Deficit

Body Fat Percentage Calculator (Navy + Skinfold)

Two ways to estimate body fat without a clinic: a tape measure (the U.S. Navy method) or a pair of calipers (Jackson-Pollock 3-site). Either one chains forward here into your fat mass, lean mass, and the calorie deficit that sets a cut, using the same math the Deficit app runs.

Calculate Your Body Fat

Sex
Units

Estimates only. Talk to a doctor or registered dietitian before acting on these numbers for medical reasons.

The sections below explain what body fat percentage is, how each method gets its number, and how accurate each one is.

What is body fat percentage?

Body fat percentage is the share of your total weight made of fat tissue. At 80 kg and 15% body fat, you carry 12 kg of fat and 68 kg of everything else: muscle, bone, organs, and water. That everything-else number is your lean body mass.

It answers a question the scale can't. Two people at the same weight and height can look and perform nothing alike, because one carries twice the fat of the other. Body fat percentage sees that gap; weight and BMI don't.

Body fat percentage vs BMI

BMI is weight divided by height squared. It never measures fat. A trained lifter and a sedentary person of the same height and weight share one BMI while sitting 15 percentage points apart on body fat. BMI screens populations; body fat percentage measures an individual.

Body fat percentage vs scale weight

Scale weight moves with water, glycogen, and food in transit, often by 1 to 2 kg inside a single day. Body fat changes slowly, over weeks. During a cut the scale can stall while body fat keeps dropping, which is the whole reason to track composition rather than weight alone. The scale weight vs body fat post covers why the two diverge.

How does this calculator work?

Both methods estimate body density or fat directly, then this page turns the result into fat mass, lean mass, and a recommended deficit. The how Deficit works page covers the math and the research behind each step.

The U.S. Navy method (tape measure)

The Navy method estimates body fat from circumferences: neck and waist for men, plus hips for women. It needs a flexible tape measure and nothing else. 

Men:   %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
Women: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387

All measurements in inches inside the formula; the calculator converts for you when you pick metric.

Jackson-Pollock 3-site (skinfold calipers)

Calipers measure the fat directly under the skin at three sites. The Jackson-Pollock equation converts the sum of those folds, plus your age, into body density, and the Siri equation converts density into body fat. Men pinch chest, abdomen, and thigh; women pinch triceps, suprailiac, and thigh. 

Men:   density = 1.10938 − 0.0008267×sum + 0.0000016×sum² − 0.0002574×age
Women: density = 1.0994921 − 0.0009929×sum + 0.0000023×sum² − 0.0001392×age
%BF    = 495 / density − 450   (Siri)

Body fat percentage categories

The same label lands at a different number for each sex, because women carry more essential fat (about 10 to 13%) than men (about 3 to 5%). These are the bands the calculator uses.

For men

Body fat %Category
under 8%Contest prep
8 to 15%Athletic
15 to 21%Average
21 to 26%Overweight
26% and upObese

For women

Body fat %Category
under 14%Contest prep
14 to 24%Athletic
24 to 33%Average
33 to 39%Overweight
39% and upObese

Contest prep is the leanest band, the level physique competitors hold for a stage. Almost nobody stays there year-round, because sitting at the floor for long stretches costs hormones and recovery.

How accurate is each method?

No at-home method is exact. For a cut, you need a number consistent enough that the change over weeks is real.

Method Accuracy Cost Notes
Navy tape ±3% Free Weakest under 8% or over 30% body fat
Skinfold (JP 3-site) ±3 to 4% $15 to $30 Needs practice and usually a partner
Smart scale (BIA) ±5% or worse $30 to $60 Trust the weekly trend, not the daily number
BodPod / hydrostatic ±2% $40 to $75 Lab visit, less common than DEXA
DEXA scan ±1% $50 to $100 Gold standard; worth it at a cycle's start and end

Bio-electrical impedance (the smart-scale method) sends a small current through the body and infers fat from resistance. Hydration throws it off by several points, so read the trend across weeks and ignore the absolute figure.

Which method should you use?

Pick one and stay with it. Switching methods mid-cut introduces a calibration gap that looks like progress or its opposite when nothing changed.

  • No gear, want a number now. Use the Navy method. It's free, takes two minutes, and tracks change well even when the absolute figure is a point or two off.
  • Have calipers and a steady hand (or a partner). Skinfolds measure fat directly rather than inferring it from circumferences, so they read truer in trained people once your technique settles.
  • Want a real baseline. Book a DEXA at the start of a cycle and another at the end. Two accurate points bracket the whole cut and tell you how much fat you lost versus lean mass you kept.

What should you do with your body fat number?

A body fat percentage on its own is trivia. It earns its place when it sets how lean you are right now, how aggressive a deficit you can run, and how much protein protects your muscle. That last one runs on lean mass, not bodyweight, which is the whole argument in how much protein on a cut. Your body fat number also feeds the Cunningham BMR estimate, the best BMR formula for athletes.

The calculator above turns your number into a recommended deficit by interpolating between body-fat anchor points, gentler when you're lean and steeper when you have more to lose. To carry it the rest of the way into calories, a daily protein target, and an 8-week plan, send it to the lean body mass calculator. If you only want maintenance calories, the TDEE calculator takes the same inputs.

Frequently Asked Questions

How accurate is the U.S. Navy body fat calculator?

Within about ±3% for typical body compositions (8 to 30% body fat). It loses accuracy below 8% or above 30%, because the formula was fitted on people in between. At the edges, calipers or a DEXA scan read truer.

Do I need my weight to use this calculator?

No. Body fat percentage comes from the measurements alone. Adding weight unlocks two extra numbers, fat mass and lean body mass, since both are a share of total weight.

Why do the skinfold sites change between men and women?

Men and women store fat differently, so the Jackson-Pollock equation uses sex-specific sites: chest, abdomen, and thigh for men; triceps, suprailiac, and thigh for women. The calculator swaps the labels when you change the sex setting.

Which is better, the Navy method or skinfolds?

Skinfolds measure fat directly and read truer in trained people once your technique is consistent, but they need calipers and practice. The Navy method needs only a tape measure and tracks change well. Either works; the one you'll repeat every few weeks wins.

How often should I remeasure?

Every four weeks. Body fat barely moves week to week, and remeasuring too often feeds noise. Measure under the same conditions each time: same tape or calipers, same hydration, same time of day.

Can smart-scale body fat be trusted?

Not the single reading. Bio-electrical impedance can miss by five points or more depending on hydration. The weekly trend is useful; the daily number isn't.

Sources

See it in the app

Deficit takes your body fat percentage and runs the cut from it, adjusting calories, protein, and remaining cycle days each week based on what your body does.

Try for free