Body Mass Index is weight in kilograms divided by height in metres squared (kg/m²). It is a simple population screening metric, not a direct measure of fat, muscle, or metabolic health.

Is BMI a medical diagnosis?

No. BMI alone does not diagnose illness. Clinicians may also consider waist circumference, blood pressure, lipids, glucose, fitness, medications, and personal history. This calculator is informational, not medical advice.

Why can BMI misclassify athletes or people with high muscle mass?

Muscle and bone are denser than fat. High lean mass can raise weight—and therefore BMI—without excess adiposity. Imaging or other body-composition methods tell a different story than BMI alone.

Do children use the same BMI cut-offs as adults?

No. Pediatric interpretation uses growth-chart percentiles for age and sex. This tool follows common adult category bands unless a page note states otherwise. Ask a pediatric clinician about child measurements.

What about pregnancy, edema, or recent illness?

Temporary fluid shifts, pregnancy-related weight change, and some medical conditions alter body weight without reflecting usual body-fat status. Clinical context is essential; do not self-manage those situations from BMI alone.

Which units does the calculator accept?

Metric (cm, kg) and common imperial (ft/in, lb) inputs are supported. Internally the math still uses kg and metres. Convert carefully if your tape and scale disagree on systems.

Why does a small height change move BMI a lot?

Height is squared in the denominator. Measuring 1 cm short can noticeably inflate BMI. Stand tall with consistent footwear rules when comparing readings over time.

Are WHO or CDC category labels the same everywhere?

Core adult thresholds are widely shared, but some regions publish additional guidance (for example differing Asian BMI action points in certain clinical documents). Always read the labels shown in the tool and your clinician’s guidance.

Can I improve health by “living at a BMI number”?

Sustainable habits, medical screening, and individualized goals usually matter more than chasing a single index. Sudden restrictive practices can be harmful—seek professional support for weight or nutrition changes.

Does BMI differ by sex?

The kg/m² formula itself is the same. Category interpretation and health risk associations can still differ by sex, age, and other factors studied in epidemiology—another reason BMI is only one input.

How often should I recalculate?

Recalculate when height is remeasured (especially adolescents until growth finishes) or when weight changes enough to matter for your tracking. Day-to-day scale noise is normal.

Is my height and weight data private?

Yes for this tool: inputs are processed in your browser and are not sent to our servers as a health record.

BMI Calculator

Body Mass Index combines weight and height into one screening number used widely in public-health charts and forms. This BMI calculator accepts metric or imperial inputs, converts them consistently, and reports kg/m² with commonly cited adult category ranges. BMI is a population tool—it does not diagnose disease, measure body fat directly, or replace clinical judgment. Athletes with high muscle mass, older adults, pregnancy, and many medical situations need fuller assessment. Use this page for informational comparison only, and talk with a healthcare professional about personal health risks or goals.

Weight (kg)Height (cm)

BMI

Informational only; verify critical results independently.

How to use

Measure height and weight with reasonable care; small height errors change BMI more than many people expect because height is squared.
Enter height in centimetres or feet and inches, and weight in kilograms or pounds, using the mode that matches your measurements.
Confirm you did not mix systems—for example entering pounds while thinking in kilograms, or metres while the field expects centimetres.
Compute BMI as weight divided by height squared after converting to kilograms and metres.
Read the numeric BMI and the broad adult category band shown on the page (underweight through obesity classes, as labeled).
If you switch units, re-enter values from scratch so leftover fields do not mix leftover imperial and metric digits.
Compare the number to prior measurements taken under similar conditions rather than to a single “ideal” marketing claim.
Remember that muscle, bone, limb proportion, ethnicity-linked risk research, and waist circumference can change how clinicians interpret the same BMI.
Do not use this adult calculator for young children; pediatric assessment uses age- and sex-specific percentiles on dedicated charts.
Treat the result as one screening snapshot for information—not a diagnosis—and seek medical advice for personal health decisions.

Examples

180 cm and 75 kg → BMI = 75 ÷ (1.80²) = 23.15 (often described as a healthy weight band for adults).
5 ft 10 in (70 in) and 180 lb → convert to ~1.78 m and ~81.6 kg → BMI ≈ 25.8 (near overweight threshold).
Boundary check: at 1.70 m, weight 72.25 kg yields BMI = 25.0 exactly at a common adult overweight cut-off.
Same person metric vs imperial: 160 cm / 60 kg (BMI 23.4) should match ~5 ft 3 in / 132 lb within rounding.
Muscular athlete at 185 cm / 95 kg → BMI ≈ 27.8 may sit in an overweight band despite low body fat—category limitation example.
Lower height sensitivity: 1.60 m at 70 kg → BMI 27.3; losing 3 kg to 67 kg → BMI 26.2.
Higher height: 1.90 m at 85 kg → BMI 23.5; at 100 kg → BMI 27.7.
Underweight screen example: 1.65 m at 48 kg → BMI ≈ 17.6.
Obesity class illustration (informational labels only): 1.75 m at 110 kg → BMI ≈ 35.9.
Unit pitfall: entering 180 as pounds instead of kilograms for a metric height produces a falsely low BMI—always verify units.

FAQ

What is BMI?: Body Mass Index is weight in kilograms divided by height in metres squared (kg/m²). It is a simple population screening metric, not a direct measure of fat, muscle, or metabolic health.
Is BMI a medical diagnosis?: No. BMI alone does not diagnose illness. Clinicians may also consider waist circumference, blood pressure, lipids, glucose, fitness, medications, and personal history. This calculator is informational, not medical advice.
Why can BMI misclassify athletes or people with high muscle mass?: Muscle and bone are denser than fat. High lean mass can raise weight—and therefore BMI—without excess adiposity. Imaging or other body-composition methods tell a different story than BMI alone.
Do children use the same BMI cut-offs as adults?: No. Pediatric interpretation uses growth-chart percentiles for age and sex. This tool follows common adult category bands unless a page note states otherwise. Ask a pediatric clinician about child measurements.
What about pregnancy, edema, or recent illness?: Temporary fluid shifts, pregnancy-related weight change, and some medical conditions alter body weight without reflecting usual body-fat status. Clinical context is essential; do not self-manage those situations from BMI alone.
Which units does the calculator accept?: Metric (cm, kg) and common imperial (ft/in, lb) inputs are supported. Internally the math still uses kg and metres. Convert carefully if your tape and scale disagree on systems.
Why does a small height change move BMI a lot?: Height is squared in the denominator. Measuring 1 cm short can noticeably inflate BMI. Stand tall with consistent footwear rules when comparing readings over time.
Are WHO or CDC category labels the same everywhere?: Core adult thresholds are widely shared, but some regions publish additional guidance (for example differing Asian BMI action points in certain clinical documents). Always read the labels shown in the tool and your clinician’s guidance.
Can I improve health by “living at a BMI number”?: Sustainable habits, medical screening, and individualized goals usually matter more than chasing a single index. Sudden restrictive practices can be harmful—seek professional support for weight or nutrition changes.
Does BMI differ by sex?: The kg/m² formula itself is the same. Category interpretation and health risk associations can still differ by sex, age, and other factors studied in epidemiology—another reason BMI is only one input.
How often should I recalculate?: Recalculate when height is remeasured (especially adolescents until growth finishes) or when weight changes enough to matter for your tracking. Day-to-day scale noise is normal.
Is my height and weight data private?: Yes for this tool: inputs are processed in your browser and are not sent to our servers as a health record.

Formula / Method

BMI = weight (kg) ÷ [height (m)]². Imperial path: convert lb to kg (÷2.20462) and inches to metres (×0.0254), then apply the same formula. Adult category bands shown on the page follow commonly published cut-offs for informational labeling only.

Assumptions & Limitations

Informational screening only—not medical advice or a diagnosis. Adult calculator; not for pediatric percentile assessment. Does not measure body fat, fitness, or disease risk directly. Misclassification risk rises for athletes, older adults, pregnancy, and certain ethnic or clinical contexts. Seek professional care for personal decisions.

Related guides

BMI and Health Metrics: What They Mean and When to Use Them
Understand adult BMI categories, limits of the metric, and how BMR/TDEE estimates work—informational tools, not medical advice.

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Last updated: 2026-07-13

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