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BMI from height & weight

BMI Calculator

Calculate your Body Mass Index based on height and weight.

By Jeff Beem

Updated

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01

Inputs

For ages 2–19, used with sex for percentile (approximate).

175 cm
100175250
70 kg
30115200

For waist-to-height ratio when entered.

22.86BMI

Screening index only, not body fat or fitness.

WHO band: Healthy Weight

Population-level association with healthy weight; individuals vary.

Reference weight (BMI 18.5–24.9)

57–76 kg

Illustrative range for your height.

Spectrum (15–40)

Bands are population-level labels, not a diagnosis.

22.86
<18.518.5–24.925–29.9≥30

Signal strength (educational)

Waist-to-height

Often tracks central adiposity more closely than BMI alone.

BMI

Useful for populations; weaker for very muscular or some older adults.

Weight alone

Limited without height and composition context.

Informational only, not medical advice. Discuss results with a qualified clinician.

When BMI gets it wrong

BMI was developed in the 1830s by Adolphe Quetelet as a population-statistics tool, not a clinical diagnostic, and the design choice still shows. The formula trades accuracy for arithmetic you can do in your head, which is why public-health agencies still use it and why it routinely mis-classifies athletes, adults over 65, and people with above-average muscle mass.

Why BMI is still everywhere

It needs only height and weight, both cheap to measure at scale. CDC, WHO, and most large cohort studies still rely on it for tracking trends across millions of people, even though everyone in the field acknowledges its individual-level limits. The formula was never meant to diagnose anyone; it was meant to describe populations.

Where BMI breaks down

Three groups regularly get mis-classified: athletes and others with high muscle mass, adults over 65 (where a 25–27 BMI tracks with lower frailty risk in several large cohort studies), and South and East Asian populations, who develop type 2 diabetes and cardiovascular risk at lower BMIs than the WHO chart anticipates. The WHO actually publishes a separate Asian-specific cutoff: overweight starts at 23 instead of 25, and obese at 27.5 instead of 30.

The athlete problem

A 5'10", 200 lb adult comes in at BMI 28.7, technically "overweight." If body fat is 9%, the range you'd find in a fit defensive back or a competitive natural bodybuilder, the health implications differ enormously from a sedentary adult at the same height and weight. BMI cannot make that distinction. For active individuals, body composition methods (DEXA, BodPod, even bioimpedance) are the more honest read.

After 65, a higher BMI may be protective

The reason is sarcopenia: age-related muscle loss makes a slightly higher BMI a marker for preserved lean mass and adequate nutrition rather than excess fat. Standard adult cutoffs treat the 70-year-old who has held onto muscle the same as the 70-year-old who has gained 30 pounds of body fat, and the two situations have opposite implications for frailty and mortality risk.

Waist-to-height often beats BMI

Waist-to-height ratio (WHtR) measures abdominal fat directly, which is what drives cardiometabolic risk most strongly. The simple version: keep your waist to less than half your height. For a 5'10" person, that's a 35-inch waist or smaller. The Ashwell meta-analyses since the early 2010s consistently find WHtR a stronger predictor of cardiovascular disease, type 2 diabetes, and metabolic syndrome than BMI alone, and the arithmetic is no harder.

What is BMI?

BMI (Body Mass Index) is a population-level screening metric that uses height and weight to provide a standardized risk signal. It's calculated using a simple formula that allows comparison across different heights. BMI reflects weight relative to height and does not measure body fat, fitness, or metabolic health.

The standard formula

BMI = kg/m²

Where kg is weight in kilograms and m² is height in meters squared. For example, a person who is 70 kg and 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.

How to interpret BMI results

BMI categories are population-level references based on statistical associations with health outcomes. Individual health varies significantly, and BMI is one signal among several that should be considered together.

BMI category (WHO reference) BMI range Population-level association
Underweight< 18.5May be associated with nutritional concerns at the population level
Reference range18.5 – 24.9Generally associated with lower health risk signals at the population level
Overweight25.0 – 29.9May correlate with higher health risk at the population level
Obese (class 1)30.0 – 34.9Correlates with higher health risk signals at the population level
Obese (class 2)35.0 – 39.9Correlates with significantly higher health risk signals at the population level
Obese (class 3)≥ 40.0Correlates with highest health risk signals at the population level

Note: These ranges are population-level references based on statistical associations. They may not apply to athletes, seniors, or individuals with high muscle mass. BMI does not directly measure body fat or account for muscle mass, bone density, or fat distribution. Individual health varies significantly.

BMI Calculator: Understanding Population-Level Risk Signals

A 5'10", 200 lb adult has a BMI of 28.7, which the chart labels "overweight." Same person with a 36-inch waist has a waist-to-height ratio of 0.51, just past the 0.5 threshold. The two numbers together say more than either says alone.

What This Calculator Does

Computes BMI from height and weight, classifying the result into the standard WHO/CDC bands (Underweight under 18.5, Healthy Weight 18.5–24.9, Overweight 25–29.9, Obese Classes 1 through 3 from 30 up). With an optional waist circumference, it also returns the waist-to-height ratio, which most cardiometabolic studies find is a stronger risk signal than BMI alone. BMI cannot tell muscle from fat, which is why a 5'10", 200 lb athletic adult lands at 28.7 (overweight by the chart) despite low body fat. For children and teens (ages 2–19), interpret BMI via CDC/WHO growth-chart percentiles rather than fixed thresholds. Treat the result as a screening number, not a diagnosis.

Understanding BMI Categories

The formula

  • BMI:
    BMI=weight (kg)height (m)2\text{BMI} = \frac{\text{weight (kg)}}{\text{height (m)}^2}

    For imperial units: BMI = (weight in lbs × 703) ÷ height (in)². The 703 conversion factor folds together the kg-to-lb and m-to-in unit conversions, so the imperial version returns the same number as the metric version for the same person. A 5'10", 200 lb adult: 200 × 703 / 70² = 28.7.

Adult BMI Categories (Ages 20+)

  • Underweight:
    BMI below 18.5
  • Healthy Weight:
    BMI 18.5 to 24.9
  • Overweight:
    BMI 25.0 to 29.9
  • Obese (Class 1):
    BMI 30.0 to 34.9
  • Obese (Class 2):
    BMI 35.0 to 39.9
  • Obese (Class 3):
    BMI 40.0 or higher

These ranges are population-level cutoffs based on observed mortality and morbidity associations, not individual diagnostic thresholds. They were calibrated largely on European-ancestry populations; the WHO publishes separate Asian-specific cutoffs (overweight at 23, obese at 27.5) because South and East Asian populations show metabolic risk at lower BMIs.

Child and Teen BMI (Ages 2–19)

  • Underweight:
    BMI percentile below 5th
  • Healthy Weight:
    BMI percentile 5th to 85th
  • Overweight:
    BMI percentile 85th to 95th
  • Obese:
    BMI percentile above 95th

Children and teens use CDC/WHO growth charts that compare BMI to others of the same age and sex, expressed as a percentile.

Why BMI is limited

BMI does not measure body fat

  • Muscle vs. fat:
    BMI treats them identically. A 5'10", 200 lb athletic adult lands at 28.7 (overweight by the chart) with single-digit body fat. A sedentary adult at the same height and weight has a very different metabolic profile, but their BMI is the same number.
  • Where the fat sits:
    Abdominal (visceral) fat tracks much more strongly with cardiometabolic disease than subcutaneous fat on hips and thighs. BMI knows nothing about distribution. Two adults with identical BMI and identical body-fat percentage can have very different cardiovascular risk profiles depending on whether the fat is around their organs or under their skin.

What works better

  • Waist-to-height ratio:
    Tape your waist (at the navel, breathing normally) and divide by your height. Under 0.5 is the population-level low-risk band; 0.5 or above starts pulling cardiometabolic risk numbers up. The arithmetic is no harder than BMI and the signal is stronger.
  • Body composition:
    DEXA gives the most accurate fat/lean/bone breakdown but requires a clinic visit. BodPod is comparable in accuracy. Skinfold calipers are cheap and reasonably accurate when used by someone trained. Consumer bioimpedance scales drift with hydration but track changes over time well enough.
  • Blood markers:
    Fasting glucose, HbA1c, lipid panel, and blood pressure speak more directly to cardiovascular and metabolic risk than BMI. They cost a fraction of a body-composition scan, and the signal is far less ambiguous.

BMI Calculator FAQ

What is BMI and how is it calculated?

BMI (Body Mass Index) is calculated using the formula: weight in kilograms divided by height in meters squared (kg/m²). For example, a person who is 70 kg and 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. BMI provides a simple screening tool for weight categories, but it does not directly measure body fat or account for muscle mass, bone density, or fat distribution.

Why is BMI limited as a health indicator?

BMI ignores several important factors: bone density, muscle mass, and fat distribution. Athletes with high muscle mass may have a high BMI despite low body fat. Seniors may have a higher BMI due to age-related muscle loss, but a BMI of 25–27 may actually be protective against frailty. Waist-to-height ratio is often a more accurate predictor of health risks than BMI alone.

How is BMI different for children and teens?

For children and teens (ages 2–19), BMI is calculated the same way but interpreted using CDC/WHO growth charts that compare the child's BMI to others of the same age and sex. The result is expressed as a percentile. A BMI percentile below 5th is underweight, 5th to 85th is healthy weight, 85th to 95th is overweight, and above 95th is obese.

What is a healthy BMI range for adults?

For adults 20 and older, a BMI between 18.5 and 24.9 is associated with lower health risk at the population level. Below 18.5 is underweight, 25.0 to 29.9 is overweight, and 30.0 or higher is obese (with Class 1: 30–34.9, Class 2: 35–39.9, Class 3: 40+). However, these ranges are population-level references and may not apply to athletes, seniors, or individuals with high muscle mass. Individual health varies significantly.

What is waist-to-height ratio and why does it matter?

Waist-to-height ratio (WHtR) is calculated by dividing waist circumference by height. A ratio below 0.5 is associated with lower cardiometabolic risk at the population level; 0.5 or above correlates with higher risk. The Ashwell meta-analyses since the early 2010s consistently find WHtR a stronger predictor of cardiovascular disease, type 2 diabetes, and metabolic syndrome than BMI alone, because waist circumference captures abdominal (visceral) fat directly. The simple rule: keep your waist to less than half your height. For a 5'10" person, that's a 35-inch waist or smaller.

Should seniors use the same BMI ranges?

For adults 65 and older, slightly higher BMI ranges may be appropriate. A BMI of 25–27 may be protective against frailty and mortality in older adults. Muscle loss (sarcopenia) is common with aging, so a slightly higher BMI can indicate better muscle mass and nutritional status. However, individual health factors should always be considered.

Why might athletes have a high BMI?

Athletes often have high muscle mass, which increases weight without increasing body fat. BMI does not distinguish between muscle and fat, so a muscular athlete may have a BMI in the "overweight" or even "obese" range despite having low body fat percentage. For athletes, body composition analysis (DEXA scan, bioimpedance) provides more accurate health assessment than BMI alone.

Sources & citations

References used for the calculation method and definitions. Links open in a new tab when available.

[1]
Body Mass Index (BMI) – CDC

CDC overview of BMI categories, calculation methods, and interpretation for adults and children.

[2]
Body Mass Index (BMI) – WHO

WHO global BMI classification thresholds and population-level health risk associations.

Fitness Reference Note

Informational Use: These calculations (BMI, Calories, etc.) are based on standard statistical formulas and are intended for general reference and goal-setting purposes only.

Consult Experts: This tool does not provide medical advice, diagnosis, or treatment. Results may not be accurate for athletes, pregnant individuals, or those with underlying health conditions.

Health Safety: Always consult with a healthcare professional or qualified trainer before beginning any new diet or intensive exercise program.

Privacy First: All calculations are performed locally in your browser. No health data is stored or transmitted to any server.

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