Health calculator
Calculate Body Mass Index in metric or imperial units, see your adult category against the WHO/CDC table, your estimated healthy-weight range, and how far you are from it — with clear limitations, not a diagnosis.
Screening estimate only — not medical advice or a diagnosis.
Your details
Adult BMI categories only apply from age 18. Under 18 shows the BMI number without an adult category — see the child/teen note below.
Your result
BMI
24.2
Healthy weight
A BMI in this range falls within the healthy weight band commonly used for screening adults. This does not confirm overall health — body composition, fitness, and medical history all matter too.
Estimated healthy-weight range
53.5 kg – 72 kg
Estimate based only on BMI 18.5–24.9 for your height — not a target or prescription.
Position
Within healthy range
Your current weight falls inside the healthy BMI range for your height.
Where you fall on the BMI range
Category labels are shown as text (not colour alone) so the chart works for colour-blind readers and in print. Bar domain is capped at BMI 15–45 for readability — an arrow indicates values outside that range.
These are the standard adult BMI classification bands used by the World Health Organization and the US CDC. They apply to adults aged 18 and over and are not used for children or teens (see Adults vs children below).
| Category | BMI range |
|---|---|
| Underweight | 0 – 18.4 |
| Healthy weight | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obesity (Class 1) | 30 – 34.9 |
| Obesity (Class 2) | 35 – 39.9 |
| Obesity (Class 3) | 40 and above |
Metric formula
BMI = kg ÷ m²Weight in kilograms divided by height in metres, squared.
Imperial formula
BMI = 703 × lb ÷ in²Weight in pounds divided by height in inches squared, times 703.
Both formulas describe the same physical ratio and give the same result for the same body — the constant 703 exists only to convert pounds and inches into the metric-equivalent ratio without the person needing to convert units by hand. This calculator normalizes any unit you enter (centimetres, metres, feet & inches, kilograms, pounds, or stone & pounds) to kilograms and metres internally, applies the metric formula once, and displays the result to one decimal place while keeping full precision internally for the healthy-weight range and scenario tools.
Take a height of 170 cm (1.70 m) and a weight of 68 kg. BMI = weight ÷ height² = 68 ÷ (1.70 × 1.70) = 68 ÷ 2.89 = 23.5 (rounded to one decimal place). A BMI of 23.5 falls in the 18.5–24.9 band, so this example is classified as healthy weight.
Take a height of 5 ft 9 in (69 inches total) and a weight of 160 lb. BMI = 703 × weight ÷ height² = 703 × 160 ÷ (69 × 69) = 112,480 ÷ 4,761 = 23.6 (rounded to one decimal place). This example also falls in the healthy weight band.
The calculator above shows an estimated healthy-weight range for the height you entered — this is simply the 18.5–24.9 healthy BMI band converted back into a weight for that specific height (minimum weight = 18.5 × height in metres²; maximum ≈ 24.9 × height in metres²). It is a mathematical conversion of the BMI band, not an individually tailored target, and it carries the same limitations as BMI itself — it says nothing about your muscle mass, frame size, or overall health.
BMI is useful because it is quick, free, and reasonably predictive of health risk across large populations. But because it is calculated from height and weight alone, BMI does not directly measure:
Two people can share the exact same BMI and have very different body compositions and health profiles. Treat a BMI result as a starting point for a conversation, not a conclusion.
The adult BMI bands on this page (underweight, healthy weight, overweight, obesity Class 1–3) only apply from age 18. Children and teenagers are still growing, so a healthy BMI at age 9 is a different number from a healthy BMI at age 16 — the same raw BMI value can mean something completely different depending on age and sex. Proper child and teen BMI assessment compares a child’s BMI against age- and sex-specific percentiles from a reference population (a growth chart), which requires a validated dataset this calculator does not implement. If you enter an age under 18, this calculator shows the raw BMI number only, does not apply an adult category to it, and links directly to the CDC Child and Teen BMI Calculator, which correctly implements that percentile methodology.
Muscle tissue is denser than fat tissue, so at the same height and weight, a muscular person weighs more per unit of volume than someone with a higher proportion of body fat. BMI cannot distinguish between the two — a competitive athlete can register as “overweight” or “obese” by BMI alone while carrying a low, healthy body-fat percentage. For anyone with an athletic build, a body-composition measurement gives a far more meaningful picture than BMI alone.
Weight gain during pregnancy is expected and healthy, and standard adult BMI categories are not designed to interpret it. Clinicians sometimes use pre-pregnancy BMI as one input alongside other factors for gestational weight-gain guidance, but ongoing weight during pregnancy is best discussed directly with a midwife or doctor rather than read from a general calculator.
Body composition changes with age, so the same BMI can reflect a different balance of muscle and fat later in life. BMI can also be less representative for people with certain medical conditions, and for people with a limb difference or amputation, since the standard formula assumes a typical body-weight distribution that a missing limb changes. None of these situations change the BMI formula itself — they change how much weight to put on the result.
Formula: the metric (kg/m²) and imperial (703×lb/in²) BMI formulas are both standard and produce equivalent results for the same body — verified by this page’s own automated tests.
Classification: the adult BMI category boundaries (underweight, healthy weight, overweight, obesity Class 1–3) match the WHO and US CDC adult BMI tables cited below.
Limitations: the “what BMI can and cannot tell you” and special-population notes above summarize widely published, non-controversial limitations of BMI as a screening tool, not this site’s own interpretation.
Body Mass Index (BMI) is a simple screening measure calculated from height and weight. It is used by public-health bodies worldwide as a quick, low-cost way to flag whether someone’s weight may fall outside a typical range for their height — it is not a diagnosis or a body-fat measurement.
Metric: BMI = weight in kilograms ÷ (height in metres)². Imperial: BMI = 703 × weight in pounds ÷ (height in inches)². Both formulas describe the same ratio and give the same result for the same person — this calculator normalizes any unit you enter to metric internally, then applies the formula once.
For adults, the WHO and US CDC both classify 18.5–24.9 as the healthy-weight range, below 18.5 as underweight, 25–29.9 as overweight, and 30 and above as obesity (split into Class 1, 2, and 3). These bands are population-level screening cutoffs, not individual thresholds.
BMI is a reasonably good population-level indicator, but it is a ratio of weight to height only — it cannot see how much of that weight is muscle, fat, bone, or fluid, so it can misclassify individuals even when it works well on average across large groups. Treat it as a starting point, not a verdict.
Not reliably. Muscle is denser than fat, so a muscular, athletic person can have a BMI in the "overweight" or "obese" band while carrying low body fat. BMI cannot distinguish the two — a body-composition measurement (such as skinfold, bioelectrical impedance, or DEXA) gives a clearer picture for very muscular people.
No — not for the category label. A child or teen’s healthy BMI changes as they grow, so their BMI is compared with age- and sex-specific percentiles from a reference population, not the fixed adult bands. This calculator shows the raw BMI number for under-18s but does not apply an adult category to it, and links to the CDC’s own child/teen BMI calculator instead.
No. BMI only uses height and weight — it does not measure body fat percentage, muscle mass, bone density, or where fat is stored on the body, all of which affect health risk independently of the BMI number itself.
Because BMI cannot see body composition or fat distribution. Two people at the same height and weight can have very different amounts of muscle versus fat, different waist-to-hip ratios, and different metabolic health, all of which BMI treats identically.
The formula and the adult classification bands (underweight, healthy, overweight, obesity) are the same for men and women in the WHO/CDC standard used here. Men and women do tend to carry fat differently on average, which is one reason BMI is a screening tool rather than a precise individual health measure.
This calculator does not set a target for you. The 18.5–24.9 band is the commonly cited healthy range for adults, and the healthy-weight range shown above is that band converted to a weight for your height — but the right goal for any individual depends on much more than BMI, and is a conversation for a qualified healthcare professional, not a formula.
Standard adult BMI categories are not designed for pregnancy, when weight gain is expected and healthy. Pre-pregnancy BMI is sometimes used by clinicians as one input for gestational weight-gain guidance, but ongoing pregnancy weight should be discussed with a midwife or doctor rather than read from a general calculator.
It shouldn’t, and on this calculator it won’t — switching between metric and imperial only changes how your height and weight are displayed and edited; the underlying value is converted, not reset or recalculated from scratch, so your BMI stays the same to within normal rounding.
Health & medical disclaimer
This calculator is for general educational use only and is not medical advice. BMI is a population-level screening measure, not a diagnosis — it does not directly measure body fat, muscle mass, bone density, fat distribution, metabolic health, fitness, or individual disease risk, and can be less representative for athletes, older adults, pregnant people, children and teens, and people with certain medical conditions or limb differences. This page does not tell you to gain or lose a specific amount of weight. Consider discussing your result with a qualified healthcare professional, especially alongside any other symptoms or health concerns.