BMI Calculator
Body mass index (BMI) compares your weight with your height and is widely used as a quick screening measure for adults. It cannot tell you about your fitness, muscle mass, where you carry fat or your overall health, but it is a simple starting point for a conversation with a health professional. This calculator works in metric or imperial units (pounds, feet and inches), shows your WHO category and BMI Prime, and calculates the weight range that falls inside the healthy BMI band for your exact height.
How to use the bmi calculator
- Choose metric (kilograms and centimetres) or imperial (pounds, feet and inches).
- Enter your weight and height. For imperial height, enter feet in the height box and the remaining inches in the inches box — 5 ft 9 in is height 5, inches 9.
- Read your BMI, the category and the healthy weight range for your height.
- Use the result as one data point, not a verdict, and talk to a clinician about anything that worries you.
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; 30 to 34.9 obesity class 1; 35 to 39.9 class 2; and 40 or more class 3. BMI Prime is BMI ÷ 25, so a value of 1.0 sits at the overweight boundary.
Worked examples
A metric example
70 kg at 175 cm: 1.75² = 3.0625, and 70 ÷ 3.0625 = 22.9, a healthy weight result. Healthy weight range for that height: 56.66 kg – 76.26 kg.
An imperial example
154 lb at 5 ft 9 in (69 inches): 703 × 154 ÷ 69² = 22.7, healthy range 125.3 lb – 168.6 lb.
An above-range example
220 lb at 5 ft 8 in gives a BMI of 33.5 (Obesity class 1), which is 56.24 lb above the upper limit.
Reading your BMI result
WHO adult BMI categories
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obesity class 1 |
| 35.0 – 39.9 | Obesity class 2 |
| 40.0 and above | Obesity class 3 |
Healthy weight range by height
| Height | Healthy range |
|---|---|
| 5 ft 0 in (152 cm) | 94.73 lb – 127.5 lb |
| 5 ft 6 in (168 cm) | 114.6 lb – 154.3 lb |
| 6 ft 0 in (183 cm) | 136.4 lb – 183.6 lb |
What BMI does not tell you
BMI ignores muscle, bone density and where fat is stored. Two people with the same BMI can have very different health profiles, and adult cut-offs differ for children, older adults, athletes and some ethnic groups. Use BMI as a screening starting point, then consider waist circumference, fitness, diet and professional advice. For energy balance, see the calorie calculator, and for the method read how to calculate BMI.
Practice problems
Try these yourself first, then check your answer. The answers come from the calculator above.
- A person weighs 82 kg and is 178 cm tall. What is their BMI and category?
Show answer
BMI: 25.9 · Category (adult WHO ranges): Overweight
- A person weighs 180 lb and is 5 ft 10 in tall. What is their BMI?
Show answer
BMI: 25.8 · Category (adult WHO ranges): Overweight
Common mistakes to avoid
- Using this for children and teenagers, whose BMI is interpreted with age- and sex-specific growth charts.
- Treating BMI as a diagnosis. It does not distinguish muscle from fat, bone density or fat distribution.
- Mixing units, such as pounds with centimetres, or typing total inches into the feet box. Check the unit setting and use feet plus inches.
- Applying adult cut-offs to every population without context. Some health bodies recommend lower thresholds for people of South Asian and some other ancestries.
- Chasing a single number. Waist size, fitness, diet and blood tests tell you more than BMI alone.
Frequently asked questions
What is a healthy BMI?
For most adults, the WHO defines 18.5 to 24.9 as the healthy weight range. Health bodies such as the NHS use the same bands.
How do I calculate BMI in pounds and inches?
Multiply your weight in pounds by 703 and divide by your height in inches squared. For 154 lb and 69 in: 703 × 154 ÷ 4,761 = 22.7.
Is BMI accurate for athletes or muscular people?
Not always. Muscle weighs more than fat, so a very muscular person can have a high BMI without excess body fat. BMI is a screening tool, not a body-composition test.
What is BMI Prime?
BMI Prime is your BMI divided by 25, the upper limit of the healthy range. Below 0.74 is underweight; 0.74–1.0 healthy; above 1.0 overweight.
Does BMI apply to children?
No. Children’s BMI is compared with growth charts for their age and sex, usually as a percentile, by a paediatric professional.
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.
Sources and further reading
- World Health Organization — Obesity and overweight fact sheet
- NHS — BMI healthy weight calculator and categories
- NIH NHLBI — Body mass index tables
Reviewed September 26, 2026 by the SolveCalcPro editorial team. Found a mistake? Tell us; see our editorial policy.