Body Fat Percentage Calculator

Percent body fat equals total weight minus lean mass divided by total weight times 100

Solution

—
Share:

How It Works

Body fat percentage from lean body mass and total weight uses the simple identity: BF% = (W − LBM) / W × 100, where W is your total body weight and LBM is your lean body mass (everything that isn't fat — muscle, bone, water, organs). This page does NOT derive lean mass from skinfold calipers or DEXA scans; you must provide it. If you have a DEXA, BodPod, or hydrostatic measurement of lean mass, this calculator converts the relationship into a percentage with the work shown.

Example Problem

An athlete weighs 70 kg total. A DEXA scan reports 55 kg of lean body mass. What is the body fat percentage?

  1. Use the formula: BF% = (W − LBM) / W × 100.
  2. Substitute: BF% = (70 − 55) / 70 × 100.
  3. Subtract: 70 − 55 = 15.
  4. Divide: 15 / 70 ≈ 0.2143.
  5. Multiply by 100: 0.2143 × 100 ≈ 21.4%.

Key Concepts

Body fat percentage is a better health indicator than BMI for athletes and people with high muscle mass, but it requires an actual measurement of lean body mass — not an estimate. Common measurement methods (most → least accurate): hydrostatic weighing, DEXA, BodPod (air displacement), bioelectrical impedance, skinfold calipers (3- or 7-site Jackson-Pollock equations). Each has a margin of error: DEXA ±1-2%, skinfolds ±3-5% in trained hands, consumer scales using bioimpedance ±4-8%. American Council on Exercise (ACE) classifications: essential fat 10-13% (women) / 2-5% (men), athletes 14-20% / 6-13%, fitness 21-24% / 14-17%, average 25-31% / 18-24%, obese 32%+ / 25%+.

Applications

  • Tracking body composition changes during a cut or recomposition phase.
  • Calibrating sports performance training to lean mass rather than total weight.
  • Clinical screening for sarcopenic obesity (low lean mass + high body fat).
  • Setting realistic physique goals (a body fat target is more meaningful than a scale weight).
  • Cross-checking BMI in muscular populations where BMI overestimates body-fat risk.

Common Mistakes

  • Treating a consumer bathroom scale's body-fat reading as ground truth. Bioimpedance is heavily affected by hydration; ±5% variability across a day is common.
  • Using skinfold-based body fat without proper training in caliper technique. Even small site-location errors compound across the 3-site or 7-site equations.
  • Confusing body fat percentage with BMI. BMI is a ratio of mass to height; body fat is a ratio of fat mass to total mass. They correlate but measure different things.
  • Aiming for 'essential fat' levels (10-13% women, 2-5% men) for general health. These are short-duration competition values; sustaining them is unhealthy.
  • Forgetting that lean body mass and total weight must be in the same unit. This calculator uses a single shared mass-unit selector so the two inputs cannot diverge.

Frequently Asked Questions

How do you calculate body fat percentage?

If you know your total weight (W) and lean body mass (LBM, the non-fat tissue): BF% = (W − LBM) / W × 100. Example: 70 kg total, 55 kg lean → BF% = (70 − 55) / 70 × 100 ≈ 21.4%.

What is the formula for body fat percentage?

BF% = (Total Weight − Lean Body Mass) ÷ Total Weight × 100. The formula assumes you know your lean body mass from a separate measurement (DEXA, BodPod, hydrostatic, or skinfold).

What's a healthy body fat percentage?

American Council on Exercise classifications for adults: Athletes 14-20% (women) / 6-13% (men); Fitness 21-24% / 14-17%; Average 25-31% / 18-24%; Obese 32%+ / 25%+. Below 'essential fat' (10-13% women / 2-5% men) is unhealthy long-term.

How accurate is bioelectrical impedance body fat?

Consumer bathroom scales using bioimpedance have ±4-8% error and are sensitive to hydration, food intake, and time of day. They're useful for tracking trends if you measure under consistent conditions, but a single reading shouldn't be treated as ground truth.

Is body fat percentage better than BMI?

For athletes, muscular individuals, and anyone where BMI gives a misleading classification, yes. Body fat percentage measures what BMI is trying to proxy. But BMI is cheaper and faster — no measurement needed — so it remains the standard population-level screen.

Where do I get my lean body mass measurement?

DEXA scans (most accurate, ~$50-150 at sports medicine clinics), BodPod air displacement plethysmography, hydrostatic underwater weighing, professional skinfold caliper measurements by a trained technician (Jackson-Pollock 3-site or 7-site protocol), or consumer-grade bioimpedance scales (least accurate but cheapest).

Worked Examples

Bodybuilding Pre-Show

What body fat percentage does a male bodybuilder hit before a show?

A natural male bodybuilder weighs 88 kg in the final week of his cutting cycle. A DEXA scan reports 81 kg of lean body mass. What is his current body fat percentage?

  • Knowns: total weight W = 88 kg, lean body mass LBM = 81 kg.
  • Apply the formula: %Fat = (W − LBM) / W × 100.
  • Substitute: %Fat = (88 − 81) / 88 × 100.
  • Subtract first: 88 − 81 = 7.
  • Divide and scale: 7 / 88 × 100 ≈ 7.95 ≈ 8.0.

Body Fat ≈ 8.0%

Competition-stage body fat for male physique athletes typically lands in the 4–7% range. ACE classifies 6–13% as 'Athletes' for men; below 5% is considered too low to sustain outside of show week.

Postpartum Health

What is a typical postpartum body fat percentage at 12 weeks?

A woman 12 weeks postpartum weighs 72 kg. A clinical skinfold-protocol estimate gives her lean body mass at 50 kg. What does the body fat percentage work out to?

  • Knowns: total weight W = 72 kg, lean body mass LBM = 50 kg.
  • Apply the formula: %Fat = (W − LBM) / W × 100.
  • Substitute: %Fat = (72 − 50) / 72 × 100.
  • Subtract first: 72 − 50 = 22.
  • Divide and scale: 22 / 72 × 100 ≈ 30.6.

Body Fat ≈ 30.6%

Informational only — not a substitute for clinical judgment. Postpartum body composition changes over the first year; the ACE 'Acceptable' band for women is 25–31%, and gradual return toward pre-pregnancy levels is normal at this stage.

Endurance Sports

What body fat percentage does a female triathlete carry in season?

A female triathlete weighs 60 kg in race season. A BodPod scan reports 49 kg of lean body mass. What is her body fat percentage relative to the ACE chart?

  • Knowns: total weight W = 60 kg, lean body mass LBM = 49 kg.
  • Apply the formula: %Fat = (W − LBM) / W × 100.
  • Substitute: %Fat = (60 − 49) / 60 × 100.
  • Subtract first: 60 − 49 = 11.
  • Divide and scale: 11 / 60 × 100 ≈ 18.3.

Body Fat ≈ 18.3%

ACE classifies 14–20% as the 'Athletes' range for women. Endurance athletes who drop too far below this can disrupt menstrual cycles (RED-S / Female Athlete Triad) — sustained body fat under ~12% in adult women is a clinical concern.

Body Fat Percentage Formula

Body fat percentage is the fraction of total body mass made up of adipose tissue. Given total weight and an independent estimate of lean body mass (from DXA, hydrostatic weighing, BIA, skinfold callipers, or a body-composition scan), body fat percentage is the simple subtraction-and-divide:

%Fat = (W − LBM) / W × 100Two-compartment model (fat mass ÷ total mass)

Where:

  • %Fat — body fat percentage (unitless, expressed as %)
  • W — total body weight (kg or lb — both sides cancel, so units don't need conversion as long as W and LBM use the same unit)
  • LBM — lean body mass: everything that isn't fat (muscle, bone, organs, body water, connective tissue)

Accuracy depends entirely on the lean-mass measurement. DXA and hydrostatic weighing are the research gold standards (±1–2% absolute error); BIA scales and seven-site skinfolds are typically ±3–5%; most consumer wrist-worn devices are not validated for body composition. The two-compartment model also assumes a fixed density for lean tissue, which can mis-estimate athletes (high bone density), pregnant women, and people with significant edema. ACE classifies adult men as healthy at roughly 14–24% body fat and adult women at roughly 21–31%; sustained values well below the athlete range (under ~6% for men, ~12% for women) are associated with hormonal and reproductive risks. This calculator is informational only and is not a substitute for clinical judgment.

Body Fat Percentage Categories (ACE)

The American Council on Exercise (ACE) groups body fat percentage into five descriptive bands, with separate ranges for women and men. Use the column that matches the person being measured; these are general reference ranges, not diagnostic thresholds.

CategoryWomen (%)Men (%)
Essential fat10–13%2–5%
Athletes14–20%6–13%
Fitness21–24%14–17%
Average / Acceptable25–31%18–24%
Obese32%+25%+

Source: American Council on Exercise (ACE) body composition categories. Ranges are general references and vary with age and measurement method; this calculator is informational only and is not a substitute for clinical judgment.

Related Calculators

Related Sites