Health & Life Runs locally Ready to use Built-in examples No tracking

Body Fat Calculator

Estimate body fat percentage with the Deurenberg formula and classify by sex-specific thresholds.

Two people of the same height and weight — one lifting regularly, one sitting all day — can share a BMI exactly, and for telling whether someone is carrying too much fat, body-fat percentage says more. Enter the four basic measurements for a formula-based estimate, classified in five levels against the ACE thresholds; a formula is a population statistic, so being three or five points out is normal, and the trend matters more than the number.

A statement on accuracy: the formula is an estimate, a regression over a population, and for one individual the error can reach three to five percentage points; it overestimates the heavily muscled and underestimates older people and those with low bone density. Precise measurement wants calipers, bioelectrical impedance or a DEXA scan — this tool suits tracking a trend from day to day.

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How to use

  1. Enter age, sex, height and weight.
  2. Read the estimated body-fat percentage and its category.
  3. Compare against the ACE thresholds shown.
  4. Track the trend rather than chasing the exact number.

How it works

How to enter data

Pick your sex and enter age, height (cm) and weight (kg).

Body-fat classification standard

Press "calculate" for the estimated body-fat percentage and classification; classification uses different thresholds by sex: men underweight < 6%, athlete < 14%, healthy < 18%, acceptable < 25%, high at 25% and above; women 14% / 18% / 25% / 32% respectively.

Body fat vs. BMI

Body fat differs from BMI: it distinguishes muscle from fat. Gym-goers may have an "overweight" BMI but healthy body fat — judge leanness by body fat.

Code example

JavaScript The Deurenberg formula 

function bodyFat(hCm, wKg, age, male) {
  const bmi = wKg / (hCm / 100) ** 2;
  const sex = male ? 1 : 0;
  return 1.2 * bmi + 0.23 * age - 10.8 * sex - 5.4;
}

// Healthy ranges are roughly 14~24% for men and 21~31% for women (ACE reference)
// A formula is only an estimate; individual error is 3~5 percentage points
bodyFat(175, 75, 30, true);   // ≈ 20.4%

Python The same formula in Python 

def body_fat(h_cm, w_kg, age, male):
    bmi = w_kg / (h_cm / 100) ** 2
    return 1.2 * bmi + 0.23 * age - 10.8 * (1 if male else 0) - 5.4

body_fat(175, 75, 30, True)   # ≈ 20.4

# ACE bands: low / athlete / healthy / acceptable / high
# Thresholds differ by sex, and the formula overestimates athletic builds

FAQ

How does body-fat percentage differ from BMI?

BMI uses only height and weight and can't separate muscle from fat — muscle is dense, so gym-goers are often misjudged as overweight. Body-fat percentage directly estimates the fat share, better reflecting true obesity. Look at both for accuracy.

Why is women's healthy body fat higher than men's?

Physiology: women need to maintain reproductive function, and essential fat (about 10-13%) is far above men's (about 2-5%). So the same body-fat figure has a completely different health standard by sex — this tool switches thresholds automatically by sex.

Is the estimate accurate?

Deurenberg is a population-statistics formula, within about +/-3-4% for most adults, but with larger errors for pregnant women, children, professional athletes and those with abnormal muscle mass. For precise values, use DEXA (dual-energy X-ray) or a bioimpedance scale.

What body-fat percentage is normal?

Per ACE reference ranges: men athlete 6-13%, healthy 14-17%, acceptable 18-24%, high at 25%+; women athlete 14-20%, healthy 21-24%, acceptable 25-31%, high at 32%+. Individual variation is large, so a range is more meaningful than a single number.

How do I lower my body-fat percentage?

The core is a calorie deficit plus strength training: keep a 300-500 kcal daily deficit, ensure about 1.6 g of protein per kg of body weight, do strength training 2-3 times a week to preserve muscle, plus moderate cardio. Rapid dieting loses muscle and water first and rebounds easily.

Is lower body fat always better?

No. Men below 5% and women below 12% long-term may affect hormone secretion, immune function and the menstrual cycle — an unhealthy range. Fat participates in hormone synthesis and organ protection, so the goal should be a healthy range, not the lowest number.

Is a home body-fat scale accurate?

Home scales use bioelectrical impedance, heavily affected by hydration, eating and exercise state; repeated tests at the same time can vary 2-5%. It's better for observing long-term trends (like monthly change) than absolute values; measure at a fixed time and body state.

Are my body measurements collected?

No. Height, weight and waist data are used only in local formulas, not uploaded to a server; we have no collection endpoint and do no user identification. History stays in your browser, erasable with "clear," and incognito mode fully avoids a trace.