BMI Calculator
Calculate your Body Mass Index and see where you fall on the WHO weight categories.
BMI Calculator — your inputs
- Height
- 175 cm
- Weight
- 70 kg
- Unit system
- Metric
Key takeaways
- BMI is weight divided by height squared — a screening number, not a measurement of body fat and not a diagnosis.1
- For adults, the WHO calls 18.5 to 24.9 kg/m² the normal range. The boundaries are population thresholds, not a line between healthy and unhealthy on the day you cross them.2
- BMI cannot tell muscle from fat. A lifter and a sedentary person of the same height and weight get the same number and are in very different health.6
- It does not apply as written to children, pregnant people, or many older adults — each needs a different reference.3
- Read it alongside something that reflects where the weight sits, such as waist-to-hip ratio or body fat percentage.
How to use this calculator
Choose your preferred unit system at the top of the calculator.
Enter your height and weight.
Your BMI, category, and healthy weight range update automatically (or tap Calculate).
Understanding your result
BMI is a screening number that relates weight to height. It does not measure body fat directly, but it tracks closely at a population level.
Your result falls into one of the WHO adult categories set out in the BMI table for adults below, and the range gauge shows exactly where you sit on that spectrum.
What BMI actually measures
Body Mass Index is a ratio, and only a ratio: your mass divided by the square of your height. Adolphe Quetelet devised it in the 1830s as a way of describing populations, not individuals, and it was never intended as a clinical measure of a single person's health. It became one because it is cheap, it needs no equipment beyond a scale and a tape, and across large groups it tracks body fatness closely enough to be useful.1
That history explains both why BMI is everywhere and why it frustrates people. It is a good instrument for the job it was built for — comparing groups, tracking a population over time, deciding who might benefit from a closer look — and a blunt one for the job people usually want from it, which is a verdict on themselves.
The one-sentence version
A BMI outside the normal range is a reason to look more closely, not a conclusion. It tells you something about your weight relative to your height, and nothing at all about what that weight is made of.
BMI table for adults
These are the World Health Organization's adult classifications, used for both men and women aged 20 and over.1 They are the categories this calculator reports.
| Classification | BMI (kg/m²) | BMI Prime |
|---|---|---|
| Severe thinness (danger) | Below 16 | Below 0.64 |
| Moderate thinness (warning) | 16 – 17 | 0.64 – 0.68 |
| Mild thinness (warning) | 17 – 18.5 | 0.68 – 0.74 |
| Normal (success) | 18.5 – 25 | 0.74 – 1 |
| Overweight (warning) | 25 – 30 | 1 – 1.2 |
| Obese class I (danger) | 30 – 35 | 1.2 – 1.4 |
| Obese class II (danger) | 35 – 40 | 1.4 – 1.6 |
| Obese class III (danger) | 40 and above | 1.6 and above |
- Severe thinness (12–16)
- Moderate (16–17)
- Mild (17–18.5)
- Normal (18.5–25)
- Overweight (25–30)
- Obese I (30–35)
- Obese II (35–40)
- Obese III (40–45)
| Category | Range |
|---|---|
| Severe thinness | 12 to 16 kg/m² |
| Moderate | 16 to 17 kg/m² |
| Mild | 17 to 18.5 kg/m² |
| Normal | 18.5 to 25 kg/m² |
| Overweight | 25 to 30 kg/m² |
| Obese I | 30 to 35 kg/m² |
| Obese II | 35 to 40 kg/m² |
| Obese III | 40 to 45 kg/m² |
The thing worth noticing on that scale is how much room the normal band covers. At 175 cm it spans roughly 56.7 kg to 76.3 kg — a 20 kg window. People often read BMI as though it names a single correct weight; it names a range wide enough to hold very different-looking bodies.
Why the same BMI can mean different things
BMI is a measure of excess weight, not excess fat, and the gap between those two is where almost every complaint about it lives. A study of more than 13,000 adults found BMI-defined obesity missed roughly half the people who were obese by direct body-fat measurement — good specificity, poor sensitivity.6 The number is much better at confirming that someone carries excess fat than at ruling it out.
- Muscle. Muscle is denser than fat. A trained athlete can sit in the overweight or obese band with single-digit body fat. This is the most cited limitation and the most real one.
- Age. Older adults tend to carry more fat and less muscle at the same BMI, so a 'normal' reading can hide meaningful loss of lean mass.
- Sex. At an equivalent BMI, women generally carry more body fat than men — which is why body-fat references are sex-specific and BMI is not.
- Ancestry. Cardiometabolic risk rises at lower BMI values in many Asian populations; WHO discussed additional public-health action points at 23 and 27.5 kg/m² rather than redrawing the categories.4
- Fat distribution. Two people at BMI 27 carrying the same fat mass around the waist versus the hips face measurably different risk. BMI cannot see the difference; a tape measure can.
This is now the official position too
In 2023 the American Medical Association adopted a policy stating that BMI is an imperfect measure that should be used only alongside other valid measures — such as visceral fat, body composition, and waist circumference — rather than on its own.7
None of this makes BMI useless. The largest analysis of the question, pooling 239 studies and roughly ten million people, found mortality lowest between about 20 and 25 kg/m² and rising steadily above it.5 That relationship is real. It is a statement about populations, and about the direction of risk — not a prediction about the person reading this page.
BMI for children and teens
Children are not small adults. Body composition changes continuously through growth and puberty, so a fixed threshold like 25 kg/m² is meaningless at age nine. The CDC instead compares a child's BMI to others of the same age and sex, producing a percentile.3
| Category | Percentile range |
|---|---|
| Underweight (warning) | Below the 5th |
| Healthy weight (success) | 5th – 85th |
| Overweight (warning) | 85th – 95th |
| Obesity (danger) | 95th and above |
This calculator reports adult categories
If you enter an age under 20 it will say so, but the category it shows is still the adult one. For a child or teenager, use the CDC's BMI-for-age tool or ask a pediatrician — a percentile is the only meaningful answer at that age.
BMI Prime and the Ponderal Index
Two derived numbers appear often enough alongside BMI to be worth knowing.
- BMI Prime
- Your BMI divided by 25 — the upper bound of the normal range. It is dimensionless, so it reads as a plain ratio: 0.92 means you are at 92% of the upper limit, and anything above 1.0 is above it. Useful because it compares cleanly across populations that use different upper thresholds.
- Ponderal Index
- Mass divided by height cubed rather than squared. Because human bodies do not scale as perfect squares, BMI drifts high for tall people and low for short ones; the Ponderal Index is more stable at the extremes of height, which is why it is preferred in neonatal medicine and for very tall or very short adults.
- Fat-free mass
- Everything in the body that is not fat: muscle, bone, organs, water. Two people with the same BMI and different fat-free mass are in genuinely different health, and BMI reports them identically.
What to do with the number
A BMI reading is most useful as a prompt, and it becomes far more informative when it is not the only thing you have.
- Add a waist measurement. Where fat sits predicts risk better than how much you weigh. The Waist-to-Hip Ratio Calculator takes thirty seconds with a tape measure.
- Estimate body composition. The Body Fat Calculator uses the U.S. Navy circumference method and answers the question BMI cannot.
- Look at the trend, not the reading. A single BMI is a snapshot. The direction it moves over months is the part that carries information.
- Set a range, not a target. The Healthy Weight Calculator converts the normal BMI band back into kilograms or pounds for your height — usually a wider window than people expect.
- Take a result at the edges to a clinician. Severe thinness and obese class II or III are the readings where a professional assessment genuinely changes what happens next.
If you are pregnant
BMI is not interpretable during pregnancy — weight gain is expected and healthy. Pre-pregnancy BMI is used, to set the recommended gain for the pregnancy; the Pregnancy Weight Gain Calculator does that from Institute of Medicine guidance.
Terms used on this page
- Screening tool
- A cheap, fast test used to decide who needs a closer look. Screening tools are designed to be over-inclusive; being flagged by one is not a diagnosis.
- Percentile
- A rank against a reference group. A child at the 85th percentile has a higher BMI than 85% of children of the same age and sex.
- Visceral fat
- Fat stored around the abdominal organs, as opposed to under the skin. It carries substantially more cardiometabolic risk, and BMI cannot detect it.
The formula
- Height 175 cm = 1.75 m, weight 70 kg
- BMI = 70 / (1.75 × 1.75)
- BMI = 70 / 3.0625
Source: WHO BMI formula. Published clinical/scientific formula.
Limitations
- BMI does not distinguish muscle from fat mass — very muscular people can register as 'overweight' without being unhealthy.
- It is not validated the same way for children, pregnant women, or older adults.
- BMI is a population-level screening tool, not a diagnosis of health.
References
- 1.Obesity: preventing and managing the global epidemic (WHO Technical Report Series 894). World Health Organization, 2000.
- 2.A healthy lifestyle — WHO recommendations (body mass index). World Health Organization, 2010.
- 3.About BMI for Children and Teens. Centers for Disease Control and Prevention, 2024.
- 4.Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. WHO Expert Consultation, The Lancet 363(9403):157–163, 2004.
- 5.Body-mass index and all-cause mortality: individual-participant-data meta-analysis of 239 prospective studies. Global BMI Mortality Collaboration, The Lancet 388(10046):776–786, 2016.
- 6.Accuracy of body mass index in diagnosing obesity in the adult general population. Romero-Corral et al., International Journal of Obesity 32(6):959–966, 2008.
- 7.AMA adopts new policy clarifying role of BMI as a measure in medicine. American Medical Association, 2023.
Frequently asked questions
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Read articleNot medical advice. This calculator is for general informational purposes only and is not a substitute for professional medical guidance. Always consult a qualified healthcare provider before making decisions about your health. Read the full medical disclaimer.
Printed from mystatura.com — for general information only, not medical advice.