BMI Calculator
Check your body mass index and healthy weight range.
Height
Weight
Body Mass Index
24.2
Category
Normal
Healthy Weight Range
53.5 – 72.0 kg
BMI is a general screening tool and doesn't account for muscle mass, bone density or body composition. It isn't a diagnosis — talk to a healthcare provider for personalized advice.
How this calculator works
Body Mass Index divides your weight in kilograms by the square of your height in metres (BMI = weight ÷ height²). It's the same formula doctors and public health bodies like the WHO use for population-level screening, which is why it's the most widely quoted weight metric — not because it's the most accurate, but because it only needs a scale and a tape measure, no special equipment.
Worked example
Someone who is 170cm tall and weighs 70kg has a BMI of 70 ÷ (1.70 × 1.70) = 24.2 — just inside the "normal weight" band. The same person at 80kg would have a BMI of 27.7, putting them in the "overweight" band despite only a 10kg difference, which shows how sensitive the metric is to small changes in weight at a fixed height.
The four BMI categories
Below 18.5 is classified as underweight, 18.5–24.9 as normal weight, 25–29.9 as overweight, and 30 and above as obese (further split into Class I, II and III by most health bodies). These bands come from population studies linking BMI to health outcomes, not from any individual person's actual body composition.
Where BMI breaks down
BMI can't distinguish muscle from fat, so athletes and anyone who strength-trains seriously often reads as "overweight" or even "obese" despite low body fat. It's also a poor fit for growing children and teenagers (who need age- and sex-specific percentile charts, not adult cutoffs), pregnant women, and older adults, whose healthy body fat percentage tends to run higher than a younger adult's at the same BMI.
BMI cutoffs differ by ethnicity
The standard 25/30 cutoffs were derived mainly from European population data. Because South and East Asian populations tend to develop weight-related health risks at a lower BMI, the WHO and several national health bodies recommend lower action points for Asian adults — commonly 23 for "overweight" and 27.5 for "obese" — even though this calculator, like most general-purpose tools, uses the standard global cutoffs by default.
What to check alongside BMI
Because BMI ignores where fat is actually distributed, waist circumference and waist-to-height ratio are better predictors of cardiometabolic risk at the same BMI. For a fuller picture, try the Body Fat Percentage Calculator for an estimate that accounts for body composition, or the Ideal Body Weight Calculator for a frame-based target instead of a single index.
Where BMI comes from
BMI was devised in the 1830s by Belgian mathematician Adolphe Quetelet as a way to study population averages, not individual health — it was never intended as a personal diagnostic tool, which is worth remembering whenever a single number gets treated as a verdict rather than a starting point for a conversation with a healthcare provider.
Frequently Asked Questions
What is a healthy BMI range?
For most adults, the World Health Organization defines 18.5–24.9 as the normal weight range, under 18.5 as underweight, 25–29.9 as overweight, and 30+ as obese. BMI is a screening tool, not a diagnosis — it doesn't distinguish muscle from fat.
How is BMI calculated?
BMI is weight in kilograms divided by height in metres squared (kg/m²). This calculator handles the conversion automatically whether you enter metric or imperial units.
Is BMI accurate for athletes or older adults?
Not reliably. BMI can't tell muscle from fat, so very muscular people often read as "overweight" despite low body fat, and older adults can have a normal BMI while carrying more fat and less muscle than the number suggests. Body fat percentage is a better measure in these cases.
Are BMI cutoffs the same for everyone?
No. The standard 18.5/25/30 cutoffs come mainly from European population data. Because South and East Asian populations tend to develop weight-related health risks at a lower BMI, the WHO and several national health bodies recommend lower cutoffs for Asian adults — commonly 23 for overweight and 27.5 for obese.
Does BMI work for children and teenagers?
No — children and teens are still growing, so their healthy weight range changes with age and sex. Pediatric guidelines use BMI-for-age percentile charts instead of the fixed adult cutoffs this calculator (and most general BMI tools) use.
Who invented BMI, and was it meant for individual health?
BMI was devised in the 1830s by Belgian mathematician Adolphe Quetelet to study population averages, not individual health — it was never designed as a personal diagnostic tool, which is part of why it's best treated as a rough screening number rather than a verdict.
This tool provides general estimates for informational purposes only and isn't a substitute for professional medical advice. Consult a doctor or qualified healthcare provider before making decisions about your health.