Is BMI a good health measure?

It's a rough screening tool. It correlates with metabolic risk at the population level but can mislabel individuals. Waist-to-height ratio and body-fat percent are better individual measures.

Does BMI differ by ethnicity?

Yes. Risk thresholds are lower for people of South Asian ancestry (some guidelines use 23 as 'overweight' and 27.5 as 'obese'). Talk to a doctor for targets specific to you.

How is BMI calculated?

BMI = weight (kg) / height (m)^2. For imperial: BMI = (weight in lbs / height in inches^2) x 703. The formula was developed by Belgian statistician Adolphe Quetelet in the 1830s as a population-level measure (originally called the 'Quetelet Index'). The 'BMI' name was popularized in the 1970s by physiologist Ancel Keys. It was never designed for individual diagnosis — Quetelet himself emphasized population-level use.

What's a healthier alternative to BMI?

Waist-to-height ratio: keep waist circumference under half your height (e.g., 70 inches tall = waist under 35 inches). This metric better predicts metabolic syndrome and cardiovascular risk than BMI. Body-fat percentage: 10-20% for men, 18-28% for women is considered healthy. Waist-hip ratio under 0.9 (men) or 0.85 (women) reduces metabolic disease risk. DEXA scans, hydrostatic weighing, or 3D body scans give precise body-fat numbers but require specialized equipment.

What does it mean if my BMI is 'overweight' but I'm fit?

Common situation for muscular athletes. BMI doesn't distinguish muscle from fat — a 6-foot 200lb football player and a 6-foot 200lb sedentary office worker have the same BMI (27.1, 'overweight') but very different body compositions. If your waist-to-height ratio is below 0.5, your body-fat % is in the healthy range, and your blood markers (cholesterol, blood sugar, blood pressure) are normal, an 'overweight' BMI is essentially meaningless. Your doctor will likely confirm you're metabolically healthy.

Should children be measured with BMI?

Use pediatric BMI percentiles, not adult categories. Children's BMI is plotted on age and sex-specific growth charts (CDC for US, WHO for international). 5th-85th percentile is healthy weight; 85th-95th is overweight; 95th+ is obese. The same absolute BMI number means very different things at different ages because children's body composition changes with growth. Adult BMI categories (18.5-24.9 = normal) don't apply until age 18+. Pediatricians track BMI percentile trajectories at well-child visits.

Is this BMI calculator accurate for my body type?

The math (kg/m² or lb/in²×703) is exact. Whether the OUTPUT is meaningful for you depends on body composition and ancestry. BMI is reasonably useful as a population screening tool for sedentary adults of European descent aged 25-65. It's misleading for: (1) Athletes and lifters (high muscle mass falsely flags as overweight). (2) People of Asian descent (lower disease-risk thresholds — 23 'overweight', 27.5 'obese' per WHO Asian guidelines). (3) Older adults (sarcopenic obesity — low muscle, normal BMI). (4) Tall people (BMI math under-states in heights >6'2). (5) Children (use percentile-based pediatric growth charts). For most accurate read on health status, supplement with waist-to-height ratio (under 0.5 healthy), body-fat % (DEXA scan or BIA scale), and metabolic markers (fasting glucose, A1C, lipids).

How do I calculate BMI manually with imperial units?

Formula: BMI = (weight in pounds / height in inches²) × 703. Example: 170 lb, 5'10' (70 inches). 170 / (70²) = 170 / 4900 = 0.0347. 0.0347 × 703 = 24.4. Result: 24.4 BMI (normal weight, just under the 25 overweight threshold). Why 703? It's the unit conversion factor: BMI was defined in metric (kg/m²); 703 converts pounds and inches to roughly the same scale. Categories: under 18.5 underweight; 18.5-24.9 normal; 25-29.9 overweight; 30+ obese (with class I 30-34.9, class II 35-39.9, class III 40+). Mental shortcut for 'am I above 25?': pounds × 703 / inches² > 25 simplifies roughly to pounds > 0.0356 × inches². At 70 inches: above 174 lb is overweight. At 72 inches: above 184 lb. At 65 inches: above 150 lb.

What's the best body composition tool besides BMI?

Ranked by accuracy: (1) DEXA scan (gold standard) — $75-200 at imaging centers and many gyms, returns body-fat %, lean mass, bone density, regional fat distribution. Most accurate. (2) Hydrostatic weighing (underwater) — second most accurate but rare and uncomfortable. (3) Bod Pod (air displacement) — comparable to DEXA, $50-100. (4) BIA scales (Withings, Tanita, Omron) — $30-300 home scales, send small electrical current through body to estimate fat %. Accuracy varies 2-5% depending on hydration, recent meals, exercise. (5) Skinfold calipers — $10-30, requires a trained tester. (6) Tape-measure ratios — waist-to-height (keep waist under half your height), waist-to-hip (men under 0.9, women under 0.85). Free and surprisingly predictive of metabolic risk. Most cost-effective combo: home BIA scale weekly + tape-measure waist monthly + occasional DEXA scan (annually) for ground truth.

Health & Fitness · Free tool

BMI Calculator

Input your height and weight to see your BMI score and health category online. Understand your result in plain English with this free calculator.

Updated June 2026

Height (cm)Weight (kg)

Your BMI

23.5

Normal weight

WHO BMI ranges

Underweight: < 18.5
Normal: 18.5 – 24.9
Overweight: 25.0 – 29.9
Obese: 30.0+

BMI is a rough screen, not a diagnosis. Muscle mass and body composition matter.

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What it does

A free BMI (body mass index) calculator that takes metric or imperial inputs and returns your BMI plus the WHO classification: underweight, normal, overweight, or obese. Runs in your browser with no tracking.

BMI is a rough screening tool, not a diagnosis. It doesn’t account for muscle mass, frame size, or body composition — a lean athlete can register as “overweight” on BMI while being in peak health. Use it as one data point among several, not as the defining measure of fitness.

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Example input & output

Input

Height: 175 cm
Weight: 72 kg

Output

BMI: 23.5
Category: Normal (WHO 18.5–24.9)

WHO categories: under 18.5 underweight; 18.5–24.9 normal; 25–29.9 overweight; 30+ obese.

How to use it

Pick metric (cm / kg) or imperial (ft, in / lb).
Enter your height and weight.
Read your BMI and the WHO category it falls in.
Treat it as a screening number, not a verdict.

How it works

Key takeaways

BMI was designed in 1832 by Adolphe Quetelet as a population statistic — its inventor explicitly warned it was not for individual diagnosis.
BMI can’t tell muscle from fat. A 6-ft 200-lb football player and a 6-ft 200-lb sedentary worker both register BMI 27.1 (“overweight”).
Waist-to-height ratio under 0.5 (waist less than half your height) predicts metabolic and cardiovascular risk better than BMI does.
South Asian populations hit metabolic-disease risk at lower BMI than European populations — some guidelines use 23 as “overweight” and 27.5 as “obese” for South Asian patients.

Metric: BMI = weight (kg) / height (m)². Imperial: BMI = (lb / in²) × 703. The formula dates to Adolphe Quetelet in 1832 as a population statistic; it was named “BMI” by Ancel Keys in 1972. Quetelet himself emphasized it was a population-level measure, not for individual diagnosis.

Advanced: why BMI mis-classifies athletes and ethnic groups

BMI doesn’t distinguish muscle from fat. Two 6-foot, 200-lb people — a football player and a sedentary office worker — both register BMI 27.1 (“overweight”). For lean-muscular populations (rugby, weightlifting, gymnastics), BMI is essentially meaningless. Ethnicity-specific thresholds matter too: people of South Asian ancestry hit metabolic-disease risk at lower BMI than European-descent populations — some guidelines use BMI 23 as “overweight” and 27.5 as “obese” for South Asian patients. The WHO categories were calibrated against European/American populations.

How this compares to alternatives

vs waist-to-height ratio: keep waist under half your height (e.g., 70 inches tall → waist under 35 inches). Better predictor of metabolic syndrome than BMI. vs body-fat percentage: 10-20% for men, 18-28% for women is healthy. Methods: DEXA scan ($75-200, gold standard), bioelectric impedance scales ($30-150, less accurate), calipers (free if you have one, requires practice). vs blood markers: cholesterol, fasting glucose, A1C, blood pressure tell more about metabolic health than BMI. See the BMI glossary for the formal definition.

Common mistakes when using this tool

Treating BMI as diagnosis. It’s a screening tool. Doctors who care about your individual health look at body composition, blood markers, family history, and lifestyle — not BMI alone.
Using adult BMI for kids. Pediatric BMI uses age- and sex-specific growth-curve percentiles, not the 18.5-24.9 adult range.
Ignoring ethnic-group adjustments. South Asian populations have lower thresholds (23 / 27.5). Don’t use one-size-fits-all categories.
Tracking BMI day-to-day. Body weight fluctuates 1-3% daily on water, sodium, hormones. Track weekly average over months, not single-day BMI.

Learn more about body-composition metrics

BMI limitations — the 6 specific populations BMI mis-classifies, with the metabolic-health markers to use instead.
Waist-to-height ratio — the “keep your waist under half your height” rule and why it beats BMI for cardiovascular risk prediction.
Body-fat percentage — healthy ranges by age and sex, plus a comparison of measurement methods (DEXA, BIA, calipers).
Resting metabolic rate — the calories your body burns at rest and how it relates to body composition.

When to use this tool

You want the number WHO uses, for screening purposes only.
You're tracking your own trend over time.

When not to use it

You're muscular or athletic — BMI will classify you as overweight when you're lean. Use body-fat percent or waist-to-height ratio instead.
You're under 18 — use a pediatric BMI percentile calculator, not an adult one.
You're pregnant — BMI doesn't apply.

Common use cases

Quick check against a doctor's BMI number.
Tracking a rough trend over months while losing or gaining weight.
Filling a field on a form that asks for BMI.

Frequently asked questions

Is BMI a good health measure?: It's a rough screening tool. It correlates with metabolic risk at the population level but can mislabel individuals. Waist-to-height ratio and body-fat percent are better individual measures.
Does BMI differ by ethnicity?: Yes. Risk thresholds are lower for people of South Asian ancestry (some guidelines use 23 as 'overweight' and 27.5 as 'obese'). Talk to a doctor for targets specific to you.
How is BMI calculated?: BMI = weight (kg) / height (m)^2. For imperial: BMI = (weight in lbs / height in inches^2) x 703. The formula was developed by Belgian statistician Adolphe Quetelet in the 1830s as a population-level measure (originally called the 'Quetelet Index'). The 'BMI' name was popularized in the 1970s by physiologist Ancel Keys. It was never designed for individual diagnosis — Quetelet himself emphasized population-level use.
What's a healthier alternative to BMI?: Waist-to-height ratio: keep waist circumference under half your height (e.g., 70 inches tall = waist under 35 inches). This metric better predicts metabolic syndrome and cardiovascular risk than BMI. Body-fat percentage: 10-20% for men, 18-28% for women is considered healthy. Waist-hip ratio under 0.9 (men) or 0.85 (women) reduces metabolic disease risk. DEXA scans, hydrostatic weighing, or 3D body scans give precise body-fat numbers but require specialized equipment.
What does it mean if my BMI is 'overweight' but I'm fit?: Common situation for muscular athletes. BMI doesn't distinguish muscle from fat — a 6-foot 200lb football player and a 6-foot 200lb sedentary office worker have the same BMI (27.1, 'overweight') but very different body compositions. If your waist-to-height ratio is below 0.5, your body-fat % is in the healthy range, and your blood markers (cholesterol, blood sugar, blood pressure) are normal, an 'overweight' BMI is essentially meaningless. Your doctor will likely confirm you're metabolically healthy.
Should children be measured with BMI?: Use pediatric BMI percentiles, not adult categories. Children's BMI is plotted on age and sex-specific growth charts (CDC for US, WHO for international). 5th-85th percentile is healthy weight; 85th-95th is overweight; 95th+ is obese. The same absolute BMI number means very different things at different ages because children's body composition changes with growth. Adult BMI categories (18.5-24.9 = normal) don't apply until age 18+. Pediatricians track BMI percentile trajectories at well-child visits.
Is this BMI calculator accurate for my body type?: The math (kg/m² or lb/in²×703) is exact. Whether the OUTPUT is meaningful for you depends on body composition and ancestry. BMI is reasonably useful as a population screening tool for sedentary adults of European descent aged 25-65. It's misleading for: (1) Athletes and lifters (high muscle mass falsely flags as overweight). (2) People of Asian descent (lower disease-risk thresholds — 23 'overweight', 27.5 'obese' per WHO Asian guidelines). (3) Older adults (sarcopenic obesity — low muscle, normal BMI). (4) Tall people (BMI math under-states in heights >6'2). (5) Children (use percentile-based pediatric growth charts). For most accurate read on health status, supplement with waist-to-height ratio (under 0.5 healthy), body-fat % (DEXA scan or BIA scale), and metabolic markers (fasting glucose, A1C, lipids).
How do I calculate BMI manually with imperial units?: Formula: BMI = (weight in pounds / height in inches²) × 703. Example: 170 lb, 5'10' (70 inches). 170 / (70²) = 170 / 4900 = 0.0347. 0.0347 × 703 = 24.4. Result: 24.4 BMI (normal weight, just under the 25 overweight threshold). Why 703? It's the unit conversion factor: BMI was defined in metric (kg/m²); 703 converts pounds and inches to roughly the same scale. Categories: under 18.5 underweight; 18.5-24.9 normal; 25-29.9 overweight; 30+ obese (with class I 30-34.9, class II 35-39.9, class III 40+). Mental shortcut for 'am I above 25?': pounds × 703 / inches² > 25 simplifies roughly to pounds > 0.0356 × inches². At 70 inches: above 174 lb is overweight. At 72 inches: above 184 lb. At 65 inches: above 150 lb.
What's the best body composition tool besides BMI?: Ranked by accuracy: (1) DEXA scan (gold standard) — $75-200 at imaging centers and many gyms, returns body-fat %, lean mass, bone density, regional fat distribution. Most accurate. (2) Hydrostatic weighing (underwater) — second most accurate but rare and uncomfortable. (3) Bod Pod (air displacement) — comparable to DEXA, $50-100. (4) BIA scales (Withings, Tanita, Omron) — $30-300 home scales, send small electrical current through body to estimate fat %. Accuracy varies 2-5% depending on hydration, recent meals, exercise. (5) Skinfold calipers — $10-30, requires a trained tester. (6) Tape-measure ratios — waist-to-height (keep waist under half your height), waist-to-hip (men under 0.9, women under 0.85). Free and surprisingly predictive of metabolic risk. Most cost-effective combo: home BIA scale weekly + tape-measure waist monthly + occasional DEXA scan (annually) for ground truth.

Show the math + sources

Formula

BMI = weight (kg) ÷ height (m)². CDC adult categories: <18.5 underweight, 18.5–24.9 healthy, 25.0–29.9 overweight, ≥30.0 obese.

What this assumes

Adults 20+ years old, not pregnant. BMI is a population-level screening number, not a measure of body fat or health on its own. Athletes with high muscle mass and very tall/short adults often score outside their actual body composition.

Sources

CDC — Adult BMI Categories

Methodology last verified: 2026-04-30

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