Here is a number your doctor probably mentions at every checkup, your health insurance cares about, and most of us have never actually calculated ourselves: your BMI. Body Mass Index sounds like something that requires a lab, a nurse, and a clipboard. In reality, it is one simple division problem — and you can do it in about thirty seconds with nothing but your height and weight.
This guide walks you through exactly how to calculate your BMI by hand (both the metric and the imperial versions of the formula), shows you the official BMI chart so you can read your result, and explains what the number actually means — and where it falls short. And if you would rather skip the math entirely, our free BMI calculator does it instantly.
BMI stands for Body Mass Index. It is a single number that estimates whether your weight is in a healthy range for your height. The World Health Organization and the CDC still use the same categories today.
BMI is a screening tool, not a diagnosis. It does not measure your body fat directly. What it does brilliantly is give doctors, researchers, and you a fast, cheap, standardized starting point.
Say you weigh 150 lb and you are 5′6″ tall (66 inches).
BMI = 24.2 — in the normal range.
Say you weigh 70 kg and you are 1.75 m tall.
BMI = 22.9 — also in the normal range.
| BMI range | Category | What it generally signals |
|---|---|---|
| Below 18.5 | Underweight | Possibly not getting enough nutrition; worth discussing with a doctor |
| 18.5 – 24.9 | Normal (healthy) weight | Weight is in the range linked with the lowest health risks |
| 25.0 – 29.9 | Overweight | Elevated risk for several conditions; lifestyle changes often help |
| 30.0 and above | Obese | Higher risk category; a doctor can help build a plan |
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For adults aged 20 and up, the same ranges apply: 18.5–24.9 is considered normal. Children and teens use separate BMI-for-age percentile charts.
No — the formula and categories are identical for adult men and women.
Once a month is plenty. Weigh yourself at the same time of day and compare month to month.
Yes — metric: weight in kg divided by height in meters squared. Imperial: 703 times weight in pounds, divided by height in inches squared.
A BMI of 30.0 or higher is classified as obese: Class I (30–34.9), Class II (35–39.9), Class III (40+).
BMI only measures the weight-to-height ratio — it says nothing about fitness, diet, sleep, or bloodwork. See a doctor rather than trusting the number alone.
Enter your height and weight — get your BMI and category instantly. Free, no signup.
Open BMI Calculator →Related tools: Age Calculator · Percentage Calculator · EMI Calculator