BMI Calculator
By Sofia Andersen · Last updated 15 October 2026
A doctor’s office, a gym induction, an insurance form. BMI turns up in all three, and most people meet it without anyone explaining what it is. Here is the short version. It takes your weight and your height, does one division, and hands you a number. That number puts you in a band. The band is a starting point, not a verdict.
Enter your numbers
Result
General information only. This is not medical advice, a diagnosis, or treatment. If weight or health is on your mind, talk with a qualified health professional. Urgent symptoms need urgent care, not a calculator.
The one number people get wrong
Pick metric or imperial, then enter your height and weight. The calculator shows your BMI right away, plus the weight range that would put your BMI between 18.5 and 24.9 at your height. It opens in metric mode, with an imperial switch beside it, and there is a healthy-range view that shows the weight band for your height. Results round to one decimal place, so 22.857 shows as 22.9.
Height is the input people get wrong most often. Measure it without shoes, standing straight against a wall, and use your morning height if you want a consistent number. Weight is best taken on a flat, hard floor, in light clothing. If you are checking a child or teenager, use an age-and-sex percentile chart instead, because adult cut-offs do not apply to growing kids.
The maths, both ways
In metric units, it is one division:
BMI = weight (kg) ÷ height (m)²
If you measure in pounds and inches, the same idea needs a conversion factor:
BMI = 703 × weight (lb) ÷ height (in)²
At 70 kg and 1.75 m tall, square the height first: 1.75 × 1.75 = 3.0625. Then divide: 70 ÷ 3.0625 = 22.857, which rounds to 22.9.
The healthy-weight range for this height comes from the same formula, run backwards. Multiply 3.0625 by 18.5 to get 56.7 kg, and by 24.9 to get 76.3 kg. So the range is roughly 56.7 to 76.3 kg.
In imperial units, the maths looks like this. Someone weighing 150 lb at 65 in tall: 703 × 150 = 105,450. Then 65² = 4,225. Finally 105,450 ÷ 4,225 = 24.96, which rounds to 25.0.
What the bands actually tell you
Most charts group adult BMI into four broad bands:
| BMI | How it is generally described |
|---|---|
| Below 18.5 | Below the healthy range |
| 18.5 – 24.9 | Healthy range |
| 25.0 – 29.9 | Above the healthy range |
| 30.0 and above | Well above the healthy range |
Those bands are a starting point for a conversation, not a diagnosis. BMI cannot tell muscle from fat, so a very muscular person can land above 25 while carrying little body fat. It also says nothing about where fat sits on the body, and belly fat carries more risk than fat on the hips and thighs. Pregnancy, older age, and some medical conditions all change how the number should be read. If your result sits outside the healthy range and you are unsure what to do with it, a clinician can look at the full picture: waist size, blood pressure, blood work, habits, and family history.
That is also where body fat percentage comes in. Two people can share a BMI of 24 and look quite different, because one carries more muscle and the other more fat. If you want that second angle, our body fat percentage calculator estimates it from a few tape measurements.
Still curious? The ideal weight calculator shows a healthy weight range by height, the calorie calculator estimates daily calories for maintenance, loss, or gain, and the BMR calculator works out what your body uses at rest. Two longer reads sit alongside these: How to calculate BMI, a step-by-step guide to the formula, and What is a good BMI?, on healthy ranges, limits, and BMI versus body fat. You can also browse all health calculators and all calculators on CalcKits.
Frequently asked questions
What counts as a good BMI?
For most adults, the range 18.5 to 24.9 is generally described as healthy. There is no single ideal number inside it, and the same BMI can mean different things depending on muscle, age, pregnancy, and health history.
Can I work out BMI by hand?
Yes. Divide your weight in kilograms by your height in metres squared. For example, 70 kg at 1.75 m gives 70 ÷ 3.0625 = 22.9. In pounds and inches, use 703 × weight (lb) ÷ height (in) squared.
How much should I trust the number?
It is a useful screening tool, but a rough one. It does not measure body fat, muscle, or fat distribution, and it fits some bodies better than others. Treat it as one data point alongside waist size, activity, and how you actually feel.
Does the formula change for men and women?
No, the formula is the same for men and women. What differs is the context: muscle mass, body fat distribution, and life stages such as pregnancy change how a result should be read, which is why a conversation with a clinician beats a number on its own.
Nothing on this page is medical advice, a diagnosis, or treatment, and it cannot stand in for a qualified health professional who knows your history. If something about your health worries you, or anything feels urgent, get urgent care rather than waiting on a calculator result.
Sources
- Centers for Disease Control and Prevention: About Adult BMI
- National Health Service (NHS): BMI healthy weight guidance
- World Health Organization: Physical status: the use and interpretation of anthropometry