BMI Calculator

BMI is a screening ratio of weight to height. This calculator uses kilograms and meters internally — pounds and inches convert first — then shows the adult WHO category bands. Treat the result as a first look, not a verdict on health, fat, or disease.

The formula, a 70 kg / 1.75 m walkthrough, and a slider demo live in How to Calculate BMI. If you care about energy rather than the ratio, the BMR Calculator and Calorie Calculator estimate rest and daily calories. A tape-based Body Fat Calculator is a different kind of estimate.

BMI categories and what they mean

Adult tables from the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC) group BMI into four main bands: underweight below 18.5, normal (CDC says “healthy weight”) from 18.5 through 24.9, overweight from 25 through 29.9, and obese at 30 and above. Those are the same adult cutoffs this page paints on the scale.

Plainly, the bands compare your mass with the square of your height. They do not say why the mass is there — muscle, fat, bone, or water — and they were built for population screening, not for diagnosing a person. CDC also splits obesity into classes (30–34.9, 35–39.9, 40+), which this widget does not use. If your number sits near a boundary, a 0.1 shift can change the label; that is the table talking, not a sudden change in health.

BMI chart by height and weight

The grid below is a compact adult lookup: a few heights against a few weights, colored with the same WHO bands as the scale. It is not every kilogram and centimeter. Pick the closest row and column, then use the calculator for your exact pair. Metric matches the SI formula; US customary inputs convert to the same kg/m².

Height	50 kg	60 kg	70 kg	80 kg	90 kg	100 kg
1.55 m	20.8	25.0	29.1	33.3	37.5	41.6
1.65 m	18.4	22.0	25.7	29.4	33.1	36.7
1.75 m	16.3	19.6	22.9	26.1	29.4	32.7
1.85 m	14.6	17.5	20.5	23.4	26.3	29.2

Underweight (<18.5)
Normal (18.5–24.9)
Overweight (25–29.9)
Obese (≥30)

Adult BMI (kg/m²) for selected heights and weights, colored by WHO bands. A screening chart, not a diagnosis.

Limitations of BMI

BMI is a tidy ratio, and that is both the point and the problem. It only knows two things: how heavy you are and how tall you are. It cannot see muscle mass. A weightlifter and someone with little muscle can share a BMI; one may have a high lean mass, the other a high fat mass, and the number will not tell them apart. That is why athletes often land in overweight or obese on paper while their body fat is low. Bone density is missing too. Heavier bones add kilograms without adding risk in the way extra visceral fat does, so two people with the same BMI can have different skeletons.

Age and sex do not enter the adult formula. The WHO cutoffs are the same for a 22-year-old and a 70-year-old, and the same for men and women, even though fat distribution, muscle, and what counts as a typical weight tend to shift over a lifetime. Older adults can lose muscle and keep a “normal” BMI while carrying more abdominal fat. Ethnicity and where fat sits are outside the arithmetic as well. Pregnancy, edema, and amputations also throw it off. Use BMI the way a clinic does: as a screen. If the number is surprising, look at composition, waist, labs, and history — not a diagnosis. The Body Fat Calculator and Lean Body Mass Calculator are still estimates, just different ones.

Health risks of a high BMI

Population studies link higher adult BMI, especially in the obese range, with a higher chance of cardiovascular disease (heart disease and stroke), type 2 diabetes, and joint problems such as knee osteoarthritis. Extra mass loads joints, and extra adipose tissue — particularly around the abdomen — tracks with blood pressure, lipids, and insulin resistance.

That is a statistical pattern, not a prediction about you. Plenty of people with a high BMI have reassuring blood work; plenty with a “normal” BMI do not. Smoking, fitness, family history, sleep, and medications all move risk. A high BMI is one flag among many, not a sentence. This page does not diagnose disease or prescribe weight loss. If cardiovascular disease, diabetes, or joint pain is already in the picture, or the number keeps climbing, that is a reason to talk with a clinician who can look at the whole file — not a reason to panic over a screening ratio.

BMI for children

For children and teens, the adult 18.5 / 25 / 30 cutoffs do not apply. Growing bodies need age- and sex-specific comparison. CDC BMI-for-age growth charts (roughly ages 2–19) plot the same kg/m² formula as a percentile among peers: underweight below the 5th percentile, healthy weight from the 5th to under the 85th, overweight from the 85th to under the 95th, and obesity at or above the 95th. This calculator reports the adult number and adult bands only. It does not compute percentiles. For a child, take the BMI to a pediatric clinician who can plot it on a CDC growth chart and watch the trend, not a single snapshot.

BMI vs waist circumference

BMI does not know where mass sits. Fat around the waist (visceral fat) is more strongly tied to metabolic risk than fat on the hips or thighs. A waist tape is a crude complement: it still is not a scan, but it catches the “normal BMI, large middle” pattern that the ratio misses. Thresholds vary by sex and by guideline — CDC materials often mention about 40 inches (102 cm) for men and 35 inches (88 cm) for women as a higher-risk zone; WHO uses stepped cutoffs that also differ by population. Measure standing, after a normal breath out, between the last rib and the hip bone. Use it with BMI, not instead of a clinician.

When to talk with a clinician

Talk with a clinician if the number worries you, if weight has changed fast without trying, if you have symptoms you cannot explain (unusual fatigue, breathlessness, joint pain), or if you already live with heart disease, diabetes, or an eating-disorder history. Also ask before chasing a BMI target during pregnancy, after bariatric surgery, or while you are still growing. Bring the number; they will put it next to waist, history, and labs. This tool will not.

Worked example: 70 kg at 1.75 m

Metric: weight 70 kg and height 1.75 m → BMI = 70 / (1.75²) = 70 / 3.0625 ≈ 22.9 kg/m² (typical "normal" adult range).

\[ \mathrm{BMI}=70/(1.75)^{2}\approx 22.9 \]

Frequently asked questions

What BMI range is healthy?

For most adults, WHO and the CDC treat 18.5 to 24.9 as the usual healthy-weight band (WHO still says “normal”). Below 18.5 is underweight; 25 to 29.9 is overweight; 30 and above is obese. Those cutoffs are a population screen, not a personal target written on your body. A muscular adult can sit above 25 and still be metabolically fine; an older adult in the “normal” band can still carry a lot of abdominal fat. Use the range as a starting map, then look at waist, fitness, blood work, and how you feel — and talk with a clinician before treating the number as a goal.

Is BMI a diagnosis of health?

No. BMI is a screening ratio of mass to height squared. It does not measure body fat, muscle, or medical risk on its own—athletes and older adults are common edge cases.

Why doesn't BMI work for athletes?

BMI treats every extra kilogram as extra mass, whether it is muscle, fat, or water. Athletes who train for strength or power often have more muscle and denser bone than the tables assume, so the ratio climbs into overweight or obese even when body fat is low. The formula also cannot see fitness or fat location. That is a known limitation, not a glitch in this calculator. If you train seriously, read BMI as a coarse screen and pair it with waist, performance, or a composition estimate such as the Body Fat Calculator — and let a clinician interpret the mix rather than chasing a “normal” band built for populations, not for sport.

How do US customary inputs convert?

The tool converts pounds to kilograms and inches to meters before applying BMI = w/h², so Metric and US unit systems stay comparable.

Does this calculator work for children?

It will compute the same kg/m² number, but the adult WHO bands on this page do not apply to children or teens. CDC growth charts interpret BMI as an age- and sex-specific percentile. Take a child's result to a pediatric clinician rather than reading the adult labels.

Should I use waist size with BMI?

A waist measurement can catch abdominal fat that BMI misses, especially the “normal BMI, large middle” pattern. Thresholds vary; CDC often cites about 40 inches for men and 35 inches for women as a higher-risk zone. It is still a screen, not a diagnosis.

References

Assumptions and limitations

These fitness results are not a medical diagnosis or treatment plan. They use the named screening formulas only and cannot replace advice from a qualified clinician.

This widget uses adult WHO cutoffs on the scale. It does not compute child BMI-for-age percentiles, waist risk, or body-fat percentage.