About the BMI Calculator
Tezmy's BMI Calculator works out your body mass index from your height and weight, in metric (centimetres and kilograms) or US units (feet, inches and pounds). It shows which World Health Organization category you fall into (underweight, healthy weight, overweight or obese) on a simple colour scale, and tells you the healthy weight range for your height. BMI is a quick screening number for adults; it doesn't measure body fat directly, so treat it as a starting point, not a diagnosis.
Updated October 2026
How to use the BMI Calculator
- 1Choose metric (cm, kg) or US units (ft, lb).
- 2Enter your height.
- 3Enter your weight.
- 4Read your BMI, your category and your healthy weight range.
BMI categories for adults
These are the World Health Organization categories for adults aged 18 and over:
- Below 18.5: underweight.
- 18.5 to 24.9: healthy weight.
- 25 to 29.9: overweight.
- 30 or more: obese.
The BMI formula
BMI is your weight in kilograms divided by your height in metres squared. For someone who is 1.70 m tall and weighs 68 kg: 68 ÷ (1.70 × 1.70) = 68 ÷ 2.89 ≈ 23.5, which is in the healthy range. In US units, the formula is weight in pounds × 703 ÷ height in inches squared; the calculator converts for you.
The healthy weight range shown under your result is the weight that would give a BMI between 18.5 and 24.9 at your height.
What BMI doesn't tell you
BMI is a quick screening tool, not a measure of health. It can't tell muscle from fat, so athletes and very muscular people may show as overweight while being perfectly healthy, and older adults may have a normal BMI but little muscle. It also doesn't show where fat is stored: waist size is another useful sign.
Some health organisations use lower cut-offs for people of South Asian, Chinese and other Asian backgrounds, because health risks start at a lower BMI. If your result worries you, talk to a doctor or nurse, who can look at the whole picture.
BMI for children and pregnancy
This calculator is for adults. Children's and teenagers' BMI is judged against growth charts for their age and sex, and BMI isn't used during pregnancy. For these, ask a doctor or use your health service's child BMI tool. For daily goals, the Calorie Calculator comes next, and the Percentage Calculator helps with a target weight change. If you also want a number for daily needs, the Age Calculator gives your exact age, and the Percentage Calculator shows a change in weight as a percent.
Features
- Metric and US units
- WHO adult BMI categories
- Colour scale showing where you are
- Healthy weight range for your height
- Instant results
- Private: nothing is stored
Frequently asked questions
How is BMI calculated?
BMI is your weight in kilograms divided by your height in metres squared. For example, 70 kg ÷ (1.75 m × 1.75 m) = 22.9.
What is a healthy BMI?
For adults, the WHO considers 18.5 to 24.9 a healthy weight. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or more is obese.
Is BMI accurate for everyone?
Not always. Very muscular people can have a high BMI without extra fat, and BMI doesn't reflect age, sex or where fat is stored. Some ethnic groups have different risk thresholds.
Can children use this BMI calculator?
No. Children and teenagers need age- and sex-specific BMI percentiles. Ask a doctor or use a child BMI chart.
Is my data saved?
No. The calculation happens in your browser and nothing you enter is stored or sent anywhere.
How do I calculate BMI in kg and cm?
Choose metric, enter your height in centimetres and weight in kilograms. The calculator converts height to metres and divides your weight by height squared.
What is a healthy weight for my height?
Enter your height and the calculator shows the weight range that gives a healthy BMI of 18.5 to 24.9. It's a general guide, not a personal target.
How many calories should I eat to reach a healthy weight?
Use our Calorie Calculator to estimate the calories you need a day to maintain, lose or gain weight, based on your age, height, weight and activity.