats the bathroom-scale 'body fat %' reading or a guess.
- 01
U.S. Navy circumference method
A well-validated formula that uses a flexible tape measure — no calipers, no bioelectrical scale, no expensive lab visit.
- 02
Men and women equations
Different inputs for each — neck and waist for men; neck, waist, and hips for women. The tool handles the formula difference automatically.
- 03
Live results as you measure
Type each measurement and watch your estimate update. Great for trying different tape positions to see how sensitive the result is.
- 04
Everything stays local
Measurements live in your tab and disappear when you close it. Nothing leaves your device.
02How it works
Tape, type, read.
- InputsMetricImperial
Step 1Pick units and sex
Toggle metric or imperial. Pick the sex-specific equation — men use neck and waist; women add hips.
- Tape readingsNeck38cmWaist85cmHips—cm
Step 2Measure with a soft tape
Around the smallest part of the neck, around the waist (at the navel for men, at the narrowest point for women), and around the widest part of the hips.
- Body fat17.4%Fit · adult male
Step 3Read your body fat %
Estimate appears with a color-coded fitness band (athlete, fit, average, high). Use it as a baseline and re-measure on the same schedule.
03Use cases
Where body fat % matters.
Cuts, recomps, intake forms, BMI tie-breakers — everywhere the scale alone falls short.
Track a recomp
Trying to lose fat while preserving muscle? Body fat % is the more honest signal than the scale — weight can hold steady while composition improves.
Monthly tracking · trend downPair with BMI for context
BMI says 'overweight' but you lift; body fat says you're fine. The two together resolve the most common false alarm in fitness math.
BMI 27 · body fat 14%Set a realistic cut goal
Pick a target body fat for the end of a cut, not just a weight. Helps avoid losing muscle along with fat.
Cut goal · 12% body fatCalorie planning input
Body fat estimate informs lean mass, which informs protein and calorie targets. Combine with TDEE for a complete plan.
LBM input for TDEEPre-medical screening
Some clinics ask for body fat estimates alongside BMI. The Navy method is well-known and easy to reproduce.
Clinic intake formLong-term trend tracking
Take the same measurement every two weeks at the same time of day. Trend lines beat single-day readings every time.
Every-two-week cadence
04Quick tips
Measure consistently.
Four habits that make body-fat estimates trend-worthy, not noise.
- 01
Measure morning, post-bathroom, pre-food
Water and food shift waist measurements by an inch. Standardize the conditions for trend tracking to be meaningful.
- 02
Tape position matters
Waist at the navel (men) or narrowest point (women). Tape level, snug but not compressing. Same position every time.
- 03
Estimates have margins of error
Navy method typically lands within 3–4 percentage points of DEXA on the average adult. Use it as a tracker, not a diagnosis.
- 04
Body fat alone isn't fitness
Strength, cardio, mobility, and sleep matter as much as composition. Body fat is one signal, not the goal.
05Loved by
Coaches, lifters, and returning athletes.
Onboarding clients who don't have access to calipers or DEXA. The Navy method gets us a reasonable baseline in two minutes.
Cut planning. Re-measure every two weeks, watch the trend, adjust calories. Easier to interpret than the scale alone.
Coming back from injury. Body fat estimate + BMI together resets expectations after months of low activity.
06Questions
Body fat, plainly answered.
Questions before your first measurement. Missing one? hello@wirelogs.com.
01How accurate is the U.S. Navy method?
Typically within 3–4 percentage points of a DEXA scan for adults with average body composition. Less accurate at extremes — very lean athletes and very high body fat percentages.
02Why does the formula differ for men and women?
Average body fat distribution differs by sex, particularly around the hips. The female formula adds hip circumference to account for this; the male formula does not.
03Do I need calipers?
No. The Navy method uses only a flexible tape measure — neck, waist, and (for women) hips.
04What's a 'good' body fat percentage?
Healthy adult men typically fall in 10–20%; healthy adult women fall in 18–28%. Athletes go lower; 'over fat' starts above ~25% (men) or 32% (women). Context matters — age and goals shift what's appropriate.
05Are my measurements sent anywhere?
No. Everything stays in your browser. Wirelogs never sees the numbers you type.
06Is it free?
Yes. No sign-up, no usage cap, no watermark.
Ready when you are
Estimate composition.
Enter your measurements above. Body fat percentage and category appear instantly.
- Navy methodwell-validated
- Localprivate
- $0now and always