About the BMI Calculator
This BMI calculator works out your body mass index — your weight in kilograms divided by the square of your height in metres — and tells you which adult weight category it falls in: underweight, healthy weight, overweight or one of the three obesity classes. It accepts pounds with feet and inches, or kilograms with centimetres.
Alongside the number itself you get the healthy weight range for your exact height (BMI 18.5 to 24.9), how far you are from that range, your BMI Prime and a table showing the weight that corresponds to each category boundary. That makes it useful for setting a realistic goal weight or checking a number your doctor mentioned.
The adult cut-offs used here are the standard WHO and CDC ones and apply to people aged 20 and over. BMI is a screening measure, not a diagnosis: it does not separate muscle from fat, so very muscular people can score as overweight. Children and teens need age- and sex-specific percentiles instead.
With the default inputs, the your bmi is 24.4 kg/m². Change any value above to recalculate instantly.
How to use the bmi calculator
- 1Choose US or metric units.
- 2Enter your height in feet and inches, or centimetres.
- 3Enter your current weight.
- 4Read your BMI and weight category.
- 5Check the healthy weight range and table to set a realistic target.
Formula and method
Body mass index divides weight by the square of height. In metric units that is kilograms over metres squared; in US units multiply pounds by 703 and divide by inches squared, which gives the same answer. This calculator converts everything to metric internally (1 lb = 0.45359237 kg, 1 in = 2.54 cm) so both unit systems agree exactly.
The healthy weight range is found by rearranging the formula: weight = BMI × height². Plugging in 18.5 and 24.9 gives the lightest and heaviest weights that count as a healthy BMI for your height. BMI Prime is simply BMI ÷ 25, so values above 1.0 are in the overweight range or higher.
- BMI
- Body mass index, kg/m²
- weight
- Body weight in kilograms (or pounds with the 703 factor)
- height
- Height in metres (or inches with the 703 factor)
Worked examples
5 ft 10 in, 170 lb
5 ft 10 in is 70 inches (1.778 m) and 170 lb is 77.11 kg. 77.11 ÷ 1.778² = 24.4, just inside the healthy range. At that height a BMI of 18.5–24.9 means weighing roughly 128.9 to 173.5 lb.
Metric: 165 cm, 82 kg
82 ÷ 1.65² = 82 ÷ 2.7225 = 30.1, which is obesity class 1. A healthy BMI at 165 cm is 50.4 to 67.8 kg, so reaching the top of the healthy range means losing about 14.2 kg.
5 ft 4 in, 105 lb
105 lb at 64 inches gives 703 × 105 ÷ 64² ≈ 18.0, slightly below 18.5. The lower edge of the healthy range at this height is about 107.8 lb, so a gain of roughly 2.8 lb reaches it.
Frequently asked questions
What is a healthy BMI for adults?+
For adults aged 20 and over, a BMI from 18.5 to 24.9 is classed as healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight and 30 or higher is obesity, which is split into classes 1 (30–34.9), 2 (35–39.9) and 3 (40+).
Is BMI different for men and women?+
No. Adult BMI uses the same formula and the same cut-offs for men and women. Women tend to carry more body fat at the same BMI, which is one reason BMI is only a screening tool and not a measure of body fat.
Is BMI accurate for muscular people?+
Not very. BMI cannot tell muscle from fat, so athletes and people who lift weights often land in the overweight range while having low body fat. A body fat or waist-to-height measurement gives a better picture for them.
Can I use this BMI calculator for children?+
No. For people aged 2 to 19, BMI has to be compared with growth charts for the same age and sex and expressed as a percentile. Use a child BMI calculator that applies the CDC growth charts instead.
How do I calculate BMI by hand in pounds and inches?+
Multiply your weight in pounds by 703, then divide by your height in inches squared. For example, 150 lb at 66 inches is 703 × 150 ÷ 4,356 ≈ 24.2.
Do Asian adults use different BMI cut-offs?+
Some health bodies, including the WHO for public-health action, suggest lower thresholds for Asian populations because health risks rise at lower BMIs — often 23 for increased risk and 27.5 for high risk. This calculator shows the standard international categories.
This tool gives general estimates and is not medical advice. Talk to a doctor or qualified professional about your health, diet or training.