BMI Calculator
Body mass index (BMI) compares your weight with your height and is widely used as a quick screening measure. It cannot tell you about your fitness, muscle mass or health, but it is a simple starting point for a conversation with a health professional. This calculator works in metric or imperial units and also shows the weight range that corresponds to the healthy BMI band for your height.
How to use the bmi calculator
- Choose metric (kilograms and centimetres) or imperial (pounds and inches).
- Enter your weight and height. For imperial height, use total inches, for example 5 ft 9 in = 69.
- Read your BMI, the category and the healthy weight range.
Formula
BMI = weight (kg) ÷ height (m)². In imperial units, BMI = 703 × weight (lb) ÷ height (in)². The World Health Organization’s adult categories are: below 18.5 underweight, 18.5 to 24.9 healthy weight, 25 to 29.9 overweight and 30 or more in the obesity range.
Worked examples
A metric example
70 kg at 175 cm: 1.75² = 3.0625, and 70 ÷ 3.0625 = 22.86, which falls in the healthy range.
An imperial example
154 lb at 69 inches: 154 × 0.4536 = 69.9 kg and 69 × 2.54 = 175.3 cm, giving a BMI of about 22.7.
What BMI does and does not tell you
Adult BMI categories (WHO)
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obesity range |
Strengths
BMI is quick, free and uses only two measurements. It is useful for spotting general population trends and as a rough first screen.
Limits
- It does not separate muscle from fat, so athletes can score high.
- It does not show where fat is stored, which matters for health.
- Thresholds can be less accurate for some ethnic groups, older adults and those who are pregnant.
- It is not designed for children or teenagers, who use growth charts.
Better together
Doctors usually combine BMI with waist measurement, blood tests, activity level and family history. If your result concerns you, speak to a healthcare professional. This tool is for general information only and is not medical advice.
Practice problems
Try these yourself first, then check your answer. The answers come from the calculator above.
- A person weighs 82 kg and is 180 cm tall. Find the BMI.
Show answer
BMI: 25.31 · Category (adult, WHO ranges): Overweight
- A person weighs 130 lb and is 64 inches tall.
Show answer
BMI: 22.31 · Category (adult, WHO ranges): Healthy weight
Common mistakes to avoid
- Using this for children and teenagers, whose BMI is interpreted with age- and sex-specific charts.
- Treating BMI as a diagnosis. It does not distinguish muscle from fat.
- Mixing units, such as pounds with centimetres.
Frequently asked questions
What is a healthy BMI?
For most adults, the WHO defines 18.5 to 24.9 as the healthy weight range.
Is BMI accurate for athletes?
Not always. Muscular people can have a high BMI without excess body fat.
Should I worry about my result?
BMI is only a screening tool. Talk to a doctor or dietitian about your health; this page is not medical advice.
Does BMI apply to children?
No. Children’s BMI is compared with growth charts for their age and sex.
Reviewed September 26, 2026 by the SolveCalcPro editorial team. Found a mistake? Tell us; see our editorial policy.