BMI Calculator
What Is a BMI Calculator?
BMI — Body Mass Index — is the world's most widely used screening measure for weight-related health risk. It combines your height and weight into a single number that places you in one of four standard categories: underweight, healthy weight, overweight or obese. Doctors, insurers, fitness coaches and public health agencies use it because it is quick, needs no equipment, and works reasonably well for most adults.
This free calculator is for anyone who wants a fast, honest read on where they stand: people starting a fitness plan, parents checking a teenager's growth chart context, or anyone who has been told to "watch their weight" and wants a number to watch. It supports both metric (cm/kg) and imperial (feet, inches/pounds) units, shows your category on a colour scale, and tells you the healthy weight range for your exact height.
How to Use This BMI Calculator
- Choose your units. Tap "Metric" for centimetres and kilograms, or "Imperial" for feet, inches and pounds.
- Enter your height. Stand straight against a wall for the most accurate figure — morning height is slightly taller than evening height.
- Enter your weight. Weigh yourself first thing in the morning, after using the bathroom and before breakfast, for consistency.
- Click "Calculate BMI". You will see your BMI, your category badge, the healthy weight range for your height, and the weight that would put you at a BMI of 22 — the middle of the healthy range.
Worked Example: 175 cm and 70 kg
Let us work through the maths so you can see exactly what the tool does. Take a person who is 175 cm tall and weighs 70 kg:
- Convert height to metres: 175 ÷ 100 = 1.75 m
- Square the height: 1.75 × 1.75 = 3.0625
- Divide weight by the square: 70 ÷ 3.0625 = 22.86
A BMI of 22.86 falls in the healthy range (18.5–24.9). The healthy weight range for 1.75 m is 18.5 × 3.0625 = 56.7 kg up to 24.9 × 3.0625 = 76.3 kg, and a BMI of exactly 22 would mean weighing 22 × 3.0625 = 67.4 kg. Try your own numbers in the tool — and switch to imperial units to confirm you get the same answer either way.
Tips for Using Your BMI Result Well
- Track the trend, not a single reading. Recalculate monthly under the same conditions; the direction of change matters more than one number.
- Pair BMI with a waist measurement. Where you carry weight matters — a waist under half your height is a good companion target.
- Muscular? Read it loosely. Strength athletes often land in "overweight" while being very lean; body-fat percentage tells the fuller story.
- Use the healthy range as your goal band. Any weight inside the range shown by the tool is a reasonable target — you do not need to chase the middle.
- Change habits, not just numbers. Sustainable shifts — walking daily, cooking more, sleeping enough — move BMI more reliably than crash diets.
- See a professional for big changes. If your BMI is well outside the healthy range, a doctor or dietitian can check the full picture safely.
Frequently Asked Questions
What are the BMI categories?
The standard adult categories are: under 18.5 underweight, 18.5–24.9 healthy weight, 25–29.9 overweight, and 30 or above obese. These cut-offs come from large population studies linking BMI ranges to health risk, and they are used by health authorities worldwide.
Is BMI accurate for athletes and muscular people?
Not always. BMI cannot tell muscle apart from fat, so people with a lot of muscle — rugby players, weightlifters, manual workers — can score as overweight or even obese while having low body fat. For them, waist circumference or body-fat percentage is a better guide.
Does BMI work the same for children?
No — children's BMI is interpreted against age-and-sex percentile charts, because healthy BMI changes as children grow. This calculator uses the adult categories, so it is not suitable for under-18s. Paediatricians use dedicated growth charts instead.
What is a healthy BMI to aim for?
The healthy range is 18.5–24.9, and many guidelines point to the low-20s as a sweet spot — the tool shows the weight for a BMI of 22 as a reference. But any weight inside your personal healthy range is fine; the best target is one you can maintain comfortably.
How often should I check my BMI?
Once a month is plenty. Weight fluctuates daily with food, water and hormones, so daily checks mostly add noise. Weigh under consistent conditions — same time of day, similar clothing — and watch the trend over several months.