BMI Calculator
Calculate your Body Mass Index (BMI) from height and weight, in metric or imperial units.
Enter your height and weight to instantly calculate your Body Mass Index and see the standard WHO weight category. Works in metric (cm/kg) or imperial (in/lb). Everything is computed in your browser.
| Underweight | < 18.5 |
| Normal | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obese | ≥ 30 |
Choose metric or imperial units, then enter your height and weight — centimeters and kilograms for metric, or inches and pounds for imperial. The calculator instantly returns your BMI value and its WHO weight category, with no sign-up or data upload since everything runs in your browser.
Formula & methodology
Metric: BMI = weight(kg) / height(m)². Imperial: BMI = 703 × weight(lb) / height(in)².
Uses the World Health Organization adult classification: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, 30+ obese.
Worked example
- 70 kg, 175 cm → BMI 22.9 — Normal weight
- 154 lb, 69 in → BMI 22.7 — Normal weight
Assumptions
- BMI uses only height and weight, so it cannot tell how much of your weight is muscle versus fat.
- The standard adult categories assume a fully grown adult; they are not designed for children, teens, pregnant people, or very muscular athletes.
- The formula weight/height² is applied the same way regardless of age, sex, or body frame, even though body composition varies across these groups.
Common mistakes
- Mixing units, such as entering height in inches while weight is in kilograms, which produces a meaningless result.
- Treating a single BMI number as a medical diagnosis rather than a quick screening estimate.
- Forgetting that the WHO categories were derived from population-level data, so they may not reflect an individual's actual health risk.
Frequently asked questions
Is BMI accurate for everyone?
BMI is a simple screening tool and does not distinguish muscle from fat. Athletes, pregnant people, children and the elderly may need other measures.
What is a healthy BMI?
For most adults a BMI between 18.5 and 24.9 is considered the normal range.
Is BMI accurate for muscular people or athletes?
Not always. Muscle is denser than fat, so athletes and bodybuilders often have a high BMI despite low body fat. In these cases, body fat percentage or waist circumference are more informative.
Does BMI differ for men and women or by age?
The standard adult BMI thresholds are the same for men and women and don't adjust for age, though body fat distribution naturally differs between sexes and tends to increase with age at the same BMI.
Can I use BMI for children or teenagers?
No — children and teens should use age- and sex-specific BMI percentile charts instead of the fixed adult categories, since their body composition changes as they grow.
Privacy
All processing happens locally in your browser. Your data is never uploaded.
Disclaimer: This calculator is for general information only and is not medical advice. Consult a healthcare professional about your health.