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The Calculator Corner

BMI Calculator

Calculate your Body Mass Index for adults 20+, with a healthy weight range and optional Asian BMI cutoffs.

Style

BMI

24.2

Normal weight
Healthy weight range for this height
53.5 kg – 72 kg

What BMI measures, and what it does not

Body Mass Index is weight divided by height squared. That is the entire definition. It was devised in the 1830s as a way of describing populations, and it does that job well: across large groups, average BMI tracks meaningfully with health outcomes.

What it cannot do is distinguish between kinds of mass. Muscle, fat, bone and water all enter the formula identically, and nothing in it knows where on the body that mass sits — which matters, because abdominal fat carries more metabolic risk than the same weight elsewhere. BMI is a screening number, not a diagnosis, and it is most useful as one input among several rather than as a verdict on its own.

Using this BMI calculator

Enter your height and weight and the BMI appears with its category, along with the BMI values at each boundary — where you would cross into normal, overweight and obese — and the weights those boundaries correspond to at your height. The gauge marks the same boundaries visually.

Two settings sit in the customize panel. Units switches between metric (cm, kg) and US (ft/in, lb). BMI classification switches between the standard WHO/CDC cutoffs and the WHO's Asian public-health-action cutoffs — see below for why that choice exists.

This calculator is for adults aged 20 and over. Children and teenagers are assessed against age- and sex-specific percentile charts instead, and running their numbers through an adult formula produces a figure that means nothing.

The formula, worked through

In metric, BMI = weight in kilograms ÷ (height in metres)². Someone 170 cm and 70 kg computes as 70 ÷ 1.70² = 70 ÷ 2.89 = 24.2 — within the normal band, close to its upper edge.

In imperial units the same relationship needs a conversion factor: BMI = (weight in pounds ÷ (height in inches)²) × 703. At 5 ft 7 in (67 in) and 154 lb, that is (154 ÷ 4,489) × 703 = 24.1 — the same person, the same answer, give or take rounding.

Because height is squared, BMI is far more sensitive to height than to weight. A centimetre of measurement error moves the result more than most people expect, which is another reason to read a BMI near a boundary as “near a boundary” rather than as a category.

The categories, and the Asian cutoffs

Under the WHO/CDC standard for adults: below 18.5 is underweight, 18.5–24.9 is normal weight, 25–29.9 is overweight, and 30 or above is obese.

The Asian cutoffs option exists because those thresholds were derived largely from European populations. Research consistently finds that people of South and East Asian descent face comparable metabolic risk at lower BMI values, so the WHO publishes lower public-health-action points: normal weight 18.5–22.9, overweight 23–27.4, obese from 27.5. Switching the setting does not change your BMI — only the band it falls into.

Where BMI misleads most is at the extremes of body composition. A muscular athlete can register as overweight or obese with very little body fat, and an older or sedentary person can sit comfortably in the normal band while carrying a high proportion of it. Waist circumference, waist-to-height ratio and body-fat measurement all capture things BMI cannot. Treat the number here as a starting point for a conversation with a clinician who can see the rest of the picture, not as a substitute for one.

FAQ

How is BMI calculated?
BMI = weight (kg) ÷ height (m)². In US units it's weight (lb) × 703 ÷ height (in)², which is mathematically the same formula converted to imperial units. This calculator does the unit conversion for you — just pick Metric or US units in the customize panel (top-right gear icon).
What do the BMI categories mean?
Under the WHO/CDC standard used for most adults: below 18.5 is Underweight, 18.5–24.9 is Normal weight, 25–29.9 is Overweight, and 30+ is Obese. These bands are for adults aged 20 and over — children and teens are assessed against age- and sex-specific percentile charts instead, which this calculator doesn't cover.
Why does this calculator offer an "Asian cutoffs" option?
Research shows people of South and East Asian descent tend to face higher health risks at lower BMI values than the general WHO cutoffs assume. WHO's public-health-action points for Asian populations lower the thresholds: Normal weight is 18.5–22.9, Overweight is 23–27.4, and Obese starts at 27.5. Open the customize panel (top-right gear icon) and switch "BMI classification" to see your category under either standard.
Is BMI accurate for athletes or very muscular people?
Not always. BMI only relates weight to height — it can't distinguish muscle from fat, so muscular or very athletic people are sometimes classified as "overweight" despite low body fat. It also doesn't account for age, sex, or body-fat distribution. Waist circumference, waist-to-hip ratio, or a body-fat percentage measurement give a fuller picture alongside BMI.
What's a healthy weight range for my height?
The gauge below your BMI marks the BMI value at each color boundary — where you cross into Normal, Overweight, and Obese. The span between the first two of those is your healthy BMI range (18.5–24.9 standard, or 18.5–22.9 under Asian cutoffs); the summary line above the gauge converts your distance from that range into an actual amount of weight to gain or lose.

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