What is the BMI Calculator?
Body Mass Index (BMI) compares your weight with your height to give a single number. Doctors use it as a quick screening tool to see whether a person may be underweight, at a healthy weight, overweight or obese.
Our BMI calculator accepts kilograms and centimetres or pounds, feet and inches. Along with your BMI it shows your weight category on a colour scale and the weight range that would put you in the healthy band for your height. BMI does not measure body fat directly, so treat it as a starting point and speak to a doctor for personal advice.
How to use the BMI Calculator
- Choose Metric (kg, cm) or Imperial (lb, ft and in).
- Enter your weight and height.
- Read your BMI and category in the result box.
- Check the healthy weight range shown for your height.
Formula
BMI = weight (kg) ÷ height (m)² · Imperial: BMI = 703 × weight (lb) ÷ height (in)²
Example
A person who weighs 70 kg and is 170 cm tall has a BMI of 70 ÷ (1.70 × 1.70) = 24.2, which is in the healthy range. Their healthy weight range is about 53.5 kg to 72 kg.
BMI chart for adults (WHO)
| BMI | Category |
|---|---|
| Below 16 | Severely underweight |
| 16 – 18.4 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25 – 29.9 | Overweight |
| 30 – 34.9 | Obese class I |
| 35 – 39.9 | Obese class II |
| 40 and above | Obese class III |
Limitations of BMI
BMI cannot tell muscle from fat, so athletes may show a high BMI while being fit. It is less reliable for older adults, pregnant women and children; children and teenagers need age- and sex-specific BMI percentiles. Some health bodies suggest lower cut-offs for South Asian adults, for example treating 23 and above as overweight, because health risks rise at lower BMI levels.
Risks of being outside the healthy range
Overweight and obesity
Higher BMI is linked with type 2 diabetes, high blood pressure, heart disease and joint problems.
Underweight
Low BMI can be linked with weak immunity, fatigue, bone loss and nutrient deficiencies.
You may also need
People who use the BMI Calculator often need these related tools too:
- Age Calculator: Find your exact age in years, months and days from your date of birth, plus the total days, weeks and hours you have lived and how long until your next birthday. Useful for forms, admissions and job applications that ask for age on a specific date.
- Percentage Calculator: Four percentage calculators on one page: X% of Y, X is what percent of Y, percentage increase or decrease, and adding or removing a percentage. Ideal for marks, discounts, salary raises and price changes.
- Discount Calculator: Work out the final price after a percentage discount and exactly how much you save. Handles extra discounts like "flat 50% + 20% off" and adds sales tax if needed.
- Loan Calculator: See your monthly loan payment, total interest and payoff date, with a yearly and monthly amortization schedule. Works for personal, car, home and business loans.
Frequently asked questions
What is a healthy BMI?
For most adults a BMI from 18.5 to 24.9 is considered healthy by the World Health Organization.
How do I calculate BMI in feet and inches?
Choose Imperial, enter your weight in pounds and your height in feet and inches. The calculator converts everything for you.
Is BMI accurate for athletes and bodybuilders?
Not always. Muscle weighs more than fat, so very muscular people can have a high BMI without excess body fat.
Is BMI different for men and women?
The adult BMI categories are the same for men and women, although body fat at the same BMI usually differs.
Can children use this BMI calculator?
The categories here are for adults aged 18 and over. Children need BMI-for-age percentile charts.
What is my ideal weight?
The calculator shows the weight range that gives a BMI between 18.5 and 24.9 for your height, which is a reasonable target range for most adults.
Is the BMI Calculator free to use?
Yes. The BMI Calculator on Custom Converter is completely free, with no sign-up, no daily limit and no watermark.
Does the BMI Calculator work on mobile phones?
Yes. It is built mobile-first and works on Android phones, iPhones, tablets and computers in any modern browser, with no app to install.