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.
Your details
cm
kg
yrs
Adult BMI categories only apply from age 18. Under 18 shows the BMI number without an adult category — see the child/teen note below.
Shown for reference only — it does not change your BMI. Waist size can add useful context alongside BMI for some people.
Estimate only — not medical advice. Consult a qualified healthcare professional before acting on this result.
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.
Distance from the healthy BMI range
Within the range
Your weight is inside the healthy BMI range for your height.
BMI is a screening measure, not a diagnosis. It does not tell muscle from fat, and the cut-offs used vary between populations. Adult categories do not apply under 18 or during pregnancy.
Bands are labelled in text, and Class 1–3 are the three obesity classes. The bar covers BMI 15–45 for readability; an arrow marks values outside that range.
Your result
Explore scenarios (optional)
See what BMI a different weight would give — not a recommendation to gain or lose weight.
kg
BMI would be 24.2 at this weight, same height.
≈ 63.6 kg at your entered height would give a BMI of 22.0.
kg
Gaining 5kg → BMI 26.0. Losing 5kg → BMI 22.5.
What this tool covers
With clear limitations, not a diagnosis.
Adult BMI category (WHO/CDC bands)
Estimated healthy-weight range
Distance from that range
Separate under-18 handling
Metric & imperial Healthy-weight range Not a diagnosis
Screening estimate only — not medical advice or a diagnosis.
Updated 15 September 2026
One ratio, two formulas, and the 703 that keeps them equal
Metric formula
BMI = kg ÷ m²
Weight in kilograms divided by height in metres, squared.
Imperial formula
BMI = 703 × lb ÷ in²
Weight 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.
Doing the metric side by hand is short arithmetic. 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.
The imperial route reaches the same place by a different arithmetic. 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.
That equivalence is what makes the unit toggle above safe to use mid-entry. 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.
Where the lines fall at 18.5, 25 and 30 — and the lines this tool leaves alone
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 why an age under 18 gets no category below).
Adult BMI classification bands and ranges
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
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.
The NHS in the UK uses the same WHO adult BMI classification bands (18.5–24.9 healthy, 25–29.9 overweight, 30+ obesity) shown on this page, so the category you see here matches NHS guidance for adults.
Nothing in the table splits by sex, and that is deliberate. 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.
One published set of cutoffs this calculator deliberately does not apply: the WHO also publishes alternative, lower BMI action points for Asian populations (overweight from 23, obesity from 27.5, rather than 25 and 30), reflecting research that health risk can rise at a lower BMI in some Asian populations. This calculator applies the standard WHO/CDC adult bands used worldwide, not the Asian-specific cutoffs — if your healthcare provider uses the Asian action points, compare your BMI number against those thresholds directly.
Reading the 18.5–24.9 band backwards into a weight for your height
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.
Which is why the figure is shown as a range and never as a goal. 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.
The distance figure beside it is the same conversion read as a gap: how far the weight you entered sits from the nearest edge of that converted band, in the units you are already using. It is a subtraction, nothing more — not a recommendation to change your weight by this amount — and it inherits every limitation above.
Two bodies can hand this calculator the same number and share nothing else
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.
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:
Body fat percentage
Muscle mass
Bone density
Where fat is stored on the body (fat distribution)
Metabolic health or fitness
Pregnancy-related weight changes
Individual disease risk
Those are absences in the input, not gaps in the arithmetic. 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.
Two people can share the exact same BMI and have very different body compositions and health profiles. 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. Treat a BMI result as a starting point for a conversation, not a conclusion.
None of that makes the measure useless, and it is worth being precise about where it does work. 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.
Why an age under 18 gets a number here and no category
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.
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. If you enter an age under 18, this calculator therefore 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.
Athletes, pregnancy and older age: the same formula, less weight on the answer
The advanced options in the calculator carry four checkboxes for exactly these situations — athletic build or high muscle mass, pregnant or breastfeeding, age 65 or older, and limb difference or amputation. Ticking one shows relevant notes, and pregnant or breastfeeding shows the BMI number without a category; none of them changes the calculation. Neither does the optional waist circumference field beside them, which is shown for reference only and does not change your BMI. What these situations change is how much the number is worth reading, which is what the notes below set out.
Athletes and high muscle mass
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 (such as skinfold, bioelectrical impedance, or DEXA) gives a far more meaningful picture than BMI alone.
Pregnancy
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. That is why ticking pregnant or breastfeeding shows the number with a notice instead of a category.
Older adults and other considerations
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.
Sources and methodology
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 notes above on what BMI cannot separate, and on athletes, pregnancy, older adults and under-18s, summarize widely published, non-controversial limitations of BMI as a screening tool, not this site’s own interpretation.
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This page is the work of Jay Sudha, who is not a doctor, dietitian, or other licensed clinician, and no licensed medical professional has vetted it yet. Treat it as general education, not medical advice — for anything that matters for your health, talk to a qualified professional. 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.
Published the BMI calculator with metric and imperial formulas, adult WHO/CDC category bands, and a healthy-weight range.
Launched Calculator Matters' Health category with this calculator as its first tool.
Pregnancy or breastfeeding now shows the BMI with a notice in place of a category; every category shares one neutral color; the result explains what BMI screens for and adds the National Alliance for Eating Disorders helpline; each source now states what it backs.
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