Answer: Enter height and weight and the BMI calculator returns your body mass index value and its WHO band (underweight, normal, overweight, or obese) in both metric and imperial units.
A BMI calculator computes your body mass index — weight in kilograms divided by height in metres squared — and places it in the WHO underweight, normal, overweight, or obese ranges.
Calculate your Body Mass Index
This BMI calculator computes your Body Mass Index instantly from height and weight, in metric or imperial units, and shows which weight category the value falls in along with your healthy weight range for your height.
Body Mass Index is a screening measure developed in the 19th century by Adolphe Quetelet and adopted by the World Health Organization as a population-level yardstick. It applies to adults aged 20 and over; children and teens use percentile-based BMI-for-age charts instead. It does not measure body fat directly, but at a population level it correlates well with fatness and health risk, which is why every clinical check-in starts with it.
BMI = weight in kilograms ÷ (height in meters)². In imperial units it is 703 × pounds ÷ inches². The categories are fixed WHO cutoffs: below 18.5 is underweight, 18.5–24.9 is the normal range, 25–29.9 is overweight, and 30 and above is obese.
For a 1.75 m (about 5 ft 9 in) adult, the healthy weight range works out to 18.5 × 3.0625 = 56.7 kg up to 24.9 × 3.0625 = 76.3 kg (about 125–168 lb). The table below shows how one height maps across the categories.
The category boundaries are the same for adult men and women of every ethnicity in standard use, though some populations use slightly adjusted cutoffs — several Asian health authorities flag increased risk starting at a BMI of 23. The example weights in the table are for a 1.75 m adult, computed directly from the category formulas.
| BMI range | Category | Weight at 1.75 m (5 ft 9 in) |
|---|---|---|
| Below 18.5 | Underweight | below 56.7 kg (125 lb) |
| 18.5–24.9 | Normal weight | 56.7–76.3 kg (125–168 lb) |
| 25–29.9 | Overweight | 76.6–91.5 kg (169–202 lb) |
| 30 and above | Obese | 91.9 kg (203 lb) and up |
BMI's blind spots are well documented: it cannot tell muscle from fat, so very muscular athletes often classify as overweight, and it says nothing about fat distribution — waist circumference adds that dimension and is an easy companion measurement. Older adults carry proportionally more fat at the same BMI, and the metric loses accuracy at extreme heights.
Use BMI as one data point, not a verdict. A single reading paired with waist size, blood pressure, and activity level tells you far more than BMI alone, and trends over time matter more than any one number. If your BMI lands well outside the normal range, that is a prompt for a conversation with a clinician rather than a diagnosis.
BMI's biggest strength is its simplicity: height and weight are measured in every clinic visit with cheap equipment, no body-composition scan required. That is exactly why it has survived since the 19th century as the first-line screen. Its thresholds were set from population statistics to predict health risk at scale, and for that job — flagging who should be looked at more closely — it performs reasonably well.
The metric's known weaknesses are worth respecting. At the same BMI, athletes with high lean mass read too heavy, and adults who have lost muscle with age can read normal while carrying an unhealthy share of fat — so-called normal-weight obesity. Fat location also matters: visceral fat around the organs carries more metabolic risk than subcutaneous fat, which is why waist circumference below roughly 40 inches (102 cm) for men and 35 inches (88 cm) for women is a widely used companion threshold.
For children and teenagers aged 2 to 19, raw BMI cutoffs do not apply — body composition changes through growth, so pediatric practice uses BMI-for-age percentiles from the CDC growth charts. A child above the 85th percentile for their age and sex is classified as overweight, and above the 95th as obese. This calculator's categories apply to adults aged 20 and over only.
Pregnancy, illness, and high-performance training all change what the number means. During pregnancy, weight gain is expected and BMI-based charts are replaced by gestational weight-gain guidance. If you are tracking a fitness transformation, the scale, a tape measure, and progress photos will usually tell you more than a BMI that barely moves while your body composition shifts considerably.
How is BMI calculated?
BMI = weight in kg ÷ height in meters squared. In imperial units, multiply 703 × pounds ÷ inches squared. A 70 kg person at 1.75 m has a BMI of 22.9.
What is a healthy BMI?
For adults aged 20 and over, the WHO normal range is 18.5 to 24.9. Below 18.5 is underweight, 25–29.9 overweight, and 30+ obese.
Is BMI accurate for athletes?
Not reliably. BMI cannot distinguish muscle from fat, so muscular people often score as overweight despite low body fat. Pair BMI with waist circumference or body-composition measurements if you train seriously.
What is my healthy weight range?
It is the weight span that gives a BMI of 18.5–24.9 at your height. For 1.75 m that is about 56.7–76.3 kg (125–168 lb); the calculator shows your exact range.
Does BMI differ for men and women?
The adult categories are the same for both sexes, though women naturally carry more fat at the same BMI. Some health authorities in Asia use lower cutoffs, flagging risk from a BMI of 23.