What Is a Good BMI? How to Read and Use Your Number
Body Mass Index (BMI) is one of the most widely used health screening numbers in the world — your doctor probably has it on file. It's a quick estimate of whether your weight is in a healthy range for your height. But a number is only useful if you understand what it means and what it doesn't, so let's unpack both.
How BMI is calculated
BMI is your weight divided by your height squared:
BMI = weight (kg) ÷ height (m)2
For example, someone 1.75 m tall weighing 70 kg has a BMI of 70 ÷ (1.75 × 1.75) = 22.9. If you think in pounds and inches, there's an imperial version, but the metric one is the standard.
What the ranges mean
The World Health Organization defines these adult categories:
- Below 18.5 — underweight
- 18.5 to 24.9 — healthy weight
- 25 to 29.9 — overweight
- 30 and above — obese
So our example BMI of 22.9 sits comfortably in the healthy range. You can read the full official definitions on the WHO obesity fact sheet.
Where BMI falls short
This is the important part most people miss. BMI doesn't distinguish between muscle and fat, so a very muscular athlete can register as "overweight" while being extremely healthy. It also doesn't account for age, sex, ethnicity, or where you carry weight — and waist circumference is often a better indicator of health risk. Treat BMI as a starting screening number, not a diagnosis.
Use it as one signal among several
A healthy BMI alongside good blood pressure, activity levels, and waist measurement paints a fuller picture than any single number. If your BMI sits outside the healthy range, it's a prompt to talk to a doctor — not a verdict.
Check yours in seconds
Our free BMI calculator works it out instantly in metric or imperial units and tells you which range you fall into — no mental arithmetic required.
Bottom line
BMI is a fast, useful screening tool: weight over height squared, slotted into four ranges. Just remember its limits — it's a conversation starter with your health, not the final word. Combine it with other measures for a picture you can actually act on.
