BMI Calculator
Calculate your body mass index from height and weight — in metric (cm/kg) or imperial — with the WHO category band.
Healthy weight
24.5 BMI
BMI 18.5 – 24.9
A BMI in this range is associated with the lowest population-level health risk for most adults — but it is a single rough indicator, not a diagnosis.
Results update as you type. BMI is a population-level screening tool, not a diagnosis. Athletes, pregnant people, the very tall or very short, and people with very high muscle mass should treat the result with caution.
Formula
BMI is one division:
BMI = weight_kg / (height_m × height_m).
The imperial form folds in the lb→kg and inches→metres conversions:
BMI = (weight_lb × 703) / (height_in × height_in).
Both give the same number for the same person — only the input units change.
When this calculator is useful
BMI is the screening figure national health services across the EU reach for first, so it is worth knowing before a check-up or a new fitness routine. Use this calculator if you want a baseline, you are tracking weight over time, or a health leaflet or app has quoted a number you want to make sense of. It works in metric — height in metres or centimetres and weight in kilograms, the standard across most of the euro area — and will also accept imperial units if that suits you better.
It is intended for adults aged 18 and over. For most people it gives a reasonable first read on whether weight sits in a range linked to lower long-term health risk — but it is a screening signal, not a diagnosis. If the result is unexpected, treat it as a prompt to look at your waist measurement, activity and diet, and to discuss it with a doctor rather than to act on the figure on its own.
Understanding your result
The WHO bands used across EU member states sort your number into one of four groups. Under 18.5 is underweight, which can indicate under-nutrition or an underlying condition. From 18.5 to 24.9 is the healthy-weight range, associated in population research with the lowest all-cause mortality. From 25 to 29.9 is overweight, and 30 or above is obesity, divided into Class I, II and III as risk increases.
Read the band as an indicator, not a conclusion. A reading of 26 does not mean you are ill, and 23 is no promise of good health — it depends on muscle mass, where you carry fat, your blood pressure and your blood-sugar results. Because the bands reflect risk across whole populations, use yours to judge whether a closer look is worthwhile, and note that clinical pathways differ from one country to the next.
A worked example
Take an adult who is 175 cm tall and weighs 75 kg. The calculation is 75 divided by 1.75 squared, which is 75 divided by 3.0625, giving a BMI of about 24.5 — just inside the healthy-weight range. If the same person reached 80 kg, their BMI would rise to about 26.1, moving them into the overweight band on a gain of five kilograms. Small changes in weight shift the number more than people expect, so a steady trend over months tells you far more than any single reading.
Points to be careful about
BMI is straightforward to work out but easy to over-interpret. Keep these limits in mind before you read much into your score.
- Treating it as a body-fat measure — BMI cannot separate muscle from fat, so people with high muscle mass often score in the overweight band despite carrying little fat.
- Ignoring fat distribution — a waist over 102 cm for men or 88 cm for women signals raised risk even when BMI looks fine, and several EU countries flag risk from 94 cm and 80 cm.
- Using adult bands for under-18s — children and teenagers are assessed on age-and-sex percentiles, not these thresholds.
- Overlooking ethnicity — for South Asian, East Asian and several other groups, WHO suggests lower action thresholds of about 23 and 27.5.
European health guidance and thresholds
Across the EU, national health services use the WHO bands as a common screening reference, but clinical pathways, follow-up tests and exact thresholds vary from one country to the next. The WHO recommends lower action points — around 23 for overweight and 27.5 for obesity — for South Asian, East Asian and several other populations, because cardiometabolic risk rises at a lower BMI, and many EU countries have adopted these in practice. The harmonised IDF metabolic-syndrome waist thresholds are also more conservative for European populations than older cut-offs, which is why waist measurement is a valuable companion to BMI.
Whatever your number, the sensible next steps are consistent — check your waist, look honestly at activity and diet, and discuss the result with your doctor, who can interpret it alongside your blood pressure and blood-sugar readings. Because guidance is set nationally rather than EU-wide, ask your GP or a local specialist for the protocol that applies where you live if your result or your background suggests a closer look is warranted.
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Frequently asked questions
How do you calculate BMI?▾
BMI is weight in kilograms divided by height in metres squared (kg/m²). 75 kg at 1.75 m → 75 ÷ 3.0625 = 24.49. The formula was published by Adolphe Quetelet in 1832; the World Health Organization adopted it in the 1990s as a standard screening figure.
What are the WHO BMI categories?▾
Under 18.5 = underweight; 18.5–24.9 = healthy weight; 25–29.9 = overweight; 30 and above = obesity, split into Class I (30–34.9), Class II (35–39.9), and Class III (≥40). These bands are used across EU member states' national health services, though specific clinical pathways and screening thresholds vary by country and by ethnicity.
Does BMI work for everyone?▾
No. BMI is a population screening tool and is unreliable at the individual level for: athletes and people with high muscle mass (lean weight inflates BMI), pregnant or lactating people (extra weight is normal), the elderly (lean mass decreases with age, so BMI underestimates fat), the very tall or short (the squared denominator distorts at extremes), and children and teens (use age-sex percentiles instead). Treat the result as a starting point, not a verdict.
What about waist circumference?▾
Waist measurement captures fat distribution in a way BMI cannot. WHO thresholds: men with a waist over 102 cm or women over 88 cm have substantially higher cardiometabolic risk regardless of BMI. Some EU countries use lower thresholds (94 cm men / 80 cm women) as the first level of risk; the harmonised IDF metabolic syndrome thresholds are even more conservative for European populations.
Why is BMI used at all if it has so many limits?▾
Because it's almost free to calculate (just height and weight), easy to compare across populations, and reasonably correlated with body fat percentage on average. National health services use it as a screening signal — a high BMI prompts further tests; nobody is diagnosed on BMI alone. More accurate measures (DEXA, hydrostatic weighing, bioelectrical impedance) are slower and costlier.
Are there ethnicity-adjusted BMI bands?▾
Yes — for South Asian, East Asian, and several other ethnic groups, cardiometabolic risk rises at lower BMIs. WHO guidance suggests action thresholds of 23 (overweight) and 27.5 (obese) for these populations, several units below the standard cut-offs. Adopted in clinical practice across many EU countries; ask your GP or specialist for the local protocol if relevant to you.