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BMI Calculator

Work out your Body Mass Index in metric or imperial units and see which category it falls into — underweight, healthy, overweight or obese — along with the healthy weight range for your height. Quick context for your health, with honest explanations of what BMI can and can't tell you.

Units

Metric (kg / cm) Imperial (lb / ft + in)

Weight (kg)

Height (cm)

—Your BMI

—Category

—Healthy range for you

What BMI Is — and What It Isn't

BMI (Body Mass Index) is a simple formula with a long history: your weight in kilograms divided by the square of your height in meters. It was devised in the 1830s by the Belgian statistician Adolphe Quetelet and adopted worldwide because it needs nothing but a scale and a tape measure. Doctors and insurers use it as a first-pass screening tool: across large populations, BMI correlates reasonably well with body fat and with risk for conditions like type 2 diabetes and heart disease.

Here's the honest part, because it matters: BMI knows nothing about you specifically. It can't tell muscle from fat, so a strength athlete can land in "overweight" with low body fat. It doesn't show where fat is carried, it behaves differently across ethnicities and ages, and it was never designed to diagnose anything. Used properly, it's a conversation starter — one number to discuss with a doctor alongside waist size, blood pressure, activity and family history. Used carelessly, as a verdict on a person's health, it misleads. This calculator gives you the number and the context together.

How to Use the BMI Calculator

Choose your units: Metric (kilograms and centimeters) or Imperial (pounds, feet and inches).
Enter your weight and height. For the most consistent number, weigh yourself in the morning and measure height barefoot — most of us are a touch shorter by evening.
Click "Calculate BMI" to see your score, its category, and the healthy weight range calculated for your specific height.
Re-check over time rather than daily. Weight naturally fluctuates by a kilogram or two with water and meals; trends over months are what count.

A Worked Example

Meet a typical case: 70 kg, 175 cm tall. The math is 70 ÷ 1.75² = 70 ÷ 3.0625 = 22.9 — comfortably inside the healthy band of 18.5 to 24.9.

The calculator also flips the formula around: for 175 cm, the healthy weight range is 56.7 kg to 76.3 kg. Now the same person at 85 kg gets a BMI of 27.8 — "overweight" — and can see they'd need to lose about 8.7 kg to reach the top of the healthy range. At 52 kg, BMI drops to 17.0, "underweight", a reminder that the scale has a healthy floor as well as a ceiling, and that being underweight carries its own risks.

Making Sense of Your Number

Underweight (below 18.5): may signal under-nutrition or an underlying condition. Worth a chat with a doctor, especially if unintentional.
Healthy (18.5–24.9): the range associated with the lowest population-level risk. Staying active matters even here — a healthy BMI with zero exercise isn't the full picture.
Overweight (25–29.9): a nudge, not an alarm. Many people in this band are metabolically healthy, but risk begins climbing, and waist circumference adds useful context.
Obese (30 and above): risk of several chronic conditions rises more steeply. A doctor can help separate what the number means for you personally and what to do about it.

Common Mistakes to Avoid

Using BMI for children and teens. Under-20s need age- and sex-specific percentile charts, not the adult cutoffs. A BMI of 22 means something different at 12 than at 32.
Treating it as a body-fat percentage. It isn't one. Two people with identical BMIs can have very different body compositions — a rugby player and a sedentary office worker are the classic example.
Obsessing over decimal points. The difference between 24.9 and 25.1 is a glass of water and a rounding line, not a health cliff. Categories are guide rails, not cliffs.
Self-diagnosing from one number. BMI is a screening tool. Pregnant women, the elderly, and very muscular people in particular should interpret it only with professional guidance.

Frequently Asked Questions

How is BMI calculated?

BMI = weight (kg) ÷ height (m)². In imperial units the equivalent is 703 × weight (lb) ÷ height (in)². This calculator handles the conversions for you, which is why metric and imperial entries for the same person give the same result.

What is a healthy BMI range?

For adults, the standard categories are: underweight below 18.5, healthy 18.5–24.9, overweight 25–29.9, and obese 30 or above. These are the WHO cutoffs used by most doctors and health organizations.

My BMI says overweight but I'm muscular. Is it wrong?

Quite possibly, for you. BMI can't distinguish muscle from fat, and muscle is denser. Athletes and manual workers often score “overweight” with genuinely low body fat. Waist circumference, body-fat measurements and a doctor's assessment fill in what BMI leaves out.

Does BMI apply to children?

Not with these cutoffs. Children and teens are assessed with BMI-for-age percentiles that account for growth and sex. Use a pediatric chart or ask your child's doctor instead.

How often should I check my BMI?

Monthly is plenty for tracking a trend. Daily weighing mostly measures water. What matters is the direction over months, combined with how you feel, your energy, and other health markers.

Can I lower my BMI safely?

Gradual is the watchword — most guidance aims for steady changes in eating and activity rather than crash diets, which typically rebound. If your BMI is in the obese range or you have other conditions, involve a doctor or dietitian from the start rather than going it alone.