BMI

24.2215

Computed from default inputs using graph `synth-bmi`.

Weight

Range: 20 - 300

BMI divides weight in kilograms by height in meters squared, and everything useful and everything misleading about it follows from that simplicity. The WHO classification applied here — under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30 and above obese — was built for population screening, where it tracks health risk well across large groups. For one person it is a starting point, not a verdict: the ratio cannot tell muscle from fat, which is why this calculator accepts an optional body-fat percentage to flag the athlete case, and why a 2004 WHO expert consultation recommended lower action points (23 and 27.5) for many Asian populations, in whom metabolic risk rises at lower BMI. Enter honest numbers — self-reported height runs tall and weight runs light in every survey that has checked.

Solve for Weight (kg)

Weight (kg): 76.9958 for BMI 26.642

Standard BMI using metric units.

bmi=\frac{ weight}{\left(\frac{ height}{100}\right)^{2}}

bmiweight / pow(height / 100, 2)

BMI decision comparison

item	value	note
Stress low	6.92	Weight (kg): 20
Conservative	18.17	Weight (kg): 52.5
Downside	21.8	Weight (kg): 63
Base case	24.22	Weight (kg): 70
Upside	26.64	Weight (kg): 77

Visual Analysis1 series8 points

Expanded chart built from the same sensitivity run as the table, so users can read the trend and verify the numbers in one place.

Trend

Upward

Min

6.9204

Max

82.276

Insight

BMI shows an upward pattern, with a visible peak around 237.7778 at 82.276.

Visual response curve for BMI.

Two people, same BMI, different pictures
A 180 cm, 90 kg recreational powerlifter and a 180 cm, 90 kg office worker both compute to BMI 27.8 — "overweight." With the optional body-fat field filled in, the picture splits: 15 % body fat suggests the label is mostly lean mass; 30 % supports the screening result. Same arithmetic, opposite conclusions — which is exactly the calculation's designed limitation.

Why does BMI square the height?
Adolphe Quetelet observed in the 1830s that adult weight scales roughly with height squared, and the index (named BMI by Ancel Keys in 1972) keeps that convention. The scaling is imperfect — real body mass grows a little faster than height², so BMI runs slightly high for tall people and low for short people, one of its known structural biases.

Is a BMI just under 18.5 or just over 25 meaningful?
Boundaries are conventions, not thresholds where risk jumps. Risk curves are continuous; a 25.2 differs trivially from a 24.8. What deserves attention is distance from the healthy range and direction of travel over months, alongside waist size and fitness — not a category flip caused by a heavy breakfast.

Should older adults use the same ranges?
Evidence suggests the lowest-mortality BMI shifts modestly upward past about age 65, and unintentional weight loss is a stronger warning sign in that group than mild overweight. The optional age field here provides context; it does not change the WHO ranges, which remain the reference standard this page reports.

Health tools disclaimer: Educational estimates only, not medical advice, diagnosis, or treatment. For clinical decisions, dosing, or emergencies, follow guidance from US Department of Health & Human Services and a licensed professional in your jurisdiction.

Body mass index from weight (kg) and height (cm).

BMI Calculator turns Weight (kg), Height (cm), Age (optional), and Body fat % (optional) into BMI. Confirm the units and assumptions match your situation before relying on the result.

Enter weight. Use your current measured weight, not an estimate. For accuracy, measure in the morning without clothes.
Enter height. Use a measured height, not remembered height — adults lose 0.5–1 cm per decade after age 30.
Select units. Choose metric (kg/cm) or imperial (lbs/in). The formula is: BMI = weight(kg) / height(m)²
Read your BMI. BMI < 18.5 = Underweight; 18.5–24.9 = Normal; 25–29.9 = Overweight; ≥ 30 = Obese (WHO categories).
Interpret with context. BMI does not distinguish muscle from fat. Athletes, pregnant women, and the elderly need additional metrics (body fat %, waist circumference).

Overwhelm from technical jargon

Start with the basic inputs only — advanced options can be explored once you understand the fundamentals. Important: Don't be discouraged if your results seem unfavorable — these tools help you plan, not judge.

Enter your values, then check the formula, scenarios, and FAQ to confirm the assumptions fit your case. For medical, financial, legal, or safety-critical decisions, treat the output as an estimate and verify it against the relevant professional standard.

World Health Organization. "Body mass index - BMI." WHO Regional Office for Europe, 2024.BMI classification thresholds: underweight <18.5, normal 18.5-24.9, overweight 25-29.9, obese ≥30
Centers for Disease Control and Prevention. "About Child & Teen BMI." CDC, 2024.Pediatric BMI uses age-sex-specific percentiles, not adult thresholds
Mifflin MD, St Jeor ST, et al. "A new predictive equation for resting energy expenditure in healthy individuals." Am J Clin Nutr. 1990;51(2):241-247.BMR formula: 10×weight(kg) + 6.25×height(cm) - 5×age - 161 (female) or +5 (male)
Institute of Medicine. "Weight Gain During Pregnancy: Reexamining the Guidelines." National Academies Press, 2009.Recommended pregnancy weight gain by pre-pregnancy BMI category

When is this health estimation context enough?
Use it when the result only depends on age, sex, height and no local rule changes the interpretation.

What should I record with the result?
Record the input values, reference population, measurement unit, activity estimate, output unit, and rounding rule used in the calculation.

When should I use a specialized modifier?
Use a specialized modifier when measurement units, reference range, age/sex context, and non-diagnostic limits materially changes how the same result should be explained.

Reading the category as a diagnosis. A rugby player at BMI 28 and a sedentary person at BMI 28 carry different risks; BMI screens, it does not diagnose. Clinical assessment adds waist circumference (risk rises above about 102 cm for men, 88 cm for women per NIH guidance), body composition, and metabolic markers.

Using standard cutoffs where population-specific ones apply. 5 kg/m² exist because type 2 diabetes and cardiovascular risk appear at lower BMI in those groups.

BMI Calculator — Body Mass Index

Verification & transparency

Verified methodology

Data & accuracy

Privacy & ethics

Primary output (BMI)

Calculator inputs

Mathematical model

Term Glossary