Underweight
A low BMI can flag too-low weight for height. It is a screening cue, not a diagnosis — talk with a clinician if this is unexpected.
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BMI Calculator
Free BMI calculator (body mass index calculator) to calculate BMI from height and weight in seconds. See your score, WHO or Asian category, healthy weight range, and a clear live visual.
Enter height and weight to highlight your BMI band.
How it works
How to calculate BMI
A body mass index calculator uses one clear equation. Whether you need a BMI calculator metric or a BMI calculator imperial, the math maps to the same adult score.
BMI formula / equation
BMI = Weight (kg) ÷ Height (m)²
Example: 70 kg ÷ 1.70 m² = 24.2
- Imperial shortcut: BMI = 703 × lb ÷ height(in)²
- Adult WHO healthy band is usually 18.5–24.9
- This tool also shows a healthy weight range for your height
Measure height without shoes. Use cm, m, inches, or feet and inches — the calculator converts for you.
Visual classification
BMI chart and categories
Use this BMI chart to map your number. Adult WHO bands are the default; Asian adult cut-offs are also shown because overweight and obesity can start at lower BMI in some populations.
WHO adult BMI
< 18.5Underweight
18.5–24.9Healthy
25.0–29.9Overweight
≥ 30Obesity
Asian adult BMI
< 18.5Underweight
18.5–22.9Healthy
23.0–24.9Overweight
≥ 25Obesity
Healthy / normal
The usual healthy BMI zone on WHO adult charts. Many people treat this as the target range for a BMI calculator result.
Overweight
Standard overweight BMI band. On Asian charts this zone often starts at 23. Lifestyle context and waist measures still matter.
Obesity
WHO obesity starts at 30 (class I 30–34.9, class II 35–39.9, class III ≥ 40). Educational only — not a medical label.
Adult BMI charts are for most people aged 20+. Children and teens need BMI-for-age percentiles, not this adult calculator.
Reference tables
BMI table for men, women, and by age
People often look for a BMI table, BMI for men, and BMI for women. Adult WHO cut-offs are shared by sex; age still changes how you should interpret the number.
| Category | BMI | What it usually means |
|---|---|---|
| Underweight | < 18.5 | Weight may be low for height |
| Healthy / normal | 18.5 – 24.9 | Common adult target band |
| Overweight | 25.0 – 29.9 | Higher weight for height |
| Obesity class I | 30.0 – 34.9 | Obesity, first class |
| Obesity class II | 35.0 – 39.9 | Obesity, second class |
| Obesity class III | ≥ 40.0 | Severe / class III obesity |
| Age context | What to know | Practical tip |
|---|---|---|
| Children / teens | Adult BMI charts do not apply. Clinicians use BMI-for-age percentiles. | Skip adult risk labels; ask a pediatric clinician. |
| Adults 20–64 | Most online BMI calculators and WHO tables target this group. | Track trend plus waist, not one weigh-in day. |
| Adults 65+ | A slightly higher BMI can be common; muscle loss also changes the picture. | Pair BMI with function, appetite, and clinical review. |
| Pregnancy | Gestational weight is not interpreted with standard adult BMI goals. | Use clinician guidance, not calculator categories. |
Men, women & limits
BMI for men and women
Sex-specific adult WHO cut-offs are the same. The calculator still helps both groups because healthy weight range depends on your height, not a one-size target weight.
BMI for men
Adult men use the same 18.5–24.9 healthy band. A high BMI in muscular men can overstate fat. Pair this tool with a waist to height ratio calculator for central fat context.
BMI for women
Adult women also use 18.5–24.9 on the WHO chart. Body fat percentage is often higher at the same BMI, so the number is a screen — not a complete health score.
Healthy weight target
This BMI calculator shows the weight range that keeps BMI inside the selected healthy band for your height — a practical goal besides the raw score.
Why use a body mass index calculator?
BMI (body mass index) compares weight with height. A BMI calculator is useful as a fast screening number — especially when you want a simple category such as underweight, healthy, overweight, or obesity — but it does not measure fat, muscle, or waist shape.
Whether you arrived from body mass index calculator, BMI calculator metric, or BMI calculator imperial, this page does the same job: convert units, apply the formula, classify the result, and explain the number in plain language.
How to calculate BMI correctly
Metric: convert height to meters, then use BMI = kg ÷ m². Example: 70 kg and 170 cm → 70 ÷ 1.70² = 24.2. Imperial: BMI = 703 × lb ÷ in². Measure height without shoes and use a consistent morning weight when possible.
Healthy, overweight, and obesity bands
On the WHO adult chart, healthy BMI is 18.5–24.9, overweight BMI starts at 25, and obesity starts at 30. Class I is 30–34.9, class II 35–39.9, and class III 40+. Many Asian adult guides treat overweight from 23 and obesity from 25 — switch the chart toggle above to compare.
BMI vs waist to height ratio
BMI estimates weight for height. Waist to height ratio estimates central shape. Someone can have a “normal” BMI with a higher waist, or a higher BMI with more muscle. For a second screen, use our free waist to height ratio calculator and waist to hip ratio calculator.
What this tool does not do
It is not a child BMI percentile chart, a body-fat scan, or medical advice. Athletes, pregnancy, edema, and some ethnic groups need extra context. Use the result as education, then confirm personal decisions with a healthcare professional.
FAQ
BMI calculator FAQ
What is BMI (body mass index)?
BMI is weight in kilograms divided by height in meters squared. It is a screening ratio, not a direct fat measurement.
How do you calculate BMI?
BMI = kg ÷ (m × m). Example: 70 ÷ 1.70² = 24.2. Imperial: 703 × lb ÷ (in × in). Or use the free calculator above.
What is a healthy BMI?
For most adults on the WHO chart, 18.5–24.9 is the healthy or normal band. Under 18.5 is underweight; 25+ is overweight or obesity.
Is BMI different for men and women?
Adult WHO cut-offs are the same. Body composition still differs, so treat BMI as a starting point rather than a complete health grade.
What BMI is overweight or obese?
WHO: overweight 25–29.9, obesity 30+. Many Asian adult charts: overweight from 23 and obesity from 25.
Why can muscular people have a high BMI?
BMI does not split muscle from fat. High lean mass can raise BMI. Pair it with waist measures or clinical assessment.
Related calculators & trust
- Transparent math: BMI = kg ÷ m² (or 703 × lb ÷ in²)
- Metric, imperial, and stone / pound support
- WHO and Asian adult classification charts
- Healthy weight range for your height
- Runs in your browser — no account required
Educational use only. This BMI calculator does not replace medical advice. Read our Disclaimer and Terms and Conditions.