What is BMI? How do you calculate body mass index?
Body mass index (BMI) is weight ÷ height² (kg/m²). This BMI calculator — a free body mass index calculator — lets you calculate BMI with US, metric or mixed units so you can calculate my BMI online in seconds. The math is identical for a BMI calculator male or BMI calculator female; sex does not change how BMI is calculated.
Why use a BMI calculator online?
A free BMI calculator is a fast screening step used in references from the CDC BMI calculator guidance, BMI calculator NHS materials, and BMI calculator Mayo Clinic education pages. BMI is not a diagnosis — clinicians still review blood pressure, lipids, waist size and comorbidities. Ask is BMI calculator accurate? It correlates with adiposity for most adults, but BMI calculator vs body fat is not a 1:1 swap — does BMI calculate muscle mass? No. Athletes may look “overweight” on the chart while lean. On this site, height and weight also feed the body surface area calculator, creatinine clearance calculator and eGFR calculator.
BMI bands at a glance
BMI formula (metric and imperial)
To calculate BMI by hand — or check how to calculate BMI with height and weight — convert to kilograms and meters, or use the imperial shortcut for BMI calculator lbs and inches workflows. This free BMI calculator online does both: BMI calculator metric (kg/cm) and BMI calculator imperial (ft/in + lb).
Example: 70 kg and 1.70 m → BMI = 70 ÷ 2.89 ≈ 24.2 kg/m². Same BMI calculation formula for a BMI calculator for men or BMI calculator for women.
Example: 160 lb and 70 in (5′10″) → BMI ≈ 703 × 160 ÷ 4900 ≈ 23.0 kg/m² — a common calculate my BMI check.
BMI chart calculator (imperial height × weight)
Use this BMI chart to look up body mass index from height (ft/in) and weight (lbs) at a glance — the same idea as a printable BMI chart calculator. Colors follow WHO adult BMI categories: underweight, healthy / normal BMI, overweight, and obese class I–III. Prefer the interactive tool above for exact values; the grid helps you see patterns (for example a healthy BMI calculator target band in green).
On mobile: scroll the chart sideways — height stays pinned on the left.
Tip: after you calculate BMI above, compare your result to this chart. For child BMI calculator / pediatric BMI / teen BMI calculator use CDC percentiles — not this adult grid. BMI calculator for seniors still uses the same adult equation, but interpret results with muscle mass and frailty in mind.
BMI table for adults (WHO)
World Health Organization adult BMI categories — used for men and women (typically age 20+).
| Classification | BMI |
|---|---|
| Severe Thinness | < 16 |
| Moderate Thinness | 16 – 17 |
| Mild Thinness | 17 – 18.5 |
| Normal | 18.5 – 25 |
| Overweight | 25 – 30 |
| Obese I | 30 – 35 |
| Obese II | 35 – 40 |
| Obese III | > 40 |
Asian BMI cut-offs
Asia-Pacific adult cut-offs often flag overweight earlier than global WHO bands (overweight from BMI 23).
| Classification | BMI |
|---|---|
| Underweight | < 18.5 |
| Normal | 18.5 – 22.9 |
| Overweight | 23 – 24.9 |
| Obese | ≥ 25 |
BMI table for children and teens (CDC)
CDC BMI-for-age percentiles for ages 2–20 — not fixed adult bands. This calculator warns when age is under 20.
| Category | Percentile |
|---|---|
| Underweight | < 5th |
| Healthy weight | 5th – 85th |
| At risk of overweight | 85th – 95th |
| Overweight | > 95th |
Is a BMI calculator accurate? BMI vs body fat
How accurate is BMI calculator output? For most adults it is a useful screen for underweight / overweight / obesity, which is what BMI is used for in clinics and public health. It still does not measure body fat or muscle directly. Pair results with waist measures or composition testing when decisions depend on adiposity — especially for muscular adults, pregnancy, edema, or sarcopenia.
BMI Prime and Ponderal Index
BMI Prime divides your BMI by 25 (the WHO overweight threshold). A Prime of 0.92 means BMI 23 — still in the normal band. Ponderal Index (PI) uses weight ÷ height³ (kg/m³) and can be easier to interpret when someone is very tall or very short. This calculator reports both alongside a healthy weight range for your height (WHO 18.5–24.9 and Asian 18.5–23).
FAQ
What is BMI (body mass index)?
BMI is weight in kilograms divided by height in meters squared (kg/m²). It screens for underweight, overweight and obesity at the population level.
How do you calculate BMI?
Metric: BMI = kg ÷ m². Imperial: BMI ≈ 703 × lb ÷ in². Use the calculator above to convert stones, feet/inches or mixed units automatically.
Is the BMI formula the same for men and women?
Yes — men and women use identical math. Sex-specific charts apply only to pediatric BMI-for-age percentiles, not the adult equation.
What is a healthy BMI for adults?
WHO and many US/UK references use 18.5–24.9 kg/m² as normal for adults 20+. Individual goals may differ with age, illness or pregnancy.
What are Asian BMI cut-offs?
Asia-Pacific guidance often marks overweight from BMI 23 and obesity from 25, with normal weight 18.5–22.9. Toggle “Asian cut-offs” in the tool to match.
How is BMI used for children and teens?
Ages 2–19 use CDC/WHO BMI-for-age percentiles on growth charts — not fixed adult bands. Plot percentiles before labeling obesity or underweight.
Does BMI measure body fat or muscle?
No. It cannot separate muscle from fat. Athletes with high lean mass may have high BMI; add waist measures or body composition tests when it matters clinically.
What is BMI Prime?
BMI Prime = BMI ÷ 25. Values below 1.0 are under the WHO overweight line; 1.0 equals BMI 25 exactly.
What is Ponderal Index?
PI = weight (kg) ÷ height (m)³, in kg/m³. Some clinicians prefer PI when height is far from average.
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User Reviews
4.8 / 5 from 3 recent users of this BMI calculator
WHO vs Asian toggle is handy for clinic intake. Imperial height fields work well on my phone.
Healthy weight band and BMI Prime save me from re-typing the formula during counseling sessions.
Clear categories and the live formula breakdown. Still use CDC charts for pediatrics — as the page notes.
For dosing and filtration after BMI, continue with the body surface area calculator, creatinine clearance calculator and eGFR calculator.